Recent Advances in Dual Palladium Photoredox Catalysis

Shivam Vispute; Arpan Patel; Mohan Mokariya; Shreeya Dave; Yash Dhaduk; Maulik Pethani; Prabhakara Madivalappa Davanagere; Kishor Padala; Togati Naveen

doi:10.1002/asia.70968

. 2026 Aug 25;21(16):e70968. doi: 10.1002/asia.70968

Recent Advances in Dual Palladium Photoredox Catalysis

Shivam Vispute ^1,^#, Arpan Patel ^1,^#, Mohan Mokariya ¹, Shreeya Dave ¹, Yash Dhaduk ¹, Maulik Pethani ¹, Prabhakara Madivalappa Davanagere ², Kishor Padala ^2,^✉, Togati Naveen ^1,^✉

PMCID: PMC13504657 PMID: 42639715

ABSTRACT

Dual palladium/photoredox catalysis has emerged as a versatile platform for constructing complex molecular architectures. These systems enable a broad range of transformations by integrating palladium's well‐established roles in C─H activation and cross‐coupling with the single‐electron transfer capabilities of photocatalysts. Recent developments (2022–2026) in dual Pd/photoredox catalysis, from a mechanistic standpoint, reveal two interconnected activation pathways: conventional Pd(0)/Pd(II) catalytic cycles and photoredox‐driven radical generation. This review focuses on mechanistic insights governing atom‐ and radical‐transfer processes, encompassing diverse transformations such as C─C and C─X bond formation as well as late‐stage functionalization. Furthermore, it provides a conceptual framework that distinguishes dual Pd/photoredox catalysis from traditional palladium‐only or photocatalytic approaches by analyzing the interplay between these two catalytic regimes.

Keywords: dual palladium photoredox catalysis, metallaphotoredox catalysis, single‐electron transfer

In this review, we present a detailed and structured analysis of recent advances (2022–2026) in dual palladium photoredox catalysis, with a particular focus on classification according to product formation.

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1. Introduction

Over the past few decades, the use of transition‐metal catalysis has been unmatched due to its significant impact on synthetic chemistry. Transition metals' unique ability to exist in multiple oxidation states and coordination geometries makes them effective in catalyzing various bond‐forming and bond‐breaking reactions with excellent selectivity. This revolutionary trait has made them highly valuable in synthetic methods and, more broadly, in creating organic materials beneficial to society. The common approach in all these catalytic reactions is to rapidly assemble complex and valuable molecular structures from easily accessible starting materials. However, all this progress is still based on three fundamental principles of catalyst design: ligand design, controlling metal oxidation states, and electronic excitation. These core principles remain highly effective and continue to drive innovation in catalytic science [1, 2, 3, 4, 5, 6, 7]. Therefore, developing catalytic procedures that deliver high efficiency and selectivity has become a major focus in organic synthesis. The continuous need to improve reaction performance, expand substrate scope, and enhance functional group tolerance has encouraged the re‐evaluation of traditional synthetic strategies, thereby driving methodological advancements and addressing evolving demands in both academic and industrial needs [8, 9].

Among all transition metals, palladium has become one of the most powerful and versatile catalysts, enabling a wide range of transformations from traditional cross‐coupling reactions to more complex C─H functionalization and reduction processes; thus, reducing side reactions and increasing yields [10, 11, 12]. The significance of palladium‐catalyzed reactions is underscored by their recognition in the 2010 Nobel Prize in chemistry, which honored advancements in palladium‐catalyzed cross‐coupling reactions [13]. The broad acceptance of palladium catalysis is largely due to its intriguing organometallic chemistry and its ability to reversibly change its oxidation state, most often between Pd(0) and Pd(II), but sometimes involving higher oxidation states such as Pd(III) and Pd(IV) [14, 15, 16]. This allows palladium to participate very effectively in key catalytic steps such as oxidative addition, migratory insertion, trans‐metalation, and reductive elimination, which collectively form the mechanistic foundation for many bond‐forming reactions [17, 18, 19]. As a result, palladium catalysis has become a vital element in the synthesis of advanced materials, fine chemicals, agrochemicals, and pharmaceuticals [20]. Despite these advantages, there are some inherent drawbacks in traditional palladium‐catalyzed reactions. These often require strong bases or oxidizing agents, high temperatures, and very specific reaction conditions. Additionally, conventional palladium catalysis generally depends on prefunctionalized substrates and is often based on closed‐shell two‐electron processes, which are not suitable for generating radical intermediates that could otherwise facilitate unconventional bond disconnection and new selectivity patterns [21, 22, 23].

In this regard, visible light photoredox catalysis is highly beneficial, as it has minimal environmental and economic impacts associated with organic synthesis [24, 25, 26, 27]. The photoredox catalysts use light as an energy source to drive chemical reactions through various mechanisms such as photoredox catalysis, organometallic excitation, light‐induced atom transfer, and energy transfer [29, 30]. In such reactions, light absorption triggers electron transfer that produces reactive intermediates, which are the primary cause of chemical reactivity. The course of a photochemical reaction is mostly dependent on the photophysical properties of the excited molecule [31, 32, 33, 34]. Interestingly, organometallic complexes have longer microsecond lifetimes than organic dyes, which can be attributed to their more intricate electronic structures, spin multiplicities, and allowed and prohibited transitions [35, 36, 37, 38]. Iridium and ruthenium complexes have been widely employed as transition metal‐based photocatalysts [39]. The low energy of the ligand π* orbitals, which enables effective metal‐to‐ligand charge transfer upon light absorption, is the reason for their extensive utilization [40]. Although metal‐free organic photocatalysts are generally less expensive and their use has been increasing [41, 42, 43, 44], a substantial number of reported systems still rely on Ru‐ and Ir‐based photocatalysts, indicating that the field continues to depend significantly on precious‐metal‐based systems. By utilizing visible light as a renewable energy source, both types of photocatalysts (PCs) can effectively produce reactive radical species (PC*), encouraging single‐electron transfer (SET) processes. In reductive quenching, PC* accepts an electron from a substrate or reductant to form a radical anion, which is subsequently oxidized. In contrast, oxidative quenching is commonly involved in C─H functionalization, where PC* donates an electron to a substrate or oxidant, generating a radical cation that is later reduced (Figure 1) [45, 46].

Photoredox catalysis via reductive and oxidative pathways.

Furthermore, the ability of photoredox catalysis to precisely control reaction conditions enhances functionalization selectivity in aromatic systems. These catalysts enable the activation of readily available radical precursors, such as aryl diazonium salts, redox‐active esters, alkyl halides, and sulfones. Additionally, access to open‐shell intermediates has opened new reaction pathways that are difficult or impossible to achieve with conventional thermal methods. However, it often lacks precise control over bond‐forming selectivity and struggles with two‐electron processes like cross‐coupling [45, 46, 47].

Palladium complexes exhibit notable photophysical similarities to classical ruthenium bipyridine complexes, as suitably ligated Pd species can absorb visible light and access excited states through metal‐to‐ligand charge transfer transitions with significant redox activity. This intrinsic photoactivity has enabled the development of photoinduced palladium catalysis, in which palladium itself serves as both the light‐absorbing species and the catalytic center [47, 48, 49]. A seminal contribution by Gevorgyan and co‐workers demonstrated that visible‐light excitation of Pd(0) enables direct single‐electron transfer (SET) to aryl iodides, generating hybrid aryl Pd–radical intermediates without the need for an external photosensitizer (Figure 2). These species display dual organometallic and radical character, enabling unconventional reactivity such as 1,5‐hydrogen atom transfer (HAT) followed by β‐hydride elimination, thereby facilitating transformations. In contrast to traditional two‐electron Pd catalysis, these processes proceed via excited‐state SET pathways, often involving oxidative quenching with electrophiles through inner‐sphere electron transfer steps characterized by low activation barriers, thus expanding the mechanistic landscape of palladium catalysis [50, 51].

Despite these advances, the reliance on the intrinsic photophysical properties of Pd complexes imposes limitations, including relatively short excited‐state lifetimes and restricted redox flexibility. To address these challenges, dual palladium photoredox catalysis has emerged as a synergistic approach combining two distinct catalytic modes [49, 52]. It has its origins in the advent of visible‐light photoredox catalysis, pioneered by MacMillan, Yoon and Stephenson in the late 2000s, which enabled the mild generation of radical intermediates via single‐electron transfer (SET) processes [53, 54, 55]. The conceptual breakthrough enabling this field came in 2014, when MacMillan, Molander, and Doyle independently demonstrated the merger of photoredox catalysis with transition‐metal catalysis, establishing the paradigm of metallaphotoredox catalysis. These studies revealed that photogenerated radicals could be efficiently intercepted by metal catalytic cycles, unlocking previously inaccessible bond constructions [56, 57, 58, 59]. Shortly thereafter, Glorius formalized the concept of dual catalysis, emphasising the synergistic interplay between photoredox and transition‐metal pathways [60, 61, 62, 63]. Building on this framework, palladium catalysis was incorporated into photoredox manifolds with key contributions from Yu and other groups, who demonstrated that Pd catalysis could operate via unconventional single‐electron pathways, enabling access to Pd(I), Pd(III), and Pd(IV) intermediates and thereby transcending classical Pd(0)/Pd(II) two‐electron cycles [45, 47, 49, 64, 67]. From 2018 onwards, dual Pd/photoredox catalysis rapidly evolved into a versatile synthetic platform and expanded the methodology to include decarboxylative cross‐couplings, C─H functionalisation and radical‐mediated bond constructions [65, 66, 67, 68].

In these systems, palladium facilitates bond formation via organometallic intermediates, while photocatalysts promote reactions through radical generation or single‐electron redox processes (Figure 3) [69, 70, 71, 72, 73]. By leveraging the synergistic effects of these two catalytic pathways, new mechanisms that are unachievable in traditional two‐electron redox reactions become possible, including access to high oxidation states of palladium such as Pd(I), Pd(III), and Pd(IV). Such system operates within its optimal redox regime, overcoming limitations associated with the relatively short‐lived excited states and weaker absorption profiles of Pd complexes. This method significantly broadens the range of palladium‐catalyzed reactions, enabling efficient C─C and C–heteroatom bond formation, radical cross‐coupling, selective C─H functionalization, and more [74]. Importantly, these reactions exhibit excellent functional group tolerance and are highly suitable for late‐stage modification of complex molecular structures, making them especially valuable in medicinal chemistry and complex molecule synthesis [75, 76, 77]. Some of the transition metal complexes and organic photocatalysts highlighted in this article are shown in Figure 4.

List of photoredox catalysts used in this review.

To provide a comprehensive overview of the rapid progress in this field, the developments reported in dual palladium/photoredox catalysis have been organized by the type of bond formation and functionalization achieved. This review categorizes the reactions into seven groups: acylation, arylation, allylation, alkylation, esterification, cross‐coupling, and miscellaneous reactions.

The transformations discussed is this review underscore that the principal advantage of dual palladium photoredox catalysis lies not only in enabling C─H activation itself; since palladium‐mediated activation pathways is already well established, but in expanding the range of coupling partners through photochemically generated radical intermediates. While photoredox catalysis alone efficiently generates such radicals, but it lacks the site‐selectivity and bond‐forming control imparted by palladium, highlighting the complementary nature of the dual system. More broadly, dual catalysis strategies have also been developed using other transition metals such as Ni, Cu, Fe, and Co; however, these systems typically favour radical capture pathways and operate through distinct mechanistic regimes that can differ in selectivity, scope, and functional group tolerance. In contrast, dual Pd/photoredox catalysis benefits from the well‐established versatility, predictability, and functional group compatibility of palladium catalysis, while simultaneously expanding its reactivity through photoredox activation. Consequently, this approach represents a uniquely powerful platform that bridges classical cross‐coupling chemistry with modern radical‐based transformations.

2. Strategies for Acylation Reactions

In this section, the photocatalyst converts precursors such as α‐oxocarboxylic acids into acyl radicals via oxidative decarboxylation, which subsequently engage palladacycles to access Pd(III)/Pd(IV) intermediates through single‐electron pathways, thereby overcoming the limitations of conventional two‐electron palladium catalysis which requires acyl partners (e.g., acyl halides, anhydrides) suffering from less controlled radical generation and competing side reactions. Accordingly, this section is classified into C(sp²)‐H acylation involving directing‐group‐assisted cyclopalladation via CMD pathways, subdivided based on acyl sources such as phenylglyoxylic acids and aldehydes, as well as C(sp³)‐H acylation proceeding through 1,n‐HAT pathways.

Importantly, different acyl sources exhibit distinct mechanistic and practical implications that define the scope of these transformations. α‐Oxocarboxylic acids (e.g., phenylglyoxylic acids) are most commonly employed due to their efficient and clean radical generation under comparative mild oxidative conditions, typically enabling good functional group tolerance and operational simplicity. In contrast, aldehydes, although more readily available, generally require strong oxidants such as TBHP or TBPB to generate acyl radicals via hydrogen atom abstraction (HAT), which can compromise selectivity, safety, and sustainability. Alternative precursors such as hydroxamides and oxime esters generate acyl radicals via N–O bond cleavage, often under milder or redox‐neutral conditions, but at the expense of additional pre‐functionalization steps, reducing step economy. Similarly, fragmentation‐based approaches can furnish acyl radicals but often suffer from less controlled radical generation and competing side reactions. Mechanistically, these variations influence not only the efficiency of radical formation but also their subsequent capture by palladacycles and progression through Pd(III)/Pd(IV) manifolds.

2.1. C(sp²)‐H Acylation Involving Directing‐Group‐Assisted Cyclopalladation Through CMD‐Type Pathways

2.1.1. Using Phenyl Glyoxylic Acids as Acyl Source

In 2022, Kshirsagar and his team reported an approach for the decarboxylative ortho C─H aroylation of 2‐aryl‐pyrido[1,2‐a]pyrimidin‐4‐ones and thiazolopyrimidinones.(Scheme 1) They initiated their study using 2‐phenyl‐4H‐pyrido[1,2‐a]pyrimidin‐4‐one 1 and phenylglyoxylic acid 2 as model substrates to optimize the reaction conditions. The optimized conditions were found to be 15 mol% Pd(OAc)₂, 4 mol% [Ru(bpy)₃]Cl₂·6H₂O, 4 equiv. of O₂, and 0.2 mL TFA in 4.0 mL AcOH as the solvent, under 458 nm blue LED irradiation at room temperature for 28‐48 h [78].

SCHEME 1 — Substrate scope of decarboxylative aroylation.

After optimizing the reaction conditions, the authors examined the substrate scope of the reaction. They first studied the scope of pyrido[1,2‐a]pyrimidin‐4‐ones and found that when methyl groups were present at various positions on the pyrido‐pyrimidin‐4‐one ring, the reaction produced good to excellent yields. Halogen‐substituted substrates also yielded good results. When electron‐donating groups such as methyl or methoxy were attached to the 2‐phenyl ring, the reaction resulted in moderate yields. Additionally, they explored the scope of different substituted phenylglyoxylic acids and discovered that acids with moderate electron‐withdrawing groups, such as F, Cl, or Br, gave good yields. Notably, a strong electron‐withdrawing group like nitro on phenylglyoxylic acid led to low yields. However, when 2‐oxopropanoic acid was reacted with 2‐phenyl‐4H‐pyrido[1,2‐a]pyrimidin‐4‐one, no desired product was observed.

To understand the possible reaction pathway, the authors performed several mechanistic studies and, based on these investigations, they proposed a plausible mechanism (Scheme 2). Initially, upon visible‐light irradiation, tris(bipyridine)ruthenium(II) chloride ([Ru(bpy)₃]² ⁺) undergoes photoexcitation to generate the excited state [Ru(bpy)₃]² ⁺*. This excited photocatalyst oxidizes phenylglyoxylic acid 2 to produce intermediate 4 while being reduced to [Ru(bpy)₃]⁺. Subsequently, intermediate 4 undergoes decarboxylation to generate the acyl radical intermediate 5. The reduced photocatalyst [Ru(bpy)₃]⁺ is then oxidized back to [Ru(bpy)₃]² ⁺, thereby completing the photoredox catalytic cycle. Meanwhile, the palladium catalytic cycle is initiated through C─H activation of 2‐phenyl‐pyrido[1,2‐a]pyrimidin‐4‐one, leading to the formation of a palladacycle intermediate 6. This intermediate then undergoes oxidative radical coupling with the acyl radical 5, affording a putative Pd(III) intermediate 7, which is further oxidized under oxidative conditions to form the Pd(IV) intermediate 8. Finally, reductive elimination from intermediate 8 yields the desired acylated product 3, along with regeneration of the Pd(II) species, which re‐enters the catalytic cycle.

In 2022, Nidhi Jain and co‐workers reported ortho‐benzoylated N‐aryl‐7‐azaindole synthesis using palladium/photoredox dual‐catalysis facilitated by visible light (Scheme 3). Phenylglyoxylic acid 2 and N‐phenyl‐7‐azaindole 9 were used as model substrates with optimized conditions identified as 10 mol% of Pd(OAc)₂, 3 mol% of Eosin Y, and 1 equiv. of AgNO₃ in 3 mL of MeCN under an oxygen atmosphere, utilizing 10 W blue LED irradiation for 40 h at room temperature [79].

SCHEME 3 — Decarboxylative *ortho*‐benzoylation of N‐phenyl‐7‐azaindoles.

The substrate scope of N‐aryl‐7‐azaindoles was thoroughly examined. Both electron‐donating and electron‐withdrawing groups on the N‐phenyl ring were compatible, producing ortho‐benzoylated products in moderate to excellent yields, with electron‐withdrawing groups generally providing higher yields. Meta‐substituted substrates also performed well, while ortho‐substituted N‐phenyl derivatives were unreactive due to steric hindrance. Modifications on the 7‐azaindole core showed that substituents at the C‐3, C‐4, and C‐5 positions, including halogens, acetyl, aryl, and heteroaryl groups were well tolerated and yielded corresponding products in good to excellent yields. The decarboxylative coupling scope was also expanded to various α‐oxo acids, where electron‐withdrawing groups on phenyl glyoxylic acids resulted in higher yields compared to electron‐donating groups.

As outlined in Scheme 4, a plausible pathway involved visible‐light excitation of Eosin Y to EY*, which initiates single‐electron transfer to the α‐oxo acid, producing a benzoyl radical 5 through oxidative decarboxylation and reduced EY^•− species. The reduced EY^•− species transfers an electron to molecular oxygen, regenerating Eosin Y and forming the superoxide radical anion (O₂ ^•−). Palladium‐mediated ortho C─H activation of N‐aryl‐7‐azaindole simultaneously produces a palladacycle intermediate 11, which oxidizes to Pd(IV) intermediate 13 by forming O₂ ² ⁻ and H₂O₂ after reacting with benzoyl radical 5 to form Pd(III) intermediate 12. Finally, the ortho‐benzoylated product 10 is obtained through reductive elimination from 13 and regenerates the Pd(II) catalyst.

The dual palladium‐photoredox‐mediated regioselective acylation of carbazoles 14a and indolines 16 was reported by Purushothaman Gopinath and coworkers in 2023. Phenylglyoxylic acid 2 and 9‐(pyrimidin‐2‐yl)‐9H‐carbazole served as model substrates in the initial part of their study to optimize reaction conditions. They found that using 1 mol% of Ru(bpy)₃Cl₂ and 10 mol% of Pd(OAc)₂ in MeCN (0.2 M) at room temperature with Kessil blue LED irradiation and O₂ for 24‐48 h yielded the best results (Scheme 5). The scope of the reaction was then extended to indoline derivatives 16, which required modified conditions ‐ 5 mol% of Eosin Y and 10 mol% of Pd(OAc)₂ in trifluorotoluene (0.2 M) at room temperature under Kessil blue LED irradiation and O₂ for 24‐48 h [80].

SCHEME 5 — Regioselective acylation of carbazoles and indolines.

After obtaining optimal conditions, the authors explored the substrate scope of various phenylglyoxylic acids, carbazoles, and indoline derivatives. They found that phenylglyoxylic acids with halogen and electron‐rich substituents at the para‐position gave good yields. Similarly, disubstituted phenylglyoxylic acids also resulted in good yields. However, heteroaromatic glyoxylic acids produced moderate yields, and aliphatic α‐keto acids gave lower yields. They then used more phenylglyoxylic acid and chlorobenzene as the solvent to investigate the possibility of diarylation of carbazoles. They discovered that 4‐methylglyoxylic acid and simple phenylglyoxylic acid yielded the diacylated compounds effectively. In this study, they observed that 2‐substituted carbazoles produced moderate to good yields of acylated compounds, with the acyl group attaching to the less hindered phenyl ring of the carbazole. The same compounds were also obtained in good yields from disubstituted carbazoles. Finally, they examined the range of indoline derivatives and found that different indoline compounds selectively produced C7‐acylated products in high yields.

To comprehend the reaction process, the authors undertook mechanistic investigations and, based on these results, postulated a probable mechanism (Scheme 6). First, carbazole 14a interacts with Pd(II) acetate to create intermediate 18. At the same time, an acyl radical 5 is created through the photocatalytic cycle, which subsequently reacts with intermediate 18 to form intermediate 19. In the photocatalytic cycle, two potential paths exist for the formation of the acyl radical 5. In Path A, the Ru(bpy)₃Cl₂ photocatalyst is excited by blue LED light to form the excited photocatalyst PC*, which undergoes oxidative quenching in the presence of O₂ to generate the superoxide ion and the oxidized photocatalyst PC^•+. After that, photocatalyst PC^•+ and phenylglyoxylic acid 2 conduct single‐electron transfer (SET) to create a new radical intermediate. This intermediate then proceeds through deprotonation and decarboxylation to produce the acyl radical 5 and recreate the ground‐state photocatalyst. Similar to this, in Path B, blue LED light excites the Eosin Y photocatalyst to create the excited‐state photocatalyst PC*. This species proceeds through SET with phenylglyoxylic acid 2 to create a radical intermediate, which is subsequently deprotonated and decarboxylated to provide the acyl radical 5. The reduced photocatalyst PC^•− subsequently undergoes SET with O₂ to form the corresponding ground‐state photocatalyst. The acyl radical 5 generated from both Path A and Path B oxidizes intermediate 18 to the corresponding intermediate 19 and subsequently forms intermediate 20 by reacting with superoxide ion to form hydroperoxide ion. Finally, intermediate 20 undergoes reductive elimination to form the final product 15 and regenerate the Pd(II) catalyst

In 2023, Nidhi Jain and co‐workers developed a visible‐light‐promoted photoredox/palladium‐catalyzed site‐selective acylation of N‐protected carbazoles 14b (Scheme 7). They began their study using 9‐(pyrimidin‐2‐yl)‐9H‐carbazole and phenylglyoxylic acid 2 as model substrate for acylation which involved 2 mol% of Eosin Y, 10 mol% of Pd(OAc)₂, 2 mL of xylene as solvent, under blue LED and oxygen atmosphere at room temperature for 36 h as optimized condition [81].

SCHEME 7 — C─H acylation of N‐protected carbazoles.

After optimizing the reaction conditions, the authors explored the substrate scope using various glyoxylic acids. Quinoline‐derived substrates bearing glyoxylic acids with both electron‐donating and electron‐withdrawing substituents afforded the corresponding products in moderate yields, with electron‐donating groups giving higher yields than electron‐withdrawing groups. Halogen‐substituted carbazoles furnished the desired products in moderate yields, whereas nitro‐substituted carbazoles failed to produce the corresponding products. The pyridyl group on di‐halo‐substituted carbazoles afforded the desired products in moderate yields, indicating no significant effect on reactivity. N‐pyridyl‐substituted di‐halogenated carbazole derivatives gave low yields, while 2,7‐dibromo‐9‐pyridinyl carbazole did not afford the desired product. Unsymmetrical 3‐methyl‐9‐pyridinyl carbazole produced a mixture of regioisomers in moderate yield.

To understand the possible reaction pathway, the authors proposed a plausible mechanism (Scheme 8). Eosin Y was excited under blue LED irradiation to generate the photoexcited species Eosin Y*. This Eosin Y* species upon SET oxidation process form an acyl radical 5 from aryl glyoxylic acid 2. Thereafter, substrate 14b with Pd(OAc)₂ undergoes directed aromatic C─H activation via a concerted metalation–deprotonation (CMD) pathway to form the palladium complex 22. This complex 22 reacts with acyl radical 5 to give a Pd intermediate 23 and subsequently forms another Pd intermediate 24 by reacting with superoxide ion. Finally, intermediate 24 undergoes reductive elimination to form the final product 21.

The regioselective decarboxylative acylation of N‐methyl‐3‐phenylquinoxalin‐2(1H)‐one by dual palladium‐photoredox catalysis was reported by Brajendra and his team in 2023 (Scheme 9). To improve the reaction conditions in the first phase of their study, they employed phenylglyoxylic acid 2 and 1‐methyl‐3‐phenylquinoxalin‐2(1H)‐one 25 as model substrates. The optimal standard conditions were found to be 7.5 mol% of Pd(OAc)₂, 30 mol% of fluorescein dye, and 8.0 equivalents of TBPB in ethanol exposed to blue LED for 25 h at room temperature [82].

SCHEME 9 — Regioselective decarboxylative acylation of N‐methyl‐3‐phenylquinoxalin‐2(1H)‐one.

The authors investigated the substrate scope of this reaction after optimizing the reaction conditions. They first explored a variety of keto acids and discovered that phenylglyoxylic acids with various substituents, like ‐OMe, ‐CH₃, ‐F, ‐Cl, and ‐Br, produced the corresponding products in moderate to good yields. Subsequently, they looked at variously substituted 1‐methyl‐3‐phenylquinoxalin‐2(1H)‐ones and found that superior yields were obtained when the 3‐phenyl ring (ring B) had an electron‐donating group at the para position as opposed to electron‐withdrawing groups like ‐F and ‐Cl at the same position. They also observed that replacing the methyl group on the keto acid with a methoxy group led to a decrease in yield. The compounds were similarly synthesized in good yields using heterocyclic analogues of 1‐methylquinoxalin‐2(1H)‐one.

Finally, the authors conducted mechanistic studies to determine the possible route of this reaction and proposed a plausible mechanism (Scheme 10). Initially, fluorescein dye (FI) undergoes photoexcitation to generate its excited state (FI*). Subsequently, it forms acyl radical 5 from phenylglyoxylic acid 2 in the SET process. Meanwhile, N‐methyl‐3‐phenylquinoxalin‐2(1H)‐one 25 coordinates with the Pd(II) catalyst to form intermediate 27. This intermediate 27 then reacts with acyl radical 5 to produce intermediate 28. Next, intermediate 28 undergoes single‐electron oxidation to generate intermediate 29, which helps to reduce the excited species of FI. The radical anion form of fluorescein then closes the photochemical cycle by generating a tert‐butoxide radical through back electron transfer. Intermediate 29 then undergoes reductive elimination to give the desired product 26.

In 2025, Pan Xie and co‐workers reported decarboxylative benzoylation of arylpyridines 30 with phenylglyoxylic acid 2 enabled by dual palladium photoredox catalysis. They began their study with phenylpyridine and benzoyl formic acid as a model substrate. The optimal conditions were determined to be 5 mol% of Eosin Y and 5 mol% of Pd(CH₃CN)₂Cl₂ with 1.5 equivalents of K₂S₂O₈ in 1 mL MeCN for 8 h under 5 W blue LED irradiation (405–410 nm) in the presence of air at room temperature (Scheme 11) [83].

SCHEME 11 — Decarboxylative benzoylation of aryl pyridines.

A broad range of benzoyl formic acids containing electron‐donating and electron‐withdrawing groups was efficiently converted in good yields, with negligible steric effects; notably, ortho‐substituted substrates performed comparably to para‐substituted substrates. Heteroaryl keto acids, such as furan‐ and thiophene‐derived substrates, were also compatible, affording products in moderate to good yields. Subsequently, the scope of aryl pyridines was explored. Ortho‐, meta‐, and para‐substituted phenyl pyridines with electron‐donating and electron‐withdrawing substituents afforded the desired benzoylated products in moderate to good yields. A slight steric effect was observed for ortho‐substituted substrates, while halogenated aryl pyridines were well tolerated, offering opportunities for further functionalization. The method further demonstrated excellent practicality, maintaining high efficiency on a gram scale with reduced catalyst loading.

A plausible mechanism suggested by this group is shown in Scheme 12. Eosin Y, upon visible‐light irradiation is excited to Eosin Y*, followed by oxidation via K₂S₂O₈ to generate Eosin Y^• ⁺. It reacts with benzoyl formic acid 2, causing CO₂ loss through a hydrogen‐atom transfer (HAT) process to form a benzoyl radical 5, while Eosin Y is regenerated to complete the cycle. Meanwhile, Pd(II) binds with phenyl pyridine 30 to form a cyclopalladated intermediate 32. The benzoyl radical 5 then adds through a single‐electron oxidative step to give a Pd(III) species 33, which is further oxidized by K₂S₂O₈ to form a Pd(IV) intermediate 34. Then, the Pd(IV) intermediate 34 upon reductive elimination forms the final product 31 and restores the Pd(II) catalyst (Path A). Alternatively, benzoyl radicals 5 may form via the HAT pathway from photoexcited Eosin Y*, followed by decarboxylation. These radicals similarly follow the Pd(II) → Pd(III) → Pd(IV) pathway to yield the final product 31 (Path B).

2.1.2. Using Aldehyde as Acyl Source

In 2023, Wenhai Huang and co‐workers successfully developed a protocol for acylation with aldehydes via dual C─H activation by combining photocatalysis and palladium catalysis. Initially, they used N‐benzyl‐1,1,1‐trifluoromethanesulfonamide 35 and 4‐(benzyloxy)benzaldehyde 36 as model substrates to optimize the reaction conditions. The best optimized conditions were found to be 0.03 mmol of Pd(OAc)₂, 0.45 mmol of TBHP, 0.015 mmol of plastoquinone (PQ), 0.075 mmol of acetic acid, and DMF: ACN = 1:1 (1 mL) (Scheme 13). After optimizing the reaction conditions, the substrate scope was investigated using various substituted aldehydes. They found that groups such as ‐CH₃, ‐OMe, ‐F, and ‐Cl present at the ortho, meta, and para positions provided moderate to good yields. Later, they investigated the acylation of several substituted N‐benzyl‐1,1,1‐trifluoromethanesulfonamides. Acylation with unsubstituted aldehydes, halogens, and ‐OMe, as well as other electron‐donating groups at different positions, produced the products in moderate to high yields [84].

SCHEME 13 — The acylation with aldehydes via dual C─H activations.

Finally, the authors proposed a plausible mechanism, which is shown in Scheme 14. First, PQ was excited by visible light and converted into PQ*. Thereafter aldehyde 36 undergoes hydrogen atom transfer to generate acyl radical 5 and PQ‐H. This species was further oxidized by TBHP to regenerate PQ. Meanwhile, the starting material 35 reacted with Pd(OAc)₂ to generate intermediate 38 through C─H activation, which trapped intermediate 5 to form intermediate 39. Intermediate 39 then underwent reductive elimination to generate the final product 37.

In 2024, Wanying Zhang and his team accomplished visible‐light‐induced palladium‐catalyzed C─H acylation of azobenzenes at room temperature. They started their study using azobenzene 40 and benzaldehyde 36 as model substrates and optimized the conditions as follows: 5 mol% of Pd(OAc)₂, 5 mol% of Eosin Y, 1.5 equiv of TBHP in 1.0 mL of DCE solvent under air at room temperature (25°C), and a blue LED (385–390 nm, 10 W) for 8 h (Scheme 15) [85].

SCHEME 15 — C─H acylation of azobenzenes.

Subsequently, the authors explored the substrate scope of various benzaldehydes containing both electron‐rich and electron‐poor substituents at different positions. They observed that substrates with substituents at the para‐position yielded the desired products in satisfactory yields. Additionally, benzaldehydes bearing electron‐rich groups delivered slightly higher yields compared to those containing electron‐withdrawing groups. Interestingly, p‐nitrobenzaldehyde showed good reactivity and produced the desired product in a significant yield. Next, they examined heterocyclic aldehydes, which afforded moderate yields. The acylation of benzaldehyde with various substituted azobenzenes provided the desired acylated products in moderate to good yields. For example, para‐methyl‐substituted azobenzene gave the desired product in a good yield; in contrast, the product was generated in a lesser yield by the sterically hindered ortho‐methyl‐substituted azobenzene.

Finally, the authors carried out mechanistic studies and proposed a plausible reaction mechanism based on their findings (Scheme 16). Initially, photoexcitation of Eosin Y generates the excited‐state species Eosin Y*. This species undergoes oxidation by TBHP to form a tert‐butoxy radical, a hydroxyl anion, and the Eosin Y^• ⁺. Upon completion of the photocatalytic cycle, the active species Eosin Y^• ⁺ reacts with benzaldehyde 36 to generate a benzoyl radical 5 while regenerating Eosin Y. Meanwhile, intermediate 41 is formed through C─H activation of azobenzene 40 via the palladium catalytic cycle. The benzoyl radical 5 then undergoes oxidative addition with intermediate 42 through a single‐electron transfer process, leading to the formation of a Pd(III) species and intermediate 43. Subsequent reductive elimination produces the desired product 41 and generates the Pd(I) intermediate 44. Finally, this intermediate 44 is reoxidized by the tert‐butoxy radical in the presence of AcOH, regenerating the Pd(II) catalyst and completing the catalytic cycle, with tert‐butanol 45 formed as a by‐product.

2.2. C(sp³)‐H acylation involving 1,n‐HAT pathways

In 2025, Ji Lu and co‐workers reported the first dual photoexcited palladium/photoredox strategy for remote C(sp³)‐H acylation of hydroxamides without using external acylating agents (Scheme 17). The method proceeds with high efficiency and good atom economy through a sequence involving N─O bond reduction, C─H activation, and C─O bond cleavage. It also shows broad substrate scope, making it suitable for late‐stage functionalization of complex molecules. They started optimization with O‐acylhydroxamide 46 as the model substrate. The optimal conditions employed were 2 mol% of [Ir{dF(Me)ppy}₂(dtbbpy)]PF₆, 10 mol% of Pd(PPh₃)₄, 12 mol% of DPEphos, 2 equiv. of PPh₃, and 1.5 equiv. of K₂HPO₄ in 0.1 M MeCN. The reaction was carried out under 30 W blue LED irradiation at room temperature for 24 h under an argon atmosphere [86].

SCHEME 17 — Remote C(sp³)‐H acylation of hydroxamides.

Under these conditions, O‐(p‐CF₃‐benzoyl)hydroxamides with various para‐substituents were obtained in moderate to excellent yields. Meta‐substituted substrates also produced good yields, while ortho‐methyl and chloro substituents resulted in moderate yields. Disubstituted aryl and naphthyl substrates performed well, whereas functionalized alkyl amides provided moderate yields. Replacing the O‐acyl group with the p‐CF₃‐benzoyl moiety and adding phenyl or para‐aryl substituents resulted in yields ranging from low to excellent. Ortho‐ or meta‐electron‐withdrawing groups yielded low to good results, and disubstituted benzenes gave moderate to good yields. The 2,4,5‐trifluorophenyl and pentafluorophenyl derivatives showed moderate yields. Naphthyl‐ and pyridyl‐based hydroxamides delivered good yields, while indolyl‐ and thienyl‐substituted substrates gave lower yields

Based on mechanistic investigation (Scheme 18), the authors propose that visible light excitation of the Pd(0)L_n forms an excited Pd(0) complex 48, which generates an amidyl radical 49 upon SET process along with a Pd(I) species and a benzoate anion. The amidyl radical 49 undergoes 1,5‐hydrogen atom transfer (1,5‐HAT) to form the corresponding radical 50, which combines with the Pd(I) species to give a Pd(II) intermediate 51. This intermediate 51 undergoes β‐hydride elimination to form a desaturated by‐product 52. Meanwhile, a PPh₃ radical cation, formed through the SET process between PPh₃ and the excited Ir(III) photocatalyst, promotes phosphoranyl radical‐mediated deoxygenation to form intermediate 53. Reductive elimination of 53 then furnishes the final product 47 and Pd(I) species, while Ir(II) reduces Pd(I) to regenerate Pd(0), completing the dual catalytic cycle.

Ji Lu and co‐workers developed a protocol for the editing of cycloketones via deoxygenative coupling in 2025 (Scheme 19). In their initial investigation, they used a cyclobutanone‐derived oxime ester 55 as a model substrate to optimize the reaction conditions. The optimal conditions were identified as 1 mol% of [Ir{dF(Me)ppy}₂(dtbbpy)]PF₆, 3 mol% of Pd(PPh₃)₄, 12 mol% of PCy₃, and 2.0 equivalents of PPh₃ in 0.1 M MeCN solvent, under irradiation with 30 W blue LEDs and an argon atmosphere at room temperature for 24 h [87].

Once the optimal conditions were identified, the authors next investigated the substrate scope. They first examined cycloketone derivatives and found that various arenes containing electron‐neutral, electron‐rich, or electron‐deficient groups at the para‐position, as well as at the α‐position of cyclobutanone derivatives, provided the corresponding products in moderate to excellent yields. Meanwhile, groups such as OMe or CO₂Me at the meta‐position afforded products in moderate yields. Similarly, disubstituted and 2‐naphthyl derivatives also gave the corresponding products in moderate yields. Bicyclic oxime esters with a cis‐configuration provided products in moderate yield and generated a new stereocenter. They also observed that less‐strained cyclohexanone oxime esters gave the corresponding products in low yields. Next, they focused on the acyloxy part and found that benzoyl rings with electron‐neutral, electron‐donating, halogen, or electron‐withdrawing groups at the ortho‐, meta‐, or para‐positions afforded the corresponding products in moderate yields. Interestingly, when a methoxy group was present at the para‐position, only a trace amount of product was obtained. Heteroaromatic formyl substrates also provided the desired products in moderate yields. Finally, they explored several pharmaceutical derivatives, obtaining the corresponding products in moderate to good yields.

Based on the results of mechanistic investigations and previously reported studies, the authors proposed a plausible reaction mechanism involving two possible pathways (Scheme 20). In the first pathway, the cycloketone oxime ester 55 is initially activated via a visible‐light‐induced single‐electron transfer (SET) process with the photoexcited Pd(0) complex. This interaction generates a hybrid Pd(I) iminyl radical species 57, accompanied by a benzoate counterion. The resulting radical intermediate 57 undergoes ring opening to form a cyanoalkyl radical–Pd(I) intermediate 58, which exists in equilibrium with a cyanoalkyl‐Pd(II) complex 59 formed through radical recombination. The equilibrium can shift toward the Pd(II) intermediate 59, which may undergo reductive elimination to produce a side product 60. Meanwhile, a phosphoranyl radical is generated via SET between triphenylphosphine and the excited Ir(III) photocatalyst. This phosphoranyl radical facilitates a deoxygenation step that converts the intermediate into a key organometallic species 61. Subsequent reductive elimination from this intermediate affords the desired product 56 along with a Pd(I) species 62. Finally, the Pd(I) species 62 is reduced by the Ir(II) complex, regenerating the Pd(0) catalyst and completing the catalytic cycle. In the second possible pathway, the excited Ir(III) photocatalyst interacts with triphenylphosphine via SET, producing both a phosphoranyl radical and an Ir(II) species. The Ir(II) species then reduces the cycloketone oxime ester 55 to generate a cyanoalkyl radical 63 along with a benzoate anion. Next, the benzoate anion undergoes phosphoranyl radical‐mediated deoxygenation to form an acyl radical intermediate 5. Finally, radical–radical coupling between the acyl radical 5 and the cyanoalkyl radical yields the final product 56.

Several commonly used acylating partners in traditional radical and palladium catalysis such as acyl halides, acid chlorides, symmetric anhydrides, and thioesters remain largely unexplored or incompatible in dual catalytic acyl radical systems, likely due to challenges associated with controlled radical generation, catalyst deactivation, or competing side reactions; expanding the scope to incorporate these readily available and industrially relevant acyl sources represents an important direction for improving the generality, practicality, and sustainability of these methodologies.

3. Strategies for Arylation Reactions

The transformations discussed in this section highlight generation and selective incorporation of aryl radicals as coupling partners. In contrast to conventional Pd catalysis, which relies on prefunctionalized aryl halides and two‐electron Pd(0)/Pd(II) cycles, the dual approach bypasses oxidative addition by engaging photochemically generated aryl radicals with Pd(II) palladacycles to access Pd(III)/Pd(IV) intermediates and enable reductive elimination. The choice of aryl precursor plays a crucial role in defining reactivity and practicality. Aryl diazonium salts, which dominate this section, readily form aryl radicals under mild conditions but suffer from stability and competing side reactions. In contrast, aryldibenzothiophenium salts, represented by a single example, offer improved stability but require pre‐functionalization. These differences influence radical generation efficiency and their subsequent engagement with palladacycles, highlighting how dual catalysis expands the scope beyond both palladium‐only and photoredox‐only strategies.

A palladium metallaphotoredox‐catalyzed approach for the selective C‐2 arylation of indole derivatives under visible light irradiation was developed by Wang and his co‐workers in 2022 (Scheme 21). Using N‐pyrimidyl indole 64 and aryldibenzothiophenium (Ar‐DBT⁺) salts 65 as model substrates, the optimized conditions employed 20 mol% of Pd(TFA)₂, 2 mol% of fac‐Ir(ppy)₃, 0.4 equivalents of phosphoric acid dibenzyl ester as ligand, 1 equivalent of Na₂CO₃, and 0.1 M MeCN using blue LED irradiation for 24 h at room temperature [88].

SCHEME 21 — Palladium metallaphotoredox‐catalyzed 2‑arylation of indole.

The substrate scope was explored using various indoles containing electron‐withdrawing and electron‐donating groups at the C4‐C6 positions, which showed good to excellent reactivity, affording the desired products in moderate to excellent yields. Halogenated indoles performed particularly well, enabling further downstream functionalization. Simple 3‐ and 7‐methyl indoles gave excellent yields, while indole derivatives of tryptophol, tryptamine, and indoleacetic acid were also efficiently arylated. Protected tryptophan derivatives and tryptophan‐containing di‐ and tripeptides were well tolerated, although more sterically demanding peptides gave only moderate yields. Structurally complex indole‐containing drugs and natural product derivatives underwent late‐stage arylation efficiently. Additionally, when reacting with indole, arene coupling partners prepared using different Ar‐DBT⁺ salts from easily accessible nucleophilic arenes, such as anisoles and other nucleophilic arenes bearing electron‐withdrawing groups, produced the required products in moderate to good yields, while highly complex arene substrates delivered slightly diminished yields.

A plausible mechanism was proposed, as shown in Scheme 22. Initially, palladacycle 67 is formed from N‐pyrimidylindole 64 and the Pd(II) catalyst. In parallel, visible‐light excitation of the photocatalyst generates an aryl radical 68 from aryl‐dibenzothiophenium salt 65. The aryl radical 68 is then trapped by 67 to give palladium intermediate 69, which is oxidized by the high‐valent Ir photocatalyst to form 70, thereby closing the photoredox cycle. Finally, the arylated product 66 is obtained by reductive elimination of 70, which also regenerates the Pd(II) catalyst.

In 2022, P.G. Cozzi and co‐workers reported a visible‐light‐driven metallaphotoredox method using a meso‐2‐methoxynaphthalenyl‐BODIPY (BDP) dye as an efficient organic photocatalyst for palladium‐catalyzed C─H arylation reactions (Scheme 23). Initially, they used 2‐(o‐tolyl)pyridine 71 and an aryl diazonium salt 72 as model substrates to optimize the reaction conditions. The optimal conditions involved utilizing 5 mol% of BDP and 10 mol% of Pd(OAc)₂ in methanol solvent. The reaction mixture was subsequently subjected to 23 W green LED illumination in an inert atmosphere at ambient temperature for 48 h. The target C─H arylation product was achieved in good yield under these improved conditions [89].

SCHEME 23 — C─H arylation of aryl diazonium salts.

After determining the optimal conditions, the authors studied the substrate scope using several substituted aryl diazonium salts. The reaction conditions worked well for both electron‐rich and electron‐deficient diazonium salts, producing the desired arylated products in moderate to good yields. The reaction could also be performed with various substrates such as substituted pyridines, amides, pyrazoles, ureas, and pyrimidines. These substrates underwent C─H activation and arylation; the yields ranged from low to moderate, depending on the directing group and substitution pattern. In some cases, side reactions like nucleophilic aromatic substitution (SNAr) with the solvent were also observed.

Finally, mechanistic studies were done to figure out how the reaction occurs, and a possible mechanism was suggested (Scheme 24). Upon green‐light irradiation, the BODIPY dye is excited to its triplet excited state (BDP*), which undergoes oxidative quenching by the aryl diazonium salt 72, generating an aryl radical 68 and the oxidized photocatalyst species. Meanwhile, the substrate 71 undergoes palladium‐mediated C─H activation, forming a palladacycle intermediate 74. The generated aryl radical 68 then intercepts this palladium intermediate 74 to produce a Pd(III) species 75, which is further oxidized to Pd(IV) 76. Finally, reductive elimination from the Pd(IV) intermediate 76 affords the aryl‐substituted product 73 while regenerating both the Pd(II) catalyst and the BODIPY photocatalyst, completing the catalytic cycle.

In 2023, Nidhi Jain and co‐workers developed a visible‐light‐promoted photoredox/palladium‐catalyzed site‐selective arylation and acylation of N‐protected carbazoles 14b (Scheme 25). They began their study using 9‐(pyrimidin‐2‐yl)‐9H‐carbazole and phenyl diazonium trifluoroborate 72 as model substrates for arylation. The optimized conditions for arylation involved 2 mol% of Eosin Y, 10 mol% of Pd(OAc)₂, and 2.0 equivalents of K₂CO₃ in MeCN under blue LED and nitrogen atmosphere at room temperature for 36 h [81].

SCHEME 25 — C─H arylation of N‐protected carbazoles.

After optimizing the reaction conditions, the authors explored the substrate scope using various substituted diazonium salts. Both electron‐donating and electron‐withdrawing diazonium salts afforded the corresponding products in low to good yields, whereas ortho‐substituted diazonium salts gave lower yields, likely due to steric hindrance. Quinoline‐ and naphthalene‐based diazonium salts failed to produce the desired products. Additionally, 3‐nitro‐9‐(pyrimidin‐2‐yl)‐9H‐carbazole did not yield the expected product. N‐pyridyl‐substituted di‐halo carbazole derivatives furnished the corresponding products in moderate yields. Unsymmetrical 3‐methyl‐9‐pyridyl carbazole afforded a mixture of regioisomers in good yield, while 2,7‐dibromo‐9‐pyridyl carbazole gave the desired product in low yield.

To understand the possible reaction pathway, the authors proposed a plausible mechanism (Scheme 26). Eosin Y was excited under blue LED irradiation to generate the photoexcited species Eosin Y*. This excited Eosin Y* acted as a strong reductant and transferred an electron to the diazonium salt 72 via a SET process, thereby generating the aryl radical 68 along with Eosin Y^• ⁺. Simultaneously, C─H activation of substrate 14b with Pd(OAc)₂ occurred in the presence of base to form the palladium complex. 22. The palladium complex 22 subsequently reacted with the aryl radical 68 to afford a Pd intermediate 78. At this stage, the two catalytic cycles converged, and a Pd intermediate 79 was generated through Eosin Y^• ⁺‐mediated oxidation of the Pd complex 78. Finally, reductive elimination from the Pd intermediate 79 furnished the desired arylation product 77 and regenerated the Pd(OAc)₂ catalyst.

In 2023, Purushothaman Gopinath and his team reported substituent‐controlled regioselective arylation of carbazoles 14a (Scheme 27). The study began with 9‐(pyrimidin‐2‐yl)‐9H‐carbazole and an aryl diazonium salt 72 as the model substrate. The optimized conditions were determined to be 10 mol% of Pd(OAc)₂ and 2.5 mol% of Ru(bpy)₃Cl₂ in methanol under argon at room temperature for 24 h, using a 44 W blue LED (Kessil) [90].

They then investigated the range of substrates for aryl diazonium salts, finding that substrates with ortho‐ and meta‐halo substitutions, as well as those with electron‐rich and electron‐withdrawing substituents, produced high to exceptional yields. Subsequently, they concentrated on unsymmetrical carbazoles for the regioselective arylation of different 2‐aryl‐substituted carbazoles under standard conditions, producing the compounds in good yields with a 1:1 solvent mixture of methanol and acetonitrile. Similarly, C‐2‐substituted carbazoles, such as 2‐halo‐ and 2‐trifluoromethyl‐substituted carbazoles, produced C‐8‐arylated compounds with great selectivity and good yields. Nevertheless, 2‐methyl‐substituted carbazole produced a 4:1 mixture of regio‐isomers, with the C‐8 regio‐isomer remaining the primary result. Notably, 2,4‐substituted carbazoles produced C‐1‐acylated compounds regio‐selectively in good yields, while electron‐donating 2‐substituted carbazoles produced C‐1‐arylated products. Furthermore, they observed that unsymmetrical carbazoles bearing substituents at the C‐2 position and aryl diazonium salts containing both meta‐ and para‐substituents afforded the desired diarylated products in good yields.

After that, to comprehend the mechanism of the arylation reaction, they carried out mechanistic investigations (Scheme 28). Based on these studies, they proposed a plausible mechanism in which palladium(II) acetate coordinates with carbazole 14a to form intermediate 82. In the photoredox cycle, the Ru(II) catalyst is irradiated with blue light to form an excited‐state Ru(II)* photocatalyst, which undergoes single‐electron transfer with the aryl diazonium salt 72 to generate an aryl radical 68 and a Ru(III) complex. At the same time, this aryl intermediate 68 reacts with intermediate 82 to form a Pd(II) intermediate 83. A Pd(IV) intermediate 84 is generated when the Ru(III) complex is reduced to regenerate Ru(II). Ultimately, the desired product 80 is obtained, and the Pd(II) catalyst is regenerated through reductive elimination from intermediate 84.

Dual eosin Y/Pd(II)‐catalyzed, green light‐mediated C(sp²)‐H arylation of N─H unprotected 2‐arylquinazolinones was developed by Ranjan Jana and co‐workers in 2024 (Scheme 29). Initially, the reaction was performed using 2‐phenylquinazoline‐4(3H)‐one 85 and 4‐chlorophenyl diazonium salt 72 as model substrates to optimize the reaction conditions. The optimized conditions were found to be 1 mol% of Eosin Y and 10 mol% of Pd(OAc)₂ in MeOH under an argon atmosphere, irradiated with green LED light at 35°C for 30 h [91].

SCHEME 29 — C(sp²)‐H arylation of N─H unprotected 2‐arylquinazolinones.

After optimizing the reaction conditions, the authors explored the substrate scope using 2‐phenylquinazoline‐4(3H)‐one and various substituted aryl diazonium salts. Both electron‐donating and electron‐withdrawing groups at the para‐position afforded the corresponding products in moderate to good yields; however, electron‐withdrawing groups gave lower yields compared to electron‐donating groups. The 4‐(trifluoromethyl)‐substituted diazonium salt provided a good yield, and in the absence of the photocatalyst, it afforded a higher yield than that obtained in its presence. Meta‐substituted diazonium salts gave the respective products in moderate to good yields. In contrast, ortho‐substituted diazonium salts afforded desired products in low to moderate yields. The authors then investigated substituted 2‐phenylquinazoline‐4(3H)‐ones with substituted aryl diazonium salts. Quinazolinones bearing electron‐donating groups provided moderate to good yields, whereas the nitro‐substituted quinazolinone did not produce the desired product. 4‐fluoro aryl diazonium salt gave a mixture of two products due to the nuisance effect. Furthermore, the 3,4‐difluoro aryl diazonium salt was converted in situ into the 3‐fluoro‐4‐methoxy derivative, which afforded the corresponding product in moderate yield.

Based on the experimental results and literature reports, the authors proposed a plausible reaction mechanism (Scheme 30). The substrate 85 was converted into its tautomeric forms 87 and 88. First, Eosin Y was photoexcited under irradiation to generate the excited state EY*. The excited EY* acted as a strong reductant and underwent single‐electron transfer (SET) with the aryl diazonium salt 72, generating an aryl radical 68 and EY^• ⁺. Meanwhile, Pd(II) coordinated with the quinazolinone 87, followed by C─H activation to form Pd intermediate 89. Then, this Pd intermediate 89 reacted with an aryl radical 29 to afford Pd intermediate 90. During the regeneration of the photocatalyst, the photoredox cycle merged with the palladium catalytic cycle through a SET process, in which Pd intermediate 90 was oxidized to Pd complex 91 by EY^• ⁺. Finally, Pd complex 91 underwent reductive elimination to furnish the desired product 86 with the regeneration of the Pd(II) catalyst.

In 2025, Kshirsagar and co‐workers reported a visible‐light‐mediated palladium‐catalyzed regioselective C8 arylation of 1‐(pyridin‐2‐yl)quinolin‐4(1H)‐ones 92 utilizing aryl diazonium salts 72 within a dual photoredox/Pd metal catalytic system (Scheme 31). This method allows for direct C─H functionalization under mild conditions, resulting in good to high yields of C8‐arylated quinolinone derivatives. To improve the reaction conditions, they started the study with 1‐(pyridin‐2‐yl)quinolin‐4(1H)‐one and 4‐chlorobenzenediazonium tetrafluoroborate as model substrates. After the optimization, the best conditions were found to be 10 mol% [Pd(OAc)₂]₃, 3 mol% of Eosin Y, and 0.2 mL TFA in 2.0 mL of methanol under green LED light at room temperature for 48 h. This gave the desired C8‐arylated product with a good to high yield [92].

SCHEME 31 — Regioselective C8‐arylation of 1‐(Pyridin‐2‐yl)quinolin‐4(1H)‐ones with aryl diazonium salts.

The substrate scope of aryl diazonium salts was examined under optimized conditions. Different halogen‐substituted diazonium salts worked effectively to generate the desired products with moderate to good yields. Electron‐donating substituents like ‐Me and ‐OMe gave higher yields. While strong electron‐withdrawing groups like ‐NO₂ and ‐CF₃ also gave the desired product in moderate yield. Moreover, 6‐methyl and 6‐chloro substituted 1‐(pyridin‐2‐yl)quinolin‐4(1H)‐one derivatives worked with the protocol, giving good to excellent yields. But ortho‐substituted and heteroaryl diazonium salts didn't react in the optimized conditions, probably due to steric hindrance.

The authors also proposed a plausible mechanism, which is shown in Scheme 32. First, Eosin Y gets excited by visible light to its photoexcited state EY*, which then undergoes a single electron transfer (SET) process with the aryl diazonium salt 72, generating an aryl radical 68 and the oxidized photocatalyst EY^• ⁺. At the same time, the Pd(II) catalyst coordinates with the quinolinone substrate 92 and activates the C─H bond at the C8 position, generating a Pd(II) intermediate 94. The generated aryl radical 68 then reacted with the Pd(II) intermediate 94 to make Pd(III) intermediate 95, which subsequently undergoes the SET process to generate high valent Pd(IV) intermediate 96 and photocatalyst, thereby closing the photoredox cycle. This intermediate 96 then goes through reductive elimination to make the C8‐arylated quinolinone product 93 and regenerate the Pd catalyst, completing the catalytic cycle.

4. Strategies for Allylation Reactions

The transformations discussed in this section represent a mechanistically distinct extension of classical allylic substitution, wherein the key advancement lies not only in the formation of π‐allyl–Pd intermediates, which are well established; but in the use of photochemically generated radical coupling partners that are not accessible in conventional two‐electron pathways. Accordingly, the transformations discussed in Schemes 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45 has been systematically organized based on the mode of generation of the allyl fragment and the radical species.

SCHEME 33 — Regioselective reductive allylation of imines.

SCHEME 34 — Enantioselective reductive allylic alkylation.

SCHEME 36 — Allylation of chiral 1,2‐amino alcohols and 1,2‐diamines.

SCHEME 38 — 1,3‐acyloxy allylation of aryl cyclopropanes with allyl esters.

SCHEME 40 — Three‐component synthesis of trifluoromethylated allylic alcohols.

SCHEME 42 — Multicomponent allylation and dienylation of styrene.

SCHEME 44 — Enantioselective allylic homo coupling reaction of 1,3‐dienes.

The direct regioselective reductive allylation of imines was reported by Chao‐Guo Yan and co‐workers in 2023. In their initial investigation, they used N‐(diphenylmethylene)benzamide 97 and allyl bromide 98 as model substrates to optimize the reaction conditions. The optimized conditions were found to be 2 mol% of Eosin Y, 2.5 mol% of Pd(OAc)₂, 5 mol% of DPPB, 2 equiv. of iPr₂NEt, and 2 equiv. of Na₂CO₃ in 2.0 mL DCM under blue LED irradiation at room temperature for 30 h (Scheme 33) [93].

Once the reaction conditions were optimized, the authors investigated the substrate scope with respect to various aryl imines, allyl halides, and benzyl chlorides. They discovered that aryl imines with electron‐donating, electron‐withdrawing, or electron‐neutral groups at the para‐position produced good to excellent yields. Similarly, substrates with meta‐ or ortho‐substituents gave moderate to excellent yields. Heteroarenes such as thiophene also yielded well. Polysubstituted allyl bromides gave good to excellent yields. This protocol was also applicable to the allylation of imines using C─O electrophiles such as allylic esters, allylic carbonates, and allylic tosylates. Benzyl chlorides with different substituents at the ortho‐, meta‐ or para‐ positions provided excellent yields.

In 2023, Shouyun Yu and co‐workers reported an enantioselective reductive allylic alkylation enabled by dual photoredox/palladium catalysis. They started the reaction using allylic acetate 100 and tertiary alkyl bromide 101a as the model substrates to optimize the reaction conditions. The optimized conditions were found to be of 2.0 equivalents of Hantzsch Ester (HE) and 2.0 equivalents of Cs₂CO₃ in 4 mL MeCN on irradiation of 45 W blue LED under N₂ atmosphere at room temperature for 12 h with 2 mol % of the photocatalyst Ir(ppy)₂(dtbbpy)PF₆ and 2.5 mol % of Pd₂(dba)₃ with 6 mol % of (R)‐DTBM‐BINAP (L1) and the desired product 102 was afforded in a good to excellent yield with excellent regio‐ and enantioselectivities (Scheme 34) [94].

By maintaining optimal conditions, the authors first studied various disubstituted allylic acetates by alkylating them with tertiary alkyl bromides, which produced the desired products in moderate to high yields, good enantioselectivities, and excellent regioselectivities. Additionally, different electron‐donating and withdrawing groups were tolerated at various positions. Substrates with electron‐donor substitutions proved to be more reactive, yielding higher results. Polycyclic aromatic allylic acetates also participated in this reaction, although with lower yields. Besides methyl groups, the acyclic alkyl group of the acetate generally gave relatively higher yields compared to cyclic substitutions. Next, the authors explored the substrate scope for various tertiary bromides. The protocol was compatible with tertiary alkyl bromides bearing substituted phenyl groups with electron‐donating and withdrawing groups at different positions, yielding the desired cross‐coupling allylic products in moderate yields with excellent enantioselectivities and regioselectivities. Non‐aryl‐substituted tertiary alkyl bromides also gave moderate yields and good enantioselectivities. Additionally, reductive cross‐coupling products with secondary alkyl bromides were achievable, but only at lower temperatures (0°C).

Based on these mechanistic studies, this group proposed a plausible mechanism (Scheme 35), in which the excited‐state photocatalyst Ir(III)* is formed by the absorption of visible light from Ir(III) photocatalyst. This excited‐state photocatalyst Ir(III)* reductively quenched by the hydrogen evolution (HE) process generates a low‐valent Ir(II) complex. Further, the oxidative addition of alkyl bromide 101a to Pd(0) complex generated an alkyl‐Pd(II) intermediate 103, which then undergoes reduction by the Ir(II) complex to regenerate Ir(III) and Pd(0) complex, together with the corresponding radical 105. Meanwhile, Pd(0) complex oxidatively adds to the allylic acetate 100 to give a Pd‐π‐allyl intermediate 104. Then radical 105 gets trapped by 104 and forms Pd(III) intermediate 106. Finally, allylic alkylation product 102 is produced upon reductive elimination of 106 with Pd(I) complex. This Pd(I) complex undergoes the SET process by the Ir(II) complex or the HE radical cation to regenerate the Pd(0) complex. The authors noted that an excited‐state palladium‐catalyzed pathway cannot be completely ruled out and identified the cooperative photoredox‐palladium catalytic pathway as the dominant mechanistic route.

As illustrated in Schemes 33 and 34, the dominant strategy involves the formation of π‐allyl–Pd intermediates from allylic electrophiles such as allyl bromides or allylic acetates via oxidative addition to Pd(0). In these cases, the photocatalyst generates carbon‐centered radicals from benzyl chlorides or alkyl bromides through reductive single‐electron transfer. These radicals subsequently intercept the π‐allyl–Pd intermediates, forming high‐valent Pd(III)/Pd(IV) species that undergo reductive elimination to furnish the allylated products. While this pathway closely resembles classical Tsuji–Trost reactivity, the key distinction is the replacement of traditional nucleophiles with radical species, thereby significantly expanding the scope of coupling partners.

In 2024, Bernhard Breit and co‐workers developed light‐driven asymmetric palladium‐catalyzed allylation for the fast synthesis of chiral protected 1,2‐amino alcohols and 1,2‐diamines. Initially, benzyloxyallene 107 and α‐silyl amine 108 were used as a model substrate. The optimized conditions were 2.5 mol% of Pd₂(dba)₃, 6 mol% of L2, 1.0 equivalent of pyridinium p‐toluenesulfonate (PPTS), and 1 mol% of [Ir(ppy)₂dtbbpy]PF₆ in EtOAc under Ar atmosphere and blue light irradiation at room temperature for 16 h (Scheme 36) [95].

The scope was explored with various allenes. Substituted benzyloxyallene derivatives reacted with α‐TMS amines and produced the corresponding products in good yields with high regio‐ and enantio‐selectivity. Terminal alkyl chain–substituted alkoxyallenes yielded the respective products from moderate to good yields. Aryloxyallenes also gave the desired products in good yields. Chiral‐substituted alkoxyallenes reacted with ligand L3 and exhibited reversed diastereoselectivity, indicating that the reaction was controlled by the chiral catalyst. Multiple functionalized substrates delivered the corresponding products in moderate yields. 1,1′‐Disubstituted allenes also yielded products in moderate yields. Benzyloxydienes produced the desired products in moderate yields, while thioallenes remained unreactive. Aminoallenes showed good reactivity and enabled a streamlined synthesis of chiral vicinal diamine derivatives. Next, the amine substrate scope was examined. Both electron‐donating and electron‐withdrawing substituted anilines produced the corresponding products in moderate to good yields. The reaction of benzyloxyallene with secondary amines yielded free amino alcohols in moderate yields with high regio‐ and enantio‐selectivity, and no hydroamination products were detected. Anilines with functionalized alkyl chains reacted well and gave the respective products in moderate to good yields. α‐Silyl amines were well tolerated and yielded moderate results; however, enantioselectivity decreased. α‐Alkyl‐substituted α‐silyl amines provided α‐substituted amino alcohols as a mixture of two diastereomers. Substituted α‐silyl amines were also compatible with N‐phthalimide and benzyloxydiene substrates 110a, producing the corresponding products in moderate yields. No reaction was observed with benzimidazole and phthalimide substrates. Furthermore, several amino acids and drug derivatives were tested as substrates, and the corresponding products were successfully obtained.

A believable reaction pathway was proposed based on mechanistic investigations (Scheme 37) and DFT calculations. Initially, oxidative addition of the Pd(0) catalyst by pyridinium p‐toluenesulfonate (PPTS) generated a Pd–hydride species 112. Subsequently, ligand exchange occurred through selective insertion of benzyloxyallene 107 into the Pd─H bond, forming a π‐allylic Pd(II) intermediate 113. Meanwhile, photoexcited state Ir(III)* reacted with α‐silyl amine 108 to generate the α‐amino radical 114. This α‐amino radical 114 then combines with the π‐allylic Pd(II) intermediate 113 to afford the alkene‐coordinated Pd(I) species 115. Thereafter, Pd(0) intermediate 116 was formed through reduction by the Ir(II) species, which, upon further reduction, forms the desired product 109 and regenerates the Pd(0) species, thereby completing the catalytic cycle.

A related variant is shown in Scheme 36 from Schemes 33 and 34, where the allyl fragment is generated from allenes via Pd–H insertion to form π‐allyl–Pd intermediates. In this system, α‐amino radicals derived from α‐silyl amines through oxidative SET engage with the palladium intermediate. This example highlights that, although the mode of allyl generation differs, the fundamental reactivity still relies on radical capture by a Pd–allyl species.

Further diversification of radical precursors is demonstrated in Scheme 38, where radicals are generated through SET‐induced ring opening of aryl cyclopropanes. These ring‐opened radicals subsequently react with π‐allyl–Pd intermediates formed from allyl esters, illustrating the compatibility of this manifold with radicals derived from C─C bond cleavage processes.

In 2024, Ji Lu and team reported a synergistic photoredox and palladium‐catalyzed 1,3‐acyloxyallylation of aryl cyclopropanes 117 with allyl esters 118. To evaluate the efficiency of the reaction, an aryl cyclopropane and an allyl ester were selected as model substrates. The study revealed that the optimal reaction conditions consisted of 2 mol% 9‐mesityl‐3,6‐di‐tert‐butyl‐10‐phenylacridinium tetrafluoroborate as the photocatalyst, 2 mol% of Pd₂(dba)₃, 5 mol% of ligand L3 in a MeCN: DCE (1:1, 2 mL) solvent system, and 30 W blue LED irradiation at room temperature under an argon atmosphere, for 24 h (Scheme 38) [96].

The authors investigated the substrate range of aryl cyclopropanes after optimizing the reaction conditions. Aryl cyclopropanes bearing a methoxy group at the para, ortho, and meta positions delivered the desired products in good yields. Likewise, para‐alkyl‐ and phenyl‐substituted aryl cyclopropanes provided significantly higher yields than the unsubstituted counterparts. Furthermore, disubstituted aryl cyclopropanes containing methyl, methoxy, or halogen groups at the para‐ and meta‐positions afforded moderate yields. Similarly, aryl cyclopropanes bearing gem‐diethyl substituents or two different alkyl groups also gave moderate yields, although with a low diastereomeric ratio of 52:48. To further assess the generality of this protocol, a wide range of functionalized allyl esters was examined with aryl cyclopropanes. Allyl acetates bearing 2‐alkyl or 2‐functionalized alkyl substituents furnished the desired products in moderate to low yields, whereas 2‐phenyl allyl acetates containing electron‐neutral, electron‐donating, halogen, or electron‐withdrawing groups at the para‐position delivered the products in significant yields. In contrast, 2‐naphthyl and 3‐phenyl allyl acetates afforded the desired products in poor yields. Additionally, cinnamic acid and its derivatives, as well as allyl esters bearing various para‐substituents, produced the corresponding products in low to moderate yields.

Based on mechanistic studies, the authors proposed a plausible mechanism (Scheme 39). Initially, Pd(0) undergoes oxidative addition with the allyl ester 118 to form intermediate 120 along with the corresponding counter anion 121. At the same time, the photocatalyst PC is excited by visible light to generate the excited state PC*, which undergoes a single‐electron transfer (SET) with the aryl cyclopropane 117 to produce the reduced species PC^•− and intermediate 122. The counter anion 121 then acts as a nucleophile, promoting the ring opening of intermediate 122 to afford intermediate 123. Subsequently, intermediate 123 undergoes an outer‐sphere nucleophilic C─C coupling, generating a Pd(I) species intermediate 124. Finally, intermediate 124 is reduced by PC^•− to furnish the final product 119 and regenerate the Pd(0) photocatalyst.

In 2025, Xiaoming Zhao and co‐workers reported a three‐component dual photoredox/palladium‐catalyzed reaction of vinyl cyclic carbonates (VCCs) 125, olefins 126, and the Langlois reagent (CF₃SO₂Na) 127 to synthesize highly substituted trifluoromethylated allylic alcohols 128 with excellent regio‐ and stereo‐control, including sterically congested quaternary carbons (Scheme 40). They start the reaction with vinyl cyclic carbonate, 1,1‐diphenylethylene, and CF₃SO₂Na as model substrates. By optimization, they found optimal conditions as 1 mol% of [Ir(ppy)₂(dtbpy)]PF₆, 2.5 mol% of Pd₂(dba)₃, 6 mol% of S‐BINAP, and 2 equiv. of KH₂PO₄ in 2 mL MeCN at room temperature under blue LEDs (450 nm) for 24 h under N₂ atmosphere, giving high Z/E selectivity and good to excellent yields [97].

Under optimized conditions, various vinyl cyclic carbonate derivatives such as para‐ and meta‐electron‐donating or ‐withdrawing groups yielded moderate to excellent amounts with >20:1 Z/E selectivity. Ortho‐substituted, dihalogenated, and heteroaryl (e.g., thiophen‐2‐yl) VCCs were tolerated, whereas non‐aryl VCCs did not produce the desired product. Among alkenes, 1,1‐diaryl alkenes showed the best results with high yields. Heteroaryl, aryl/alkyl, or dialkyl alkenes were compatible but with lower yield or selectivity, while mono‐substituted styrenes did not form the desired product.

Based on mechanistic studies as shown in Scheme 41, the authors proposed a plausible reaction pathway. Visible light excites Ir(III) to Ir(III)*^, which is reductively quenched by CF₃SO₂Na 127 to generate a CF₃ ^• radical 129 and Ir(II) complex. Then CF₃ ^• 129 adds to the disubstituted alkene 126 to form radical intermediate 130. On the other hand, Pd(0) undergoes oxidative addition to the VCC 125, followed by decarboxylation to form a π‐allyl‐Pd(II) complex 131. This complex 131 reacts with radical 130 and forms the intermediate 132, which undergoes reductive elimination, and the desired product 128 is formed along with the Pd(I) complex. Ir(II) complex then reduces the Pd(I) complex to regenerate Ir(III) and Pd(0) complexes via the SET mechanism, which completes the dual catalytic cycle.

In Scheme 40, a more complex three‐component system is observed, wherein vinyl cyclic carbonates generate π‐allyl–Pd intermediates via oxidative addition followed by decarboxylation. Concurrently, CF₃ radicals generated from CF₃SO₂Na undergo initial addition to alkenes, producing secondary carbon radicals that are then captured by the palladium intermediate. This cascade sequence underscores the ability of photoredox catalysis to orchestrate multistep radical generation prior to Pd‐mediated bond formation.

A conceptually related yet more advanced multicomponent strategy is presented in Scheme 42. In this system, the allyl fragment is generated through Pd‐mediated processes, while the radical partner arises from photoredox activation, followed by sequential radical addition and Pd interception steps. This transformation represents an extension of the cascade‐type manifold, wherein multiple bond‐forming events are integrated into a single catalytic sequence, enabling the construction of more complex molecular architectures.

Using propadiene as a coupling partner, Breit and co‐workers reported a palladium metallaphotoredox dual‐catalyzed procedure for the multicomponent allylation and dienylation of styrene derivatives in 2025 (Scheme 42). In order to maximize the reaction conditions, propadiene 133, 1,1‐diphenylethylene 134, and an isopropyl‐substituted dihydropyridine (DHP) radical precursor 135 were initially selected as model substrates. 7.5 mol % of Pd(OAc)₂ with 9 mol % of Xantphos as a ligand, 0.5 mol % of [Ir(ppy)₂(dtbbpy)]PF₆ as a photocatalyst, and 5 mol % of 4‐chlorobenzoic acid in toluene under blue LED irradiation at ambient temperature for 16 h in an argon environment were the optimum conditions for the allylation pathway. The intended allylic product was produced in excellent yield with outstanding chemoselectivity under these circumstances. In order to provide the dienylated product in good yield and a chemoselectivity greater than 20:1, a modified ligand and acid system was needed for the dienylation pathway. This system used (2‐furyl)₃P as the ligand and 4‐methoxypyridinium tosylate as the Brønsted acid additive [98].

First, the substrate scope was assessed in relation to the precursors of DHP radicals. Numerous secondary alkyl radicals, including cyclopropyl, benzyl, and heteroaryl‐derived radicals were effectively integrated and typically produced both allylic and dienylic products in moderate to good yields. The dual catalytic system was shown to be robust by the good tolerance of functional groups such as carbazoles, amides, indoles, acetals, and protected alcohols. In this reaction, benzoyl radicals participated without any difficulties. However, modest yields were obtained in the allylation direction by primary alkyl radicals, which were less efficient. The alkene partner's range was then investigated. Under both sets of circumstances, a variety of substituted 1,1‐diphenylethylenes containing halogen, electron‐donating, and electron‐withdrawing substituents were well‐tolerated. Additionally, the method was applied to styrene and α‐substituted styrene, which experienced effective three‐component allylation, while dienylation resulted in lowered efficiency. Despite having less regioselectivity, terminal allenes other than propadiene, such as phenyl allene and allene amides, were also suitable substrates.

After that, they carried out a mechanistic investigation through control tests, radical trapping investigations, deuterium labeling, and DFT computations to understand a plausible mechanism (Scheme 43). Upon being subjected to visible light, the DHP derivative 135 reductively quenches the Ir(III) photocatalyst, generating radical intermediate 138 and Ir(II) species. An intermediate stabilized diphenyl substituted radical 139 is produced when radical intermediate 138 joins the styrene derivative 134. The π‐allyl Pd(II) intermediates 140a and 140b are produced when the Pd(0) catalyst inserts into propadiene 133 after completing oxidative addition. The intermediates 140a and 140b are then reduced by Ir(II) to produce a Pd(I) complex 141a and 141b, which afterwards are reductively eliminated with the diphenyl substituted radical 139 in the outer sphere to generate the allylation product 136 and dienylation product 137 along with regeneration of Pd(0) complex. For both transformations, DFT studies confirmed that outer‐sphere reductive elimination at low‐valent Pd(I) species is preferred over inner‐sphere or high‐valent Pd routes.

In 2025, Weiwei and co‐workers reported a dual photoredox/palladium‐catalyzed enantioselective Heck/reductive allylic homocoupling of 1,3‐dienes 142 (Scheme 44). To optimize the reaction conditions, 1,3‐diene was chosen as the model substrate. The optimized conditions were identified as 5 mol% of Pd₂(dba)₃.HCCl₃, 20 mol% of phosphoramidite ligand L4, 2 mol% of Ir(ppy)₂(dtbbpy)PF, 1 equiv. of Cs₂CO₃, and 1.5 equiv of 4‐methylmorpholine in THF under blue LED light at 60°C for 22 h [99].

They start the substrate scope with different 1,3‐dienes containing electron‐donating or electron‐withdrawing groups at the para position of the phenyl ring, which gave an excellent yield of product with excellent enantioselectivity. Meta‐ and ortho‐substituted, 1,2‐disubstituted, or 3,4‐disubstituted phenyl rings containing 1,3‐dienes also provided good yields. Replacing the Bn group of amides with different benzyl groups also furnished the desired product in good yield. By replacing the R³ group, they also replace the methyl group with ethyl and n‐propyl groups.

To understand the mechanism, the author performed different experiments, and two pathways were proposed, as shown in Scheme 45. In the predominant pathway, Pd(0) undergoes oxidative addition with substrate 142 to form a Pd(II) intermediate 144, followed by migratory insertion with 1,3‐diene to generate an η³‐π‐allyl‐Pd(II) intermediate 145. Meanwhile, the iridium photocatalyst Ir(III) is excited by blue light to Ir(III)* and reduced by NMM to Ir(II), which transfers an electron to the η³‐π‐allyl‐Pd(II) intermediate 145, forming an η³‐π‐allyl‐Pd(I) intermediate 146 and regenerating Ir(III). The intermediate 146 exists in equilibrium with LPd(0) and an allyl radical 147. Finally, the allyl radicals 147 combine to give the final product 143. The product was also formed without a photocatalyst, indicating an alternative pathway. In this pathway, LPd(0) undergoes oxidative addition with substrate 142 to form 144, followed by migratory insertion to give 145. The intermediate 145 then absorbs blue light to form an excited state intermediate 148, which undergoes the LMCT (Ligand to metal charge transfer) process to regenerate LPd(0) and generate an allyl radical 147. Finally, the allyl radicals 147 recombine to produce the final product 143.

Finally, Scheme 44 represented a mechanistically distinct case in which the allyl fragment is derived from 1,3‐dienes through Pd‐mediated insertion (Heck‐type pathway), while the radical partner is generated independently under photoredox conditions. In contrast to the previous examples, this system likely proceeds through Pd(I)/Pd(II) manifolds involving radical–Pd convergence rather than classical π‐allyl–Pd intermediates, thereby expanding the mechanistic landscape of these transformations.

These distinct modes of allyl and radical generation have direct consequences for selectivity. In Schemes 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, regio‐selectivity largely follows ligand‐controlled trends typical of π‐allyl–Pd chemistry, although radical involvement often enhances branched selectivity, particularly with secondary and tertiary radicals. The multicomponent cascade processes in Schemes 40 and 42 further enable increased structural complexity, while the diene‐based system in Scheme 44 exhibits less predictable selectivity due to its deviation from classical pathways. Importantly, the use of more substituted radicals facilitates the construction of sterically congested centers, including quaternary carbons, which are difficult to access via traditional palladium catalysis.

Despite these advances, several limitations are evident. Primary radicals often display lower selectivity, whereas tertiary radicals are prone to side reactions such as β‐scission. Sterically demanding allyl fragments and heteroaryl substrates can reduce efficiency due to steric hindrance or catalyst deactivation. Additionally, many transformations, particularly those in Schemes 33 and 34, rely on carefully tuned phosphine or phosphoramidite ligands to achieve high regio‐ and enantio‐selectivity.

Overall, the reactions presented in Schemes 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45 demonstrate that dual palladium/photoredox catalysis enables allylic substitution through fundamentally distinct retrosynthetic disconnections, wherein radicals replace classical nucleophiles and engage palladium intermediates via single‐electron pathways. This synergy expands the range of accessible coupling partners, enables multicomponent and cascade processes, and introduces new selectivity paradigms, while also defining clear mechanistic and practical boundaries.

5. Strategies for Alkylation Reactions

The alkylation reactions have emerged as a powerful platform for forging C(sp³)–C bonds through the merger of radical generation and palladium‐mediated coupling. While conventional palladium catalysis is less effective and struggles to engage unstable or unactivated alkyl partners, often leading to issues such as β‐hydride elimination and limited substrate scope. In contrast, dual Pd/photoredox catalysis overcomes this by generating alkyl radicals efficiently.

A regio‐ and enantio‐selective decarboxylative allylic benzylation was reported by Shouyun Yu and co‐workers in 2022 (Scheme 46). They selected 2‐phenylacetic acid 149a and allylic acetate 100 as a model substrate to optimize the reaction conditions. For allylic acetate derivatives, the optimal condition employed 2.5 mol% of Pd₂(dba)₃ with 6 mol% chiral ligand L5, 2 mol% of [Ir{dF(Me)ppy}₂(dtbbpy)]PF₆ and 1.5 equivalents of K₂CO₃ in 2 mL DMA. The reaction scope was subsequently extended to vinyl epoxides 151, which required modified conditions using 2.5 mol% of Pd₂(dba)₃ with 6 mol% chiral ligand L6, 2 mol% of [Ir{dF(CF₃)ppy}₂(dtbbpy)]PF₆ and 1.5 equivalents of Cs₂CO₃ in 2 mL MeCN. Under 45 W blue LED irradiation for 12 h at 30°C, both catalytic systems efficiently furnished the desired products with high regio‐ and enantioselectivity [100].

The substrate scope revealed broad compatibility with both coupling partners. Electron‐donating substituents and alkyl groups on aryl acetic acids provided higher yields and enantioselectivities, whereas electron‐withdrawing substituents led to reduced efficiency and selectivity, affording products in moderate to good yields. Moreover, polycyclic and heteroaryl substrates were also well tolerated, while nonbenzylic acids were ineffective. Various aryl‐substituted allylic acetates accommodating ethers, halides, esters, alkynes, and heterocycles reacted smoothly providing desired products with high regioselectivity and enantioselectivity. Extension to vinyl epoxides enabled the formation of homoallylic alcohols with quaternary carbon stereocenters in moderate to good yields with excellent regioselectivity and good enantioselectivity.

Based on the radical trapping experiments, which indicated the involvement of a SET pathway, and prior studies on palladium metallaphotoredox catalysis, a plausible mechanism was proposed (Scheme 47). First, the carboxylate anion 153 formed from aryl acetic acids 149a quenches the excited photocatalyst Ir(III)* reductively and generates Ir(II) species with benzylic radical 154. Simultaneously, Pd(0) undergoes oxidative addition with allylic ester 100, affording π‐allyl‐Pd(II) intermediate 155, capturing benzyl radical 154 to give Pd(III) species 156. Subsequent reductive elimination delivers the benzylated product 150 and Pd(I) intermediate, which is reduced by Ir(II) to regenerate the active Pd(0) catalyst and the photocatalyst.

As shown in Scheme 46, a representative strategy involves decarboxylative activation of aryl acetic acids to generate benzyl radicals via single‐electron transfer. This transformation represents a canonical metallaphotoredox allylic alkylation manifold.

A mechanistically distinct pathway is illustrated in Scheme 48, where α‐amino acids serve as radical precursors via decarboxylation under photoredox conditions. This strategy highlights the ability of dual catalysis to access allyl–Pd intermediates without prefunctionalized allylic electrophiles.

In 2022, Breit and co‐workers reported a highly regio‐, diastereo‐, and enantio‐selective decarboxylative hydroaminoalkylation of dienol ethers enabled by a dual palladium/photoredox catalytic system (Scheme 48). This strategy combines palladium catalysis with photoredox activation to achieve intermolecular hydroaminoalkylation of electron‐rich dienol ethers 110b using α‐amino acids 157 as radical precursors. To identify the optimal reaction conditions, the authors initiated their study using N‐phenyl‐substituted phenylalanine and 2‐benzyloxydiene as model substrates under visible‐light irradiation. After systematic screening of photocatalysts, palladium sources, ligands, and additives, the optimized conditions were determined to be 5‐7 mol% of [(η³‐cinnamyl)PdCp], 12 mol% of ligand L3, and 1 mol% of the [Ir(ppy)₂(dtbbpy)]PF₆ in acetone with 3,5‐bis(trifluoromethyl)benzoic acid 159 as an additive under blue LED irradiation at room temperature. Under these conditions, the desired vicinal amino ether product was obtained in high yield with excellent regioselectivity (>19:1 rr), good diastereoselectivity (up to 6.7:1 dr), and outstanding enantioselectivity (up to 97% ee) [101].

The authors explored the substrate scope of α‐amino acids. A wide range of N‐aryl substituted natural and unnatural amino acids participated smoothly in the reaction, affording the corresponding vicinal amino ethers in moderate to excellent yields while maintaining high levels of regio‐, diastereo‐, and enantio‐selectivity. Amino acids bearing electron‐donating or electron‐withdrawing substituents on the aromatic ring were well tolerated. Importantly, substrates containing functional groups such as ester, nitrile, ether, thioether, hydroxyl, triazole, and alkene moieties also transformed efficiently. Furthermore, tyrosine and tryptophan derivatives possessing unprotected phenolic and indole groups were compatible with the reaction conditions, highlighting the remarkable functional group tolerance of the methodology. The scope of dienol ether coupling partners was also examined. Various substituted 2‐alkoxydienes reacted efficiently with α‐amino acid derivatives, affording the desired products in good to excellent yields with high regio‐ and enantio‐selectivity. Dienol ethers bearing different aryl or alkyl substituents were well tolerated, and the reaction could be performed on a preparative scale without significant loss in selectivity. Notably, the method also enabled the synthesis of structurally complex molecules containing fragments derived from natural products and pharmaceuticals, demonstrating its potential utility in late‐stage functionalization.

The author proposed a plausible mechanistic pathway as shown in Scheme 49. The reaction is initiated when the palladium precatalyst, in the presence of phosphoramidite ligand L7, is converted into the active Pd(0) species. From this point, two closely related pathways operate for the generation of the Pd(II)‐hydride species 161. In one pathway (path a), Pd(0) undergoes oxidative addition with the external carboxylic acid 159 to form a Pd(II)‐hydride species 160, which can then exchange ligand with the amino acid 157 to give Pd(II)‐hydride species 161. In the alternative pathway (path b), Pd(0) directly reacts with the amino acid 159 via oxidative addition to generate the same Pd(II)‐hydride species 161 without the need for prior acid activation. Once this common Pd(II)‐hydride species 161 is formed, the diene 110b coordinates to 161, and a reversible hydropalladation takes place, furnishing the key π‐allyl‐Pd(II) intermediate 162. At the same time, under light irradiation, the photocatalyst is excited to form Ir(III)* complex and promotes a single electron transfer process, enabling decarboxylation and generating an α‐amino radical which combines with the π‐allyl‐Pd(II) intermediate 162 in a rebound manner to form a Pd(III) species 164. This is followed by reductive elimination to form the desired hydroaminoalkylated product 158 and produces a Pd(I) species. Finally, the Pd(I) species is reduced back to Pd(0) by the reduced photocatalyst through another single electron transfer step, thereby closing both the palladium and photoredox catalytic cycles.

Further diversification is observed in Scheme 50, which describes two competing pathways: a polar crossover pathway involving reduction to a benzylic anion followed by nucleophilic attack on the Pd complex, and a radical pathway involving direct formation of a Pd(III) intermediate. This dual reactivity underscores the complexity of radical–Pd interactions in multicomponent systems.

In 2024, Zhiwei Jiao and his co‐workers reported a photoredox/palladium dual‐catalyzed dialkylation of azaaryl alkenes 165. In this study, azaaryl alkenes 165 and allylating reagents 166 were used as the reacting partners with CF₃SO₂Na 127 as radical precursors to optimize the reaction conditions. The optimized conditions were found to be 2 mol% of 4CzIPN, 2.5 mol% of PdCl₂, 3 mol% of L8, and 1.5 equivalents of Cs₂CO₃ in DCM under blue LED irradiation in an argon atmosphere for 12 h (Scheme 50) [102].

Using CF₃SO₂Na 127 as a model radical precursor, the authors examined the substrate scope for mononitrogen‐containing heteroarenes after the reaction conditions were optimized. They observed that the relevant compounds were produced in good yields from substrates with substituents at various positions (C3‐C6) of the pyridine ring. Sterically hindered quinolyl and isoquinolyl substrates gave good yields under the optimized conditions. Next, they examined polynitrogen‐containing heteroarenes and found that these substrates also provided good yields. The final product is also produced in good yield by a simple thiazole derivative. They found that substrates with various alkyl groups, as well as electron‐rich, electron‐deficient, and sterically hindered aromatic rings, all produced the desired products in good yields. Substrates containing i‐Pr, t‐Bu, cyclobutyl, Cp, Cy, and 4‐tetrahydropyranyl groups produced good yields. They also noticed that substrates containing an acidic Boc N─H unit continued to yield well. The reaction with cinnamyl carbonate yielded an excellent linear product. After successfully synthesizing quaternary carbon centers, the authors focused on constructing tertiary carbon centers. When 2‐pyridyl styrene was used as the radical acceptor and t‐BuBF₃K as the alkyl radical precursor, the desired difunctionalization product was obtained in good yield. Due to the ready availability of carboxylic acids, they next explored simple aliphatic carboxylic acids 149b as radical precursors and obtained good yields. Tertiary and secondary acids gave the desired products in good to excellent yields, while primary carboxylic acids also produced the products in good yields.

Ultimately, the authors carried out a mechanistic investigation and proposed a plausible mechanism (Scheme 51). The photosensitizer 4CzIPN is activated by visible light, oxidizing CF₃SO₂Na 127 to produce a CF₃ radical 129. Through a standard Giese reaction, this radical 129 combines with the azaaryl alkene substrate 165 to generate intermediate 169. The reaction can then proceed in one of two ways. In Path A, the photosensitizer converts intermediate 169 to a benzylic anion 170. Complex 172 is created when benzylic anion 170 combines with an L8‐ligated palladium allylic intermediate 171. The configuration of the exocyclic enamine is crucial at this stage, particularly for diastereoselectivity. Finally, conventional allylic alkylation produces the final product 167, and the Pd(0) catalyst is regenerated. In Path B, a Pd(0)/Pd(II)/Pd(III)/Pd(I)/Pd(0) cycle operates. Here, 169 adds directly to the L8‐ligated palladium allylic intermediate 171 to form a Pd(III) intermediate 174. Unlike Path A, this pathway favors inner‐sphere reductive elimination to give the final product 167. The resulting Pd(I) species is then reduced back to Pd(0) by the photosensitizer, completing the catalytic cycle.

In contrast to the above allylic alkylation manifolds, Scheme 52 represents a mechanistically distinct reductive alkylation process. In this case, alkyl radicals are generated from ammonium salts via C─N bond cleavage under photoredox conditions. These radicals couple with imine substrates in the presence of palladium, proceeding through a non‐π‐allyl pathway to furnish alkylated amines. This transformation highlights the extension of metallaphotoredox catalysis beyond allylic substitution into more general alkylation reactions.

Chao‐Guo Yan and co‐workers reported in 2025 a photoredox/palladium dual‐catalyzed reductive alkylation of imines and ammonium salts via dual C─N bond cleavage (Scheme 52). In order to optimize the reaction conditions, an alkyl ammonium salt 175 and a representative imine substrate 97 were first chosen as model substrates. The ideal conditions, which included using 10 mol% of Pd(OAc)₂, 2 mol% of Na₂‐Eosin Y, and 12 mol% of BINAP under blue LEDs at room temperature in the presence of 1 equiv. of Na₂CO₃ and 1 equiv of iPr₂NEt, allowed for the effective synthesis of alkylated amine products 176 [103].

The scope of the substrate was then investigated with a range of ammonium salts 175 and imines 97. The desired alkylated amines have been generated in good to excellent yields by imines with electron‐donating, electron‐withdrawing, and electron‐neutral substituents on the aromatic ring. Additionally, halogen‐substituted imines also give good yields. Moderate to excellent yields were observed by both aryl‐ and alkyl‐substituted imines. Notably, fused ring systems, aromatic imines with aryl acyl, and heteroaryl acyl protective groups also showed high functional group tolerance under the reaction conditions.

Collectively, the reactions depicted in Schemes 46, 47, 48, 49, 50, 51, 52 demonstrate that dual palladium/photoredox catalysis enables alkylation through three principal mechanistic paradigms: (i) decarboxylative radical coupling with π‐allyl–Pd intermediates, (ii) Pd–hydride‐mediated migratory insertion followed by radical rebound, and (iii) radical relay processes involving polar crossover or direct Pd(III) pathways. Additionally, non‐allylic systems based on C─N bond cleavage further expand the scope of this strategy. These advances underscore the versatility of dual catalysis in enabling structurally diverse alkylation reactions under mild conditions, while also revealing challenges associated with controlling selectivity and reactivity across distinct mechanistic regimes.

6. Strategies for Esterification Reactions

The strategies outlined in this section highlight the versatility of dual palladium/photoredox catalysis in enabling diverse esterification and carboxylation transformations through distinct radical generation modes. Whether via acetoxy radicals derived from hypervalent iodine reagents, acyl radicals generated through oxidative decarboxylation of α‐keto acids, or alkyl radicals formed under visible‐light activation, these approaches demonstrate how single‐electron processes can be seamlessly integrated with palladium catalysis to access unconventional Pd oxidation states and reactivity patterns.

The photoinduced meta‐acetoxylation of phenylacetic acid derivatives was described by Maiti and coworkers in 2023. During their initial study, they were using phenylacetic acid 149a and PhI(OAc)₂ 177 as a model substrate to optimize the reaction condition, and the final optimized condition was found to be 10 mol% of Pd(OAc)₂, 20 mol% of N‐Cbz‐Gly‐OH, and 3 mol% of Eosin Y in 1 mL HFIP under irradiation of 23 W CFL at 30°C°C–35°C for 36 h (Scheme 53). Later, they found that both nitrile‐ and methoxy‐based compounds (178, 180, and 182) provided the best result [104].

SCHEME 53 — Photoinduced *meta*‐selective C─H oxygenation of arenes.

After optimizing the reaction conditions, the author next investigated the substrate scope, beginning with phenylacetic acid derivatives. They found that derivatives with different substituents yielded the desired meta‐acetoxylation products in moderate to good amounts, with excellent selectivity. When electron‐withdrawing groups are present at the para position, the yield is moderate. The highest yield and selectivity occur when a methyl group is at the meta position. Ortho‐substituted phenylacetic acid derivatives also produce good yields. Next, they examined the scope for biphenyl carboxylic acids and alcohols, which also gave good yields. Finally, they applied the optimized conditions to sulfonyl‐linked benzyl arenes and found these substrates also gave good yields with excellent selectivity. Lastly, they tested PhI(TFA)₂ as an alternative acetoxylation source, which only yielded a selectively meta‐hydroxylated product.

The authors conducted a detailed mechanistic investigation and proposed a plausible mechanism (Scheme 54). First, Pd(OAc)₂ first binds with the amino acid ligand N‐Cbz‐Gly‐OH to give the active Pd(II)‐ligand complex 184. The substrate 182 then coordinates through the directing group, positioning the meta‐C─H bond near Pd; at this stage, an acetate group assists in C─H cleavage via CMD‐type (concerted metalation‐deprotonation) activation, to release AcOH and form the coordinated Pd(II)‐substrate complex 185. Under visible light, this species 185 undergoes photoinduced cyclometallation to generate the palladacycle intermediates 186 and 187, which are crucial for meta‐selectivity and are the rate‐determining step. Meanwhile, Eosin Y absorbs light and participates in a SET process with PhI(OAc)₂ 177, generating an acetoxy radical 188. This radical then couples with the palladacycle intermediate 187 to give a Pd(III) intermediate 189, which is further oxidized within the photoredox cycle to a Pd(IV) intermediate 190. Subsequent reductive elimination forms the desired meta‐acetoxylated product 183 and regenerates Pd(II), completing the Pd(II)/Pd(III)/Pd(IV) cycle.

In 2024, Pradyut Ghosh and his co‐workers reported work on the use of α‐keto acids 2 for decarboxylative esterification of alcohols 191 (Scheme 55). The authors began their study on the decarboxylative esterification reaction, in which phenylglyoxylic acid 2 and 4‐cyanophenol 191 were used as model reactants to optimize the reaction conditions. The optimized conditions were found to be 0.30 mmol of NaHCO₃, 2.5 mol% of [Ir{dF(CF)₃ppy}₂(dtbbpy)]PF₆, and 5 mol% of (4,4’‐dtbbpy)PdCl₂ in 1.5 mL of DMSO, irradiated under a 456 nm blue LED for 24 h [105].

After establishing the optimized conditions, the authors investigated the substrate scope of various acids and alcohols. They first investigated aromatic alcohols with various functional groups, such as electron‐donating substituents (H, Me, OMe, piperazyl), electron‐withdrawing groups (Ph, NO₂, CHO, COMe), and halide substituents at the para‐position. Similarly, the corresponding compounds were generated in moderate to good yields by phenols with electron‐rich and electron‐deficient groups at the meta‐ and ortho‐positions. In addition, disubstituted benzenes, naphthalene, indanone, and TPE dye‐based alcohols also delivered the desired products in good to excellent yields, while heterocyclic alcohols furnished the products in good yields. Notably, aliphatic alcohols gave lower yields than benzylic alcohols. Furthermore, the scope of the α‐keto acid components was examined using 4‐cyanophenol as the model substrate and a broad range of keto acids bearing electron‐rich substituents at the para‐, meta‐ or ortho‐ positions provided moderate to good yields. Dimethyl‐substituted, bicyclic naphthalene and heterocyclic thiophene derivatives also afforded the corresponding products in good yields.

The authors conducted a detailed mechanistic investigation and proposed a plausible reaction pathway involving two distinct palladacycle routes (Scheme 56). In path A, the alcohol 191 first undergoes oxidative addition to a Pd(0) species to generate a Pd(II) intermediate 193. Subsequently, Ir(III), upon excitation, forms Ir(III)*, which undergoes the SET process with α‐keto acid 2 to form acyl radical 5 and Ir(II) species. This radical 5 adds to Pd(II) intermediate 193 to produce a Pd(III) intermediate 194. This species generates another Pd(II) intermediate 196 along with Ir(III), through the SET process with Ir(II) species, thereby completing the photocatalytic cycle. The Pd(II) intermediate 196 finally undergoes reductive elimination to furnish the desired product 192 while regenerating the Pd(0) species, thereby completing the catalytic cycle. In path B, the Pd(III) intermediate 194 is formed in a similar way as in path A, and it directly undergoes reductive elimination to afford the oxidative decarboxylative ester product 192 along with Pd(I) species 195. This intermediate 195 is then reduced by a SET process, restoring both the Ir(III) photocatalyst and the Pd(0) intermediate, thus enabling continuation of the catalytic cycle.

In 2025, Jiawang Liu and team reported an enantioconvergent carboxylation using CO₂ of racemic heterobiaryl halides 198 enabled by a photoredox/palladium dual catalytic system. The study initially employed racemic 1‐(2‐bromonaphthalen‐1‐yl)isoquinoline 198, 1‐bromohexane 101b, and CO₂ 199 as the model substrates. The optimized reaction conditions employed 5 mol% of Pd(acac)₂, 6 mol% of L9, 5 mol% of 4CzIPN, 3.0 equivalents of iPr₂Net, 3.0 equivalents of Cs₂CO₃, 1.0 equivalents of LiNTf₂, and 50 mg of 4Å molecular sieves in 0.05 M DMA under 1 atm of CO₂ and 455 nm blue LED irradiation at 16°C for 24 h. (Scheme 57) [106].

SCHEME 57 — Enantioconvergent carboxylation using CO₂ of racemic heterobiaryl halides.

After optimizing the reaction conditions, the authors explore the substrate scope with various alkyl bromides. Chain‐substituted aryl bromide gave the corresponding axially chiral esters in good yield and excellent enantioselectivity. Alkyl bromide bearing different functional groups also afforded the desired esters with good yields and excellent enantioselectivity. This method further provides diesters with a good yield while maintaining excellent enantioselectivity. In addition, heteroarenes delivered the corresponding products in good yield and excellent enantioselectivity, and drug fragments were well tolerated under the reaction conditions. Subsequently, the authors investigated heterobiaryl bromides or triflates with 1‐bromo‐4‐methoxybutane. Substituents at the fourth & fifth positions on the naphthyl ring did not interfere with the reaction and furnished the desired products in good yield with excellent enantioselectivity. Bulky bromobenzene also gave a good yield and exhibited a high level of asymmetric induction. Moreover, substitution at the fourth, fifth, and sixth positions of the quinazoline ring afforded corresponding products in moderate to good yield with excellent enantioselectivity.

Based on mechanistic studies and literature reports, the authors proposed a plausible mechanism (Scheme 58). The Pd(II) precatalyst is initially converted into the active Pd(0) species, which then undergoes oxidative addition with the racemic heterobiaryl (pseudo)halide 190 to form cyclopalladium Pd(II) intermediates (201 and 201’). These intermediates are able to undergo continuous epimerization, thereby facilitating a dynamic kinetic asymmetric transformation under the control of the chiral ligand. As direct carboxylation of these species is not favored due to a high energy barrier, a single‐electron transfer event is promoted by the photoexcited catalyst PC^•−, generating Pd(I) intermediates (202 and 202’), while the epimerization process remains operative to ensure stereochemical induction. Subsequently, these Pd(I) intermediates (202 and 202) participate in coordination and migratory insertion with CO₂ to afford the corresponding carboxylated Pd(I) species 203. This intermediate is then efficiently intercepted by the alkyl bromide 101b via an SN² substitution step to deliver the ester product 200, which helps suppress racemization of the transient chiral carboxylate. In the final stage, the Pd(I) species is reduced back to Pd(0), thereby regenerating the active catalyst and closing the catalytic cycle. This approach highlights the merger of radical generation with chiral palladium catalysis, enabling CO₂ incorporation and affording axially chiral products with high enantioselectivity. The utilization of CO₂ as a C1 feedstock underscores the potential of such dual catalytic systems.

7. Strategies for Cross‐Coupling Reactions

The transformations involved in this section describes non‐classical cross‐coupling pathways by merging radical generation with unconventional Pd redox cycles, thereby overcoming the intrinsic dependence of traditional Pd catalysis on two‐electron oxidative addition and the lack of selectivity in photoredox‐only radical processes.

A palladium acetate and Mn‐based photoactive coordination polymer (called AnM‐CP) catalyzed approach for cross‐coupling reactions of olefins 126 with aryl diazonium salts 72 was developed by Hongzu Xing and coworkers in 2022, as shown in Scheme 59. AnM‐CP was initially synthesized using a solvothermal method, and then it was used as a photocatalyst. Styrene and 4‐bromobenzenediazonium tetrafluoroborate were used as model substrates for the reaction, which was conducted at room temperature under blue LED (32 W) irradiation. The optimized conditions employed diazonium salt and styrene in the ratio 1.5:1, delivering moderate to excellent yields under a nitrogen atmosphere with 3 mol% of both AnM‐CP and Pd(OAc)₂ in DMF. Further investigation revealed that the dual‐catalytic system remained efficient for seven consecutive cycles, and the heterogeneous photocatalyst (AnM‐CP) could be reused without separation of CP and Pd catalysts [107].

SCHEME 59 — Cross‐coupling reaction of olefins with aryl diazonium salts.

This method showed broad substrate scope. Aryl diazonium salts with diverse substituents and various olefins coupled efficiently, giving moderate to excellent yields. Ortho‐ and meta‐substituted methyl groups performed better than para‐analogues. Aryl diazonium salts reacted smoothly with heteroarenes that contained O, S, or N; the sequence of decreasing reactivity was furan > thiophene > pyrrole. Furthermore, compared to diazonium salts with electron‐donating substituents, those with electron‐withdrawing groups produced higher yields. A series of aryl iodides 205 also showed excellent yields for the reaction when utilized in place of aryl diazonium salts 72.

A plausible mechanism is outlined in Scheme 60. The photocatalyst AnM‐CP (or CP) generates an aryl radical 68 from diazonium salt 72 via the SET process when exposed to visible light. Simultaneously, Pd(II) undergoes reduction at the catalyst surface to form active Pd(0) species through an interfacial electron transfer process, potentially involving a metallic cluster or a single metal atom. After the olefin 126 and Pd(0) species coordinate to form intermediate 207, an aryl radical 68 is inserted to generate a Pd(I) intermediate 208, which is oxidized to produce a Pd(II) intermediate 209, thereby regenerating the photocatalyst. An alternative pathway involving radical chain transfer from the oxidation of intermediate 208 by another diazonium salt may also contribute. Ultimately, the cross‐coupled product 204 is obtained through reductive elimination, with the regeneration of active Pd(0) catalyst.

A distinct feature of this system is the use of a photoactive coordination polymer (AnM‐CP) as a heterogeneous photocatalyst, enabling interfacial electron transfer to generate both aryl radicals and Pd(0) species concurrently. Unlike conventional Pd catalysis, where oxidative addition of aryl halides is rate‐limiting, aryl radicals are formed directly from diazonium salts and inserted into Pd–olefin complexes via a Pd(I) intermediate pathway. This radical insertion mode avoids classical trans‐metalation steps and allows efficient coupling under ambient conditions with catalyst recyclability, a feature absent in homogeneous Pd or photoredox‐only systems.

In 2025, Jian Lv and co‐workers reported a palladium/photoredox dual‐catalyzed decarboxylative C(sp³)‐C(sp³) cross‐coupling reaction between γ‐methylidene‐δ‐valerolactones (GMDVs) 210 and alkyl carboxylic acids 149c (Scheme 61). For optimization, GMDV and 9H‐fluorene‐9‐carboxylic acid were selected as model substrates. Optimized conditions were obtained under 370 nm LED irradiation at room temperature in a nitrogen atmosphere, using 5 mol% of Pd(PPh₃)₄, 2 mol% of [Ir{dF(Me)ppy}₂(dtbbpy)(PF₆), and 4.0 equiv. of K₂CO₃ and 0.1 M DMA solvent. Under these conditions, the desired product was formed in excellent yield within two hours [108].

SCHEME 61 — Decarboxylative radical C(sp³)‐C(sp³) cross‐coupling reaction of γ‐methylidene‐δ‐valerolactones.

With the optimized conditions, they started the substrate scope of GMDVs having electron‐donating, electron‐withdrawing, or neutral substituents on the aromatic ring, which gave moderate to good yields. Aliphatic GMDVs were less reactive, while halogen‐substituted derivatives provided moderate yields. Also, heterocyclic substrates performed well, and ester‐ or cyano‐substituted GMDVs also afforded high yields. A broad range of alkyl carboxylic acids also worked well, giving moderate to excellent yields. Tertiary acids showed lower efficiency, whereas secondary benzylic acids reacted smoothly. The method was further demonstrated in late‐stage functionalization, including bioactive molecules such as naproxen.

Based on mechanistic studies, the authors proposed a plausible mechanism (Scheme 62). Under visible light, Pd(0) promotes decarboxylation of GMDVs 210 to form Pd(II)‐1,4‐zwitterionic intermediate 212, which, upon protonation by the combined action of K₂CO₃ and the carboxylic acid 149c, gives allyl Pd(II) intermediate 213. Homolysis of 213 generates hybrid allyl Pd(I) radical 214, leading to an allyl radical 215 and Pd(I) species. In parallel, the carboxylic acid 149c is converted into its corresponding carboxylate anion 153, which then is oxidized by the excited Ir(III)* photocatalyst via a single‐electron transfer (SET) process or, less efficiently, by the Pd(I) species, leading to the formation of a benzylic radical 154. The SET pathway simultaneously generates an Ir(II) species, which rapidly reduces Pd(I) back to Pd(0), thereby closing both catalytic cycles. Finally, radical‐radical coupling between the allyl radical 215 and benzylic radical 154 forms the C(sp³)‐C(sp³) product 211.

This transformation is mechanistically distinct in that Pd directly participates in substrate activation prior to radical formation, generating a zwitterionic Pd intermediate that evolves into an allyl Pd species, which undergoes homolysis to release an allyl radical. In parallel, the photoredox cycle produces a second radical from carboxylic acids, culminating in radical–radical coupling rather than Pd‐mediated reductive elimination. This diverges fundamentally from conventional Pd cross‐coupling, where both partners are coupled on the metal center, and from photoredox‐only systems, where such synchronized dual‐radical generation with Pd redox closure is not achievable.

8. Miscellaneous Reactions

This category encompasses transformations that do not primarily deliver simple bond construction products (C─C or C─O) but instead enable functionalization, annulation, or structurally complex scaffolds, thereby distinguishing them fundamentally from earlier sections and also by mechanistic modes that are inaccessible to either conventional Pd catalysis or photoredox catalysis alone.

In 2022, Maiti and co‐workers reported a photoinduced regioselective olefination of arenes 216 and 217 through a Pd/photoredox catalytic system (Scheme 63). This strategy merges palladium catalysis with organic photocatalysis to achieve the Fujiwara‐Moritani oxidative olefination under mild conditions, avoiding the use of stoichiometric silver oxidants typically required in thermal protocols. The optimal conditions for this reaction were found to be 10 mol% of Pd(OAc)₂, 20 mol% of L10 ligand, and 3 mol% of fluorescein in HFIP solvent at 30°C‐35°C under visible‐light irradiation for 28 h. Using the model substrate, the optimized system delivered the olefinated product in excellent yield with excellent β/α selectivity (>25:1) [109].

SCHEME 63 — Regioselective olefination of arenes at proximal and distal sites.

The substrate scope demonstrated broad applicability with a variety of acrylate derivatives as olefin coupling partners, including substrates 217 bearing carboxylic acid, ketone, nitrile, phosphonate, and sulfone groups, which gave the corresponding olefinated products in good to excellent yields while maintaining high regioselectivity. Furthermore, the method proved effective for electron‐rich and electron‐deficient arenes, where monosubstituted arenes such as toluene, anisole, and chlorobenzene predominantly converted into para‐olefinated products, whereas nitrobenzene, trifluoromethyl benzene, and benzaldehyde preferentially converted to meta‐olefinated products. In addition, the protocol was compatible with a range of heteroarenes, including thiophene, furan, pyridine, imidazole, quinoline, indole, and carbazole providing the corresponding olefinated products with good regioselectivity. The synthetic utility of the transformation was further demonstrated through late‐stage functionalization of complex molecules and natural product derivatives, highlighting the robustness and versatility of this photoinduced olefination strategy. In addition to the non‐directed strategy, the authors also explored a directing‐group‐assisted approach to further control the regioselectivity of the olefination reaction. Substrates containing coordinating functional groups, such as amides, pyridyl, and other heteroatom‐containing moieties, were examined as potential directing groups to guide the palladium catalyst to specific C─H bonds. Under the optimized visible‐light photoredox conditions, these directing groups effectively coordinated to the palladium centre, facilitating site‐selective C─H activation and subsequent olefination. As a result, the corresponding ortho‐olefinated products were obtained in good yields with excellent regioselectivity. The directing strategy proved compatible with a wide range of substrates bearing electron‐donating and electron‐withdrawing substituents, demonstrating the versatility of the method. Moreover, heteroaromatic substrates containing intrinsic coordinating atoms also participated smoothly in the transformation, affording the desired products in moderate to good yields. This directing‐group‐assisted protocol highlights the advantage of combining coordination control with photoredox‐mediated catalyst regeneration, enabling efficient and selective C─H functionalization under mild reaction conditions.

A plausible mechanism was proposed based on experimental observations (Scheme 64). Upon visible‐light irradiation, the organic photocatalyst PC is excited to its photoactive state PC*. The reduction of PC* to PC^•− facilitates the oxidation of Pd(0) to Pd(II) under aerobic conditions. The Pd(II) species then undergoes electrophilic C─H activation of the arene 216 or 219, forming a palladacycle intermediate 221. Subsequently, olefin 217 coordination and migratory insertion generate the corresponding alkyl‐Pd intermediate 222, which undergoes β‐hydride elimination to furnish the olefinated product 223. The resulting Pd(0) species is then reoxidized by the photoexcited photocatalyst and molecular oxygen, thereby regenerating the active Pd(II) catalyst and completing the catalytic cycle.

This transformation delivers regioselective C─H olefinated arenes, contrasting with fragment‐coupling products. Unlike conventional Pd catalysis, which requires stoichiometric oxidants to regenerate Pd(II), the present system employs photoredox‐mediated aerobic reoxidation, enabling milder conditions, and improved sustainability.

In 2024, Feng Zhu and co‐workers developed a photoredox palladium‐catalyzed aminocarbonylation of glycosyl oxamic acids 224 with (hetero)aryl bromides 225 to afford aryl amide N‐glycosides 226 (Scheme 65). They began their study using glucosyl oxamic acid and 4‐bromo‐1,1’‐biphenyl as model substrates. The optimized conditions were identified as follows: 5 mol% of Pd(PhCN)₂Cl₂, 5 mol% of Xantphos, 2 mol% of Ir[dF(CF₃)ppy]₂(dtbbpy)PF₆ and 1.5 equivalents of K₂HPO₄ in ⁱ PrOAc:H2O(4:1) under N₂ atmosphere and 430‐435 nm blue LED (18 W) irradiation at 49°C for 6 h [110].

SCHEME 65 — Photoredox palladium‐catalyzed aminocarbonylations.

The substrate scope was explored using various aromatic electrophiles. Both electron‐donating and electron‐withdrawing substituted (hetero)aryl electrophiles underwent carbamoylation with glucosyl oxamic acid to afford the corresponding products in moderate to excellent yield. Substrates bearing unprotected hydroxyl and amino groups also participated in the reaction, delivering the desired product with low yield. Medicinally related heteroarenes such as indole, benzoxazole, pyridine, and benzothiazole were well tolerated and provided the corresponding products in low to excellent yield. However, benzyl bromide, 2‐(bromomethyl)naphthalene, and cinnamyl bromide did not produce the desired product. The authors then applied this protocol to commercially available biologically active molecules and pharmaceuticals, successfully generating desired products. They also extended this method to the late‐stage glycodiversification of amino acids or peptides bearing a phenyl bromide moiety on the side chain. Furthermore, the generality of various glycosyl donors was also investigated.

Based on literature reports and mechanistic studies, the authors proposed a plausible reaction mechanism (Scheme 66). First, Ir(III) is excited to Ir(III)* under blue LED irradiation, enabling a pivotal single electron oxidation of glucosyl oxamic acid 224 and generating glycosyl carbamoyl radical 228 along with the Ir(II) complex. In path A, the radical intermediate 228 is directly added to the Pd(0) species 229 to form a Pd(I) alkyl intermediate 230. Then the intermediate 230 underwent oxidative addition with the aryl bromide 225 to generate Pd(III) intermediate 231. This intermediate, upon reductive elimination, affords the desired product 226 and generates Pd(I) species 232. In path B, oxidative addition of the aryl bromide 225 to Pd(0) species 229 generated Pd(III) intermediate 233, succeeded by oxidation with carbonyl radical 228. Similarly to path A, reductive elimination of 233, gives the desired product 226 and Pd(I) species 232, which participated in single electron transfer with the Ir(II) complex, which is oxidized to Ir(III) complex via single electron reduction of Pd(I) species 223 to Pd(0) species 229, thereby completing the both catalytic cycles.

This system affords amide‐linked glycosides, introducing multiple bonds (C─N and C─C) in a single sequence. Conventional Pd catalysis would proceed via two‐electron oxidative addition/carbonylation, but cannot access carbamoyl radical pathways. Conversely, photoredox‐only catalysis could generate radicals but lacks controlled Pd‐mediated cross‐selectivity and bond assembly. The dual system uniquely enables Pd(I)/Pd(III) manifolds coupled with radical interception, leading to complex glyco‐conjugates.

In 2025, Purushothaman Gopinath and co‐workers reported a C─H olefination annulation reaction of aryl carboxylic acids 149d with acrylates 234 using O₂ as a green oxidant enabled by dual palladium organo‐photoredox catalysis (Scheme 67). Using p‐anisic acid ethyl acrylate as model substrates, the optimal condition was identified as 3 equivalents of K₂CO₃, 10 mol% of Pd(OAc)₂, 5 mol% of fluorescein, and 30 mol% of N‐Ac‐Val in HFIP solvent, enabling moderate yields and high regioselectivity [111].

SCHEME 67 — C─H olefination annulation of aryl carboxylic acids.

After optimizing the reaction conditions, a variety of aryl carboxylic acids and acrylates reacted efficiently to afford corresponding 3‐alkyl/3,3‐dialkyl‐substituted isobenzofuranone derivatives. Sterically hindered acrylates produced lactone products in good to moderate yields, while phenyl vinyl sulfone and diethyl vinyl phosphonate also gave moderate yields; however, acrylamide was unreactive. Both electron‐donating and moderately electron‐withdrawing substitutes were compatible, affording good to moderate yields. Benzoic acids bearing diverse functional groups gave good yields, whereas disubstituted variants yielded moderately. Disubstituted internal olefins reacted efficiently to give good yields, but cyclic acrylates showed no reactivity. Additionally, medicines with the carboxylic acid moiety were successfully functionalized at a later stage.

A plausible mechanism was suggested as shown in Scheme 68. The carboxylic acid 149d, upon deprotonation, forms the carboxylate anion 153, which gives a five‐membered palladacycle intermediate 236 by coordinating with the Pd(II) catalyst. After that, the olefin 234 migrates into this palladacycle 236 and coordinates to give 237, thereafter generating a palladacycle with seven members 238. Subsequent β‐hydride elimination affords the ortho‐olefinated adduct 239 along with a Pd(II) species, followed by reductive elimination to produce Pd(0). The synergistic action of the photocatalyst and molecular oxygen leads to the reoxidation of the resultant Pd(0) catalyst into the active Pd(II) form. In the meantime, the olefinated product 239 forms intermediate 240 by undergoing oxopalladation, and again, coordination with the Pd(II) catalyst forms 241. Finally, protodemetallation of this intermediate 241 furnishes the 3‐alkyl‐ or 3,3‐dialkyl‐substituted isobenzofuranones 235.

In contrast to all previous sections, this system furnishes annulated lactone frameworks via cascade C─H activation. The defining feature is intramolecular annulation, producing cyclic products rather than linear functionalized molecules, thereby representing a higher level of molecular complexity.

In 2026, Maiti & co‐workers reported a dual photoredox and Pd‐catalysis strategy for the site‐selective distal δ‐functionalization of unactivated C(sp³)‐H bonds (Scheme 69). With optimized conditions having 2‐Pyridinecarboxamide (N‐(1,1,3,3‐Tetramethylbutyl)‐2‐pyridinecarboxamide) 242, bis(pinacolato)diboron B₂Pin₂ 243 or diphenyl disulfane (Ph₂S₂) 244 as a model substrate and 10 mol % of Pd(OAc)₂, 20 mol % of 2‐Chloroquinoline, 5 mol % of fluorescein, MeCN or MeOH as a solvent at O₂ atm and white LED for 24 h or 28 h for borylation and thioarylation, respectively [112].

SCHEME 69 — Auxiliary‐directed δ C(sp³)‐H functionalization.

Under optimal conditions, this protocol can achieve δ‐functionalization with a variety of electronically diverse functional groups, including disulfides ranging from methyl to nitro and halogens at each aromatic position. Disubstituted disulfides also proved compatible with this method, producing moderate amounts of the desired δ‐functionalized products. Furthermore, the authors reported the capability of forming C─C bonds at the δ‐position using the same approach with Pd(OAc)₂, 2‐chlorolepidine, and DCE as the catalyst, ligand, and solvent, respectively, along with 5 mol % of fluorescein as the photocatalyst. The target δ‐C─H olefination product was obtained with several acrylates as coupling partners, yielding the desired products. However, long‐chain acrylates with chain lengths of 6, 12, and 22 were found to be inconsistent under the applied conditions. Additionally, other olefins besides acrylates failed to produce the desired δ‐C─H olefinated products, as the methodology was strictly limited to activated acrylate motifs.

This methodology provides remote δ‐functionalized product, which by conventional Pd catalysis struggles with such transformations due to limited site‐selectivity beyond proximal coordination, while photoredox‐only systems lack precise spatial control over radical functionalization. The advance with this dual system is that it integrates auxiliary‐directed Pd coordination with photoredox radical pathways, enabling site‐selective activation at distal positions.

9. Summary and Outlook

Over the past five years (2022–2026), there have been significant advancements in visible‐light‐driven dual palladium/photoredox catalysis. It has emerged as a powerful synthetic platform that integrates radical generation with organopalladium reactivity, enabling transformations beyond the reach of conventional Pd(0)/Pd(II) catalysis and standalone photoredox systems. Across the literature, this strategy has demonstrated clear advantages in mild reaction conditions, expanded substrate scope, and access to unconventional bond‐forming pathways, including radical–Pd interception, high‐valent Pd intermediates, and outer‐sphere coupling manifolds. These features have enabled diverse transformations ranging from cross‐coupling and functionalization to annulation and late‐stage modification.

Despite these advances, the literature reveals several persistent limitations. Mechanistic ambiguity particularly the distinction between closed catalytic cycles and radical chain pathways continues to hinder rational design. Substrate scope remains biased toward activated radical precursors, while unactivated alkyl fragments and remote C(sp³)–H sites are less developed. Control over regio‐ and enantio‐selectivity is still limited, especially in radical‐mediated processes. Notably, cross‐coupling and aminocarbonylation manifolds are comparatively underexplored, with only a limited number of general and modular protocols reported, highlighting a clear opportunity for future development.

Looking ahead, several research directions emerge. Achieving stereocontrolled radical processes, particularly asymmetric remote C(sp³)–H functionalization, represents a major unmet goal. Expanding cross‐coupling paradigms to include broader electrophile classes, unactivated alkyl partners, and multicomponent aminocarbonylation reactions could significantly enhance synthetic utility. The development of ligand platforms capable of stabilizing high‐valent Pd intermediates while imparting stereocontrol is especially critical. Furthermore, integration with electrophotochemical systems may provide improved control over redox events, while the use of earth‐abundant metal photocatalysts or organic dyes could address sustainability and cost concerns.

Equally important is improving compatibility with complex molecular architectures, enabling predictable late‐stage functionalization. Advances in scalable reactor design (e.g., flow photochemistry) and catalyst robustness will be essential for practical implementation. Overall, dual palladium/photoredox catalysis continues to push organic synthesis toward broad and selective transformations, and addressing these gaps will define its transition from a powerful academic tool to a widely applicable synthetic strategy.

Conflicts of Interest

The authors declare no conflicts of interest.

Acknowledgments

S. V., A. P., and Y. D. thank SVNIT Surat for the fellowship. M.M. thanks CSIR‐New Delhi for the fellowship. S.D. thanks SVNIT Surat for the research facility. M.P. thanks UGC‐Delhi for the fellowship. T.N. gratefully acknowledges the financial support from CSIR‐HRDG, India (Project File No. 02(0449)/21/EMR‐II). K. P. gratefully acknowledges the financial support from DST‐SERB, India (Project File No. CRG/2021/003497); CSIR‐HRDG, India (Project File No. 02(0454)/21/EMR‐II); and a seed grant received from CTUAP (F. No. B‐130/RO/CTUAP/2025/051). P. M. D. thanks ANRF‐NPDF (File No. PDF/2025/001041).

Biographies

Shivam Vispute was born in Gujarat, India. He received his B.Sc. degree in Chemistry from Sardar Patel University (V.P. & R.P.T.P. Science College, Anand) in 2021 and his M.Sc. degree in Organic Chemistry from Charutar Vidya Mandal University (Institute of Science & Technology for Advanced Studies & Research, Anand) in 2023. He qualified the GATE examination in 2023 and subsequently worked as a research associate in the CRO R&D Department at O2h Discovery, Ahmedabad. He is currently pursuing his Ph.D. in the Department of Chemistry at Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat, under the supervision of Dr. Togati Naveen.

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Arpan Patel was born in Navsari, Gujarat, India. He completed his bachelor's degree in chemistry in 2023 from Veer Narmad South Gujarat University (College of Applied Sciences and Professional Studies, Chikhli) followed by a master's degree in organic chemistry in 2025 from Veer Narmad South Gujarat University (V. S. Patel College of Arts & Science, Bilimora). He qualified for the Gujarat State Eligibility Test (GSET) in 2024 and the Graduate Aptitude Test in Engineering (GATE) in 2025. He is currently pursuing his Ph.D. research under the supervision of Dr. Togati Naveen in the Department of Chemistry at Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat.

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Mohan Mokariya was born in Porbandar, Gujarat, India. He completed his bachelor's degree in chemistry in 2020 from Maharshi Dayanand Science College ‐ Porbandar followed by a master's degree in organic chemistry in 2023 from Shri V. J. Modha College ‐ Porbandar. He qualified for the Gujarat State Eligibility Test (GSET) in 2023 and the Joint Council of Scientific and Industrial Research ‐ University Grants Commission National Eligibility Test (Joint CSIR‐UGC NET) in 2025. He is currently pursuing his Ph.D. research under the supervision of Dr. Togati Naveen in the Department of Chemistry at Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat.

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Shreeya Dave was born in Jamnagar, Gujarat, India. She completed her bachelor's degree in chemistry in 2022 from Bahauddin Science College, Bhakta Kavi Narsinh Mehta University followed by a master's degree in organic chemistry in 2024 from the Department of Chemistry, Sardar Patel University. After her post‐graduation, she joined O2h Discovery, Ahmedabad, as a Trainee Research Chemist in the CRO R&D Department, where she gained foundational industrial research experience. She is currently pursuing her Ph.D. under the supervision of Dr. Togati Naveen in the Department of Chemistry at Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat.

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Yash Dhaduk was born in Junagadh, Gujarat. He completed his Bachelor of Science in Chemistry in 2022 from Bahauddin Science College, Bhakta Kavi Narsinh Mehta University. He later completed his Master of Science in Organic Chemistry in 2024 from the Department of Chemistry, Sardar Patel University, graduating as a gold medalist. During his master's studies, he qualified for both the CSIR‐NET (2023) and the Gujarat State Eligibility Test (GSET, 2023). After his postgraduate degree, he joined SynZeal Research Pvt. Ltd., Ahmedabad, as a trainee research chemist in the API R&D department, where he gained practical research experience. He is currently pursuing his Ph.D. under the guidance of Dr. Togati Naveen at the Department of Chemistry, SVNIT, Surat, Gujarat.

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Maulik Pethani was born in Junagadh, Gujarat. He completed his Bachelor of Science in Chemistry in 2020 from Bahauddin Science College, affiliated with Bhakta Kavi Narsinh Mehta University. He went on to earn his Master of Science in Organic Chemistry in 2023 from the Department of Chemistry at The Maharaja Sayajirao University of Baroda. He qualified for the CSIR‐NET JRF examinations in 2024 and 2025, as well as the Gujarat State Eligibility Test (GSET) in 2024. Following his postgraduate studies, he joined SynZeal Research Pvt. Ltd., Ahmedabad, as a Research Associate‐I in the API R&D department, where he gained valuable hands‐on research experience. He is currently pursuing his Ph.D. under the supervision of Dr. Togati Naveen in the Department of Chemistry at SVNIT Surat.

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Prabhakara Madivalappa Davanagere received his master's degree in chemistry from VIT Vellore in 2016 and completed his Ph.D. in 2022 at VIT Vellore under the guidance of Dr. Barnali Maiti. He carried out postdoctoral research at the Tungai University with Prof. Ding‐yah Yang, supported by a NSTC Postdoctoral Fellowship, and is currently an ANRF‐National Postdoctoral Fellow at the Central Tribal University of Andhra Pradesh. His research focuses on organocatalytic asymmetric construction of enantioenriched polyheterocycles via aza‐Mannich and ring‐Opening desymmetrization of oxetan‐3‐amines: toward new drug‐like scaffolds.

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Kishor Padala received his master's degree in chemistry from Osmania University in 2009 and completed his Ph.D. in 2016 at IISER Pune under Prof. M. Jeganmohan. He carried out postdoctoral research at the Hebrew University of Jerusalem with Dr. Ahmad Masarwa, supported by a PBC Postdoctoral Fellowship. He began his independent career as an assistant professor at Vellore Institute of Technology (2018–2022) and is currently an assistant professor at the Central Tribal University of Andhra Pradesh. His research focuses on transition metal‐free oxidative coupling, photoredox catalysis, asymmetric synthesis, and natural product synthesis.

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Togati Naveen obtained his B.Sc. in chemistry from Kavitha Memorial Degree College, Khammam, and his M.Sc. in chemistry from Kakatiya University, Warangal. Later in 2017, he acquired his Ph.D. degree from IIT Bombay under the supervision of Prof. Debabrata Maiti. After postdoctoral studies at CSIR‐IICT Hyderabad, he joined the Department of Chemistry of Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat, as an assistant professor in 2019. His research interests are mainly focused on the development of new and sustainable synthetic methodologies.

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Contributor Information

Kishor Padala, Email: kishor.padala@gmail.com.

Togati Naveen, Email: togatinaveen123@gmail.com.

Data Availability Statement

Data Availability Statement does not apply to a review article.

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PERMALINK

Recent Advances in Dual Palladium Photoredox Catalysis

Shivam Vispute

Arpan Patel

Mohan Mokariya

Shreeya Dave

Yash Dhaduk

Maulik Pethani

Prabhakara Madivalappa Davanagere

Kishor Padala

Togati Naveen

ABSTRACT

1. Introduction

FIGURE 1.

FIGURE 2.

FIGURE 3.

FIGURE 4.

2. Strategies for Acylation Reactions

2.1. C(sp2)‐H Acylation Involving Directing‐Group‐Assisted Cyclopalladation Through CMD‐Type Pathways

2.1.1. Using Phenyl Glyoxylic Acids as Acyl Source

SCHEME 1.

SCHEME 2.

SCHEME 3.

SCHEME 4.

SCHEME 5.

SCHEME 6.

SCHEME 7.

SCHEME 8.

SCHEME 9.

SCHEME 10.

SCHEME 11.

SCHEME 12.

2.1.2. Using Aldehyde as Acyl Source

SCHEME 13.

SCHEME 14.

SCHEME 15.

SCHEME 16.

2.2. C(sp3)‐H acylation involving 1,n‐HAT pathways

SCHEME 17.

SCHEME 18.

SCHEME 19.

SCHEME 20.

3. Strategies for Arylation Reactions

SCHEME 21.

SCHEME 22.

SCHEME 23.

SCHEME 24.

SCHEME 25.

SCHEME 26.

SCHEME 27.

SCHEME 28.

SCHEME 29.

SCHEME 30.

SCHEME 31.

SCHEME 32.

4. Strategies for Allylation Reactions

SCHEME 33.

SCHEME 34.

SCHEME 35.

SCHEME 36.

SCHEME 37.

SCHEME 38.

SCHEME 39.

SCHEME 40.

SCHEME 41.

SCHEME 42.

SCHEME 43.

SCHEME 44.

SCHEME 45.

5. Strategies for Alkylation Reactions

SCHEME 46.

SCHEME 47.

SCHEME 48.

SCHEME 49.

SCHEME 50.

SCHEME 51.

SCHEME 52.

6. Strategies for Esterification Reactions

SCHEME 53.

SCHEME 54.

2.1. C(sp²)‐H Acylation Involving Directing‐Group‐Assisted Cyclopalladation Through CMD‐Type Pathways

2.2. C(sp³)‐H acylation involving 1,n‐HAT pathways