Catalyst-Free, Visible-Light-Triggered One-Pot Formation of Imidazole N‑Oxide Derivatives in H₂O/EtOH Medium: Investigation of Their Therapeutic Properties

Abstract

An innovative, astonishing, and nonphotocatalytic visible-light-mediated synthesis of imidazole N-oxide derivatives has been established in aqueous ethanol via formation of an electron donor–acceptor (EDA) complex under mild, sustainable conditions. UV–visible spectroscopy analysis verified the production of the EDA complex, while the cyclic voltammetry (CV) experiment showed the oxidizing and reducing nature of the reactants. The stoichiometric ratio of the donor and acceptor compounds in the EDA complex was estimated using Job’s plot, and the binding constant was estimated using the modified Benesi–Hildebrand equation. Mechanistic investigations and control experiments revealed a radical route, which was confirmed by TEMPO radical trapping tests, and the conversion of reactants to radical-trapped adducts was investigated using high-performance liquid chromatography (HPLC) analysis. The electrical properties and charge-transfer characteristics of the EDA complex were further confirmed by theoretical studies by applying TD-DFT calculations. This approach encouraged the synthesis of 56 imidazole N-oxide derivatives with acceptable to exceptional yields (up to 98%). The usefulness of the method was demonstrated by gram-scale synthesis, which yielded the desired product in 72% yield, and by scale-up experiments that examined yield variance across mmol-scale reactions. Green chemistry parameters were also determined, suggesting that this method generates fewer waste products and is more environmentally friendly. The preliminary biological evaluation of the produced compounds revealed that various derivatives have significant antioxidant, antidiabetic, and anti-inflammatory properties. Furthermore, cytotoxicity investigations against the WRL-68 cell line revealed that certain compounds have low cytotoxicity, indicating possible biological compatibility.

1. Introduction

The remarkable success of visible-light-mediated photoredox catalysts can be largely attributed to their low cost, mild reaction conditions, clean reactions, and minimal environmental impact. Most organic molecules cannot be readily activated by visible light; hence, the bulk of visible-light photocatalytic processes necessitate external photocatalysts. However, in recent years, there has been an increase in endogenous photoreactions that eliminate the need for extrinsic photosensitizers. In this inventive approach, each experiment utilizes an electron donor–acceptor complex (EDA), offering a notable impact in the domain of radical chemistry empowered by visible light. Robert Mulliken, in the year 1952, discovered the concept of the electron donor–acceptor (EDA) complex, which is basically the molecular aggregation of electron donor and electron acceptor molecules, which sometimes carry out the photoinduced single-electron transfer (SET) reactions without adding any external transition metal catalyst. Electron-deficient substrates like aldehydes act as the electron acceptors, whereas electron-rich substrates like amines, enamines, or enolates participate as the electron donor. Excitation of these EDA complexes by visible light facilitates the transfer of an electron from the electron-deficient center to the electron-rich center, which leads to the development of radical species followed by the generation of C–C, C–N, C–B, and C–S bonds.

Pharmacological and therapeutic fields of science have been appreciably impacted by heterocyclic chemistry, particularly the N-containing heterocycles, a significant class of molecules. In this perspective, five-membered heterocyclic rings containing nitrogen can be observed in the numerous chemicals that have biological activity. In the field of five-membered heterocycles, the imidazole scaffold displays an abundance of characteristics. Researchers have been inspired to create a significant number of advanced chemotherapeutic medicines by the strong medicinal properties of imidazole-related compounds. The amino acid histidine, vitamin B₁₂, a component of the DNA base structure, purines, histamines, and biotin belong to the very familiar human organisms whose fundamental framework is formed by the imidazole nucleus. Many natural or manufactured medicine compounds, including metronidazole, azomycin, and cimetidine, also have it in their structure (Figure ). Drugs that include imidazole have a wider range of applications in clinical medicine to treat different conditions. Additionally, derivatives of imidazole compounds display a wide range of bioactivities, including antimicrobial, antidiabetic, antiviral, antihypertensive, anticancer, anti-inflammatory, analgesic, and more. Thus, imidazole has been reasonably used as a common heterocycle in medicinal products and biological frameworks. In this context, imidazole N-oxides are a unique but relatively underexplored member of the imidazole family. The 21st century has seen a continuous increase in curiosity regarding physiologically active compounds with N-oxide or N-hydroxy imidazole motifs in their structures as well as benzoannulated equivalents of these compounds. These kinds of compounds include herbicides, chemical compounds with antiprotozoal , and antitumor , behavior. Imidazole N-oxide has not been extensively researched as a bioactive scaffold, in comparison to benzimidazole N-oxides, which have been examined as pharmacophores. Latest research studies have revealed that imidazole N-oxides may function as an adaptable synthetic intermediate, providing access to functionalized imidazoles, imidazolium salts, and imidazole-2-ylidenes. Imidazolium salts such as IMes HCl (1,3 bis-{2,4,6-trimethylphenyl}­imidazolium chloride) and IPr HCl (1,3-bis-{2,6 diisopropylphenyl}­imidazolium chloride) are a well-known precursor to N-heterocyclic carbenes (NHCs) through base-induced deprotonation and are often employed in organometallic chemistry as ligands and organocatalysts. Also, 1-hydroxy-4,5-dimethyl-imidazole 3-oxide exhibits its potential as a coformer in pharmaceutical cocrystals production. In addition to these, imidazole N-oxides have also spread their application in a variety of reactions, including heterocyclizations that result in fused heterocyclic systems, isomerization to corresponding imidazole-2-ones, [3 + 2]-cycloadditions, sulfur transfer reactions that result in imidazole-2-thiones, and cross-coupling reactions. These qualities emphasize how crucial it is to create effective and precise techniques for the synthesis of imidazole N-oxides.

1.

Application of imidazole derivatives and imidazole N-oxide derivatives.

To date, many researchers have developed various synthetic methods for producing imidazole derivatives (Scheme ). − Regretfully, the majority of them depend on quite severe reaction circumstances. These factors encompass exceedingly elevated temperatures, environmentally detrimental reagents and reactants, protracted durations, restrictions on a narrower range of substrates, and the occurrence of side reactions. However, most of these techniques can create the requisite imidazole N-oxide with an average yield of 80%. Thus, we are actively seeking a cheaper and more environmentally friendly procedure that can yield the product in the desired quantity. As far as we know, no publication in the literature demonstrates methods to prepare imidazole N-oxide derivatives in a greener approach under visible light-mediated conditions. Here, a worthwhile approach to produce derivatives of imidazole N-oxides via a ternary EDA complex has been described (Scheme ).

1. Previously Reported Studies on the Synthesis of Imidazole N-Oxide.

2. Our Approach toward the Synthesis of Imidazole N-Oxide.

2. Results and Discussion

To assess the feasibility of this reaction, optimization of the conditions was started, utilizing diacetyl monoxime (1), benzylamine (2a), and paraformaldehyde (3) as the model substrates. To bring out the best conditions, a wide range of visible lights of varying intensities (watts) and various solvents were used. Initially, the reaction was carried out at room temperature in ethanol as a solvent. But a moderate yield of the desired product was received, which did not reach the expectations. The experiment was begun with different solvents to obtain the product in the expected yield, allowing the reaction to be repeated for a variety of substrates. In this regard, the reaction was set up to run for 2 h at room temperature under the continuous irradiation of 2 × 9 W blue LEDs. Solvents dichloromethane (Table , entry 2) and acetonitrile (Table , entry 3) gave unsatisfactory results for the product, and the yield was not determined. Employing toluene as a solvent also yielded a poor result (21%, Table , entry 1) for the target product. Following these solvents, we used an aqueous ethanolic medium (H₂O/EtOH) as the solvent in a 2:1 ratio, and the results were certainly gratifying to us. This solvent ratio resulted in 98% (Table , entry 8) of the target product. The yield decreased to 75% when the water: ethanol ratio was changed from 2:1 to 1:1 (Table , entry 7). Methanol (Table , entry 4) and water (Table , entry 6) are individually further employed as solvents; however, they provide less appealing results than the aqueous ethanolic medium (H₂O/EtOH, 2:1, v/v). Hence, an aqueous ethanolic medium (H₂O/EtOH, 2:1, v/v) is the optimum solvent for this reaction to proceed in a high yield. The solvent optimization gracefully draws a justified choice for solvents for which the probable mechanistic pathway and nature of this photochemical reaction can be well-understood. Nonpolar and polar aprotic solvents such as toluene and dichloromethane afforded very poor yields, probably due to their incapability to stabilize the transient reaction intermediates formed under visible light irradiation. Also, acetonitrile, being a moderately polar solvent, is unable to form a hydrogen bond with the intermediates to stabilize them and carry out the forward reaction. Conversely, polar protic solvents such as ethanol and methanol appreciably increase the efficiency of the reaction by yielding 75–82% due to their ability to form hydrogen bonds and also to facilitate the proton-coupled electron transfer (PCET) process (explained in the mechanism part; Figure ), whereas water alone yields 65%, attributed to its hydrogen-bond forming ability and limitation of solubility of organic substrates. Particularly, a water/ethanol mixture solvent can increase the solubility of organic substrates and stabilize the intermediates by forming a strong hydrogen-bond network, providing a higher yield than the individual solvents, signifying the synergistic solvent effect. The solvent mixture of water/ethanol in a 2:1 ratio gives higher yields than that in a 1:1 ratio, which justifies the greater contribution of water to stabilize the intermediates.

1. Optimization Table: Optimization of the Reaction Conditions .

Entry	Solvent	Visible Light	Yield (%)
1	Toluene	2 × 9 W Blue LEDs	21
2	Dichloromethane	2 × 9 W Blue LEDs	ND
3	Acetonitrile	2 × 9 W Blue LEDs	ND
4	MeOH	2 × 9 W Blue LEDs	75
5	EtOH	2 × 9 W Blue LEDs	82
6	H2O	2 × 9 W Blue LEDs	65
7	H2O/EtOH (1:1)	2 × 9 W Blue LEDs	85
8	H2O/EtOH (2:1)	2 × 9 W Blue LEDs	98
9	H2O/EtOH (2:1)	1 × 7 W Green LED	75
10	H2O/EtOH (2:1)	1 × 7 W White LED	57
11	H2O/EtOH (2:1)	1 × 10 W White LED	80
12	H2O/EtOH (2:1)	1 × 9 W Blue LED	94
13	H2O/EtOH (2:1)	1 × 9 W Red LED	49
14	H2O/EtOH (2:1)	1 × 7 W Yellow LED	62
15	H2O/EtOH (2:1)	Absence of Light	N.R.

^aReaction conditions: 1 (1.0 mmol), 2a (1.0 mmol), 3 (1.0 mmol), solvent (3 mL), rt, 120 min.

^bIsolated yield. N.R. = no reaction.

4.

Light on/off process of the reaction.

Eventually, the experiment was carried out with various light sources in a water/ethanol solvent mixture (2:1, v/v) to check the effect of the intensities of the light on the reaction. When the reaction was performed under the irradiation of one 9 W blue LED (Table , entry 12), the results were not better than when two 9 W blue LEDs were used, implicating the necessity of more photons. The white LED of 7 W (Table , entry 10) and the green LED (Table , entry 9) of 7 W did not have more influence on the reaction than the two blue LEDs of 9 W. Furthermore, irradiating the reaction mixture with a white LED (10 W) (Table , entry 11) did not improve the results. These observations suggest that sufficient photon density in the blue region of the visible spectrum is the reason for the efficiency of this reaction. This result led to the conclusion that two 9 W blue LEDs (Table , entry 8) are the optimal visible light source for this reaction.

Therefore, the optimal reaction condition is determined to be the use of an aqueous ethanolic medium in a 2:1 ratio with two 9 W blue LEDs. Keeping this ideal state in mind, several substrates were subsequently experimented with, especially amines and aldehydes with electron-donating and -withdrawing groups, to discover more about the reaction’s flexibility (Scheme ). In Scheme , the aldehyde, paraformaldehyde, remained constant while varying the amines. Initially, product 3aa was obtained with a yield of 98%. P-anisidine and o-anisidine with the -OMe group produced the respective compounds 3ab and 3ae in varying yields. The +R effect of -OMe at the para position enhances electron density on the –NH₂ of p-anisidine (3ab, >99%), but the –I effect obscures the +R at the ortho location, resulting in a decreased yield of product 3ae (84%). Similarly, o-, and m-aminobenzoic acids contribute to the production in much lower amounts of 3ad and 3am, requiring more time for formation than for the other aldehydes. The –COOH group’s electron-withdrawing property (–I effect) and the resonance effect make it harder for the amine group to form the EDA complex in the ortho position (3ad, 64%) in comparison to the meta position (3am, 71%). Aniline, as an unsubstituted aromatic amine, generated 3ah in good yield (90%). Despite having an –NH₂ electron-donating group, the pyridine ring in 2-aminopyridine (2n) is less electron-rich than aniline-type donors, and this is why its corresponding N-oxide (3an) gets formed after a long period of time. Halogen-substituted aromatic amines possessing electron-withdrawing halogen groups with the –I effect reduce the reactivity of the amines as an electron donor and provide their corresponding compounds in different yields, and they also require a comparatively longer time to participate in the reaction. As a result, o-bromoaniline and p-bromoaniline form the corresponding imidazole N-oxides in 75% (3ac) and 86% (3ag), respectively, whereas the +R effect of chlorine in o-chloroaniline and p-chloroaniline helps produce their corresponding N-oxides in 72% (3al) and 90% (3af), respectively. Aromatic amines with –Me, –NH₂ substituents have a greater electron density on the nitrogen, facilitating EDA complexes’ formation. In this regard, p-toluidine and o-phenylenediamine bring about the corresponding N-oxides (3ai, 85%, and 3aj, 91%) in moderate to good yields.

3. Scope of Amines (2a–n) with Diacetylmonoxime (1) and Paraformaldehyde (3) in the Photoinduced Synthesis of Imidazole N-Oxides (3aa–3an).

In the next scheme (Scheme ), different aromatic aldehydes were used while keeping the amine constant at benzylamine. Aromatic aldehydes containing electron-withdrawing groups produce a higher electrophilic character on the aldehydic carbon, making them favorable for the development of ternary EDA complexes. For example, m-nitrobenzaldehyde gives rise to 5e in 88%, whereas m-hydroxybenzaldehyde yields 5d in 80%. Conversely, o-hydroxybenzaldehyde, o-methoxybenzaldehyde, and o-tolualdehyde take part in the reaction to make the corresponding products (5c, 5g, and 5b) in low yield due to the reduction of the electrophilic nature at the aldehydic carbon center.

4. Scope of Aldehydes (4a–h) with Diacetylmonoxime (1) and Benzylamine (2a) in the Photoinduced Synthesis of Imidazole N-Oxides (5a–h).

The results from the previous strategies kept us so astounded that one additional approach (Scheme ) for the synthesis of imidazole N-oxide has been developed, utilizing diacetyl monoxime, several aldehydes (7a–p), and ammonium acetate (6) under optimal conditions. The electron-pushing nature of the electron-donating group makes carbonyl carbon less electron-deficient, and this effect is more pronounced in the case of the ortho-isomer than the para-isomers, resulting in the lower yield of the product for the former ones. For example, o-hydroxybenzaldehyde, o-tolualdehyde, and o-methoxybenzaldehyde undergo the reaction forming their respective products (8b, 68%; 8f, 72%; and 8d, 54%; respectively) in significantly lower yields than their para ones (8a, 71%; 8g, 76%; and 8c, 58%; respectively). Moreover, o-chlorobenzaldehyde (7p) is involved in the reaction to form the N-oxide (8p, 82%) in a higher yield than the ortho isomers of the electron-donating group-containing aldehydes (7b, 7d, and 7f) due to the higher reactivity of the former aldehyde. Furfural (7m) participates significantly in the synthesis of product 8m in a good yield of 84%. In a better yield, isophthalaldehyde (7l) and benzaldehyde (7n) are involved in the synthesis of their respective imidazole N-oxides (8l, 90%; and 8n, 91%; respectively).

5. Scope of Aldehydes (7a–p) with Diacetylmonoxime (1) and Ammonium Acetate (6) in the Photoinduced Synthesis of 1H-Imidazole N-Oxides (8a–p).

Unlike Scheme , the next scheme (Scheme ) proposes an equivalent method for synthesizing 1H-imidazole 3-oxide by utilizing hydroxylamine hydrochloride (9, NH₂OH HCl) instead of NH₄OAc. Along with the diacetyl monoxime and NH₂OH HCl, the reaction comprised a range of aromatic aldehydes with electron-donating and electron-withdrawing groups as well as paraformaldehyde.

6. Scope of Aldehydes (10a–l) with Diacetylmonoxime (1) and Hydroxylamine Hydrochloride (9) in the Photoinduced Synthesis of 1-Hydroxy-imidazole N-Oxides (11a–l).

So far, the use of diacetyl monoxime with amines and aldehydes has led to satisfactory outcomes. Now, the methyl groups in diacetyl monoxime were substituted with bulkier phenyl ones, leading to diphenylmonoxime (1″). Scheme demonstrates the synthesis of imidazole N-oxides using diphenylmonoxime (1″), amines, ammonium acetate, or hydroxylamine hydrochloride (12a, 12b, or 12c), and aldehydes (13a,b) under the irradiation of two blue LEDs (9 W) in a H₂O–EtOH mixture (2:1 v/v). It seems that this time, the product takes slightly longer to develop, most likely due to the bulkiness of the phenyl ring, which makes the EDA complex difficult to form.

7. Scope of Diphenylmonoxime (1″) with Aldehydes (13a,b) and Amines, Ammonium Acetate, or Hydroxylamine Hydrochloride (12a–c) in the Photoinduced Synthesis of Imidazole N-Oxides (14a–f).

2.1. Gram-Scale Synthesis of Imidazole N-Oxide (3aa, 1-Benzyl-4,5-dimethyl-1H-imidazole 3-Oxide)

In an oven-dried round-bottomed flask, a mixture of diacetyl monoxime (1, 10 mmol), benzylamine (2a, 10 mmol), and paraformaldehyde (3, 10 mmol) in aqueous ethanolic medium (H₂O/EtOH, 2:1, v/v) was stirred under irradiation of a blue LED (2 × 9W) at room temperature for 2 h. This time, 72% of the intended product was obtained (Scheme ). The scalability of the reaction was assessed by performing the transformation on the scale of 1 to 10 mmol (see the Supporting Information Figure S2).

8. Gram-Scale Synthesis of 1-Benzyl-4,5-dimethyl-1H-imidazole 3-Oxide.

Several control tests (Scheme a–g) have been conducted to further reinforce the reaction pathway and validate the requirement of the reaction. The significance of atmospheric O₂ was evident when a minimal quantity (5%) of the imidazole N-oxide product was generated in an argon environment (Scheme d). The involvement of light in the reaction was validated when the product yield was dropped drastically from 75% to 18% (Scheme c) by carrying out the reaction in the dark and in the presence of atmospheric O₂. Based on these observations, it is possible to conclude that light dependency supports a photochemical pathway and oxygen is required as a reactive species rather than an inert atmosphere. These results correspond with an oxygen-dependent photooxidation mechanism, which may include reactive oxygen species such as singlet oxygen (¹O₂) or radical intermediates (such as superoxides, O₂ ^•‑). The addition of AgNO₃ (Scheme f) inhibited product formation and resulted in the deposition of a metallic black mirror, implying the reduction of Ag­(I) to Ag(0). This finding suggests that a significant reduction in intermediates has been captured and confirms the single electron-transfer (SET) role in the reaction medium. The addition of NaN₃ (Scheme e) only partially inhibited product formation, suggesting the presence of short-lived radical intermediates because sodium azide acts as a singlet oxygen quencher, and its incomplete inhibition implies that the reaction does not follow a long-chain radical route but rather a photoinduced single-electron transfer (SET) process involving short-lived radical species. The addition of benzoquinone (Scheme g) results in a significant decrease in yield, highlighting the importance of superoxide radical species (O₂ ^•‑) in this reaction pathway.

9. Some Control Experiments (a–g).

A radical trapping experiment (Scheme ) including 2, 2, 6, 6-tetramethylpiperidin-1-oxyl (TEMPO) in the H₂O/EtOH (2:1) solvent mixture of diacetyl monoxime (1), benzylamine (2a), and p-hydroxybenzaldehyde (4f) was performed to represent a justifiable mechanistic pathway. This radical reaction route gave a noticeable indication by preventing the formation of the product, 5f. Additionally, the recognition of a TEMPO-p-hydroxybenzaldehyde adduct (X) and a TEMPO-benzylamine (Y) adduct by LC–MS analysis of the reaction fraction remarkably validates the radical pathway of the reaction. Along with this, High-Performance Liquid Chromatography (HPLC) of the reaction mixture (Scheme ) was performed (see Supporting Information, Figure S9) to quantify the extent of conversion of the radical-trapped adducts and to evaluate the efficiency of the radical trapping process by TEMPO. HPLC analysis revealed that there is 56% and 8% conversion to the radical-trapped adducts.

10. Reaction of TEMPO with Diacetylmonoxime (1), Benzylamine (2a), and p-Hydroxybenzaldehyde (4f) in the Presence of Visible Light.

When the reactants [diacetylmonoxime (1), benzylamine (2a), and p-hydroxybenzaldehyde (4f)] were mixed altogether in the aqueous ethanolic medium (H₂O/EtOH, 2:1, v/v), a brownish color appeared (Figure ) as an initial sign of the formation of an electron-donor–electron-acceptor complex in the mixture. Analysis of the individual reactants under UV–vis spectroscopy (Figure ) did not provide any noticeable absorption in the visible region. Subsequently, the absorption of binary mixtures (1 + 2a, 2a + 4f, and 1 + 4f) was examined using UV–vis spectroscopy. Interestingly, a slight bathochromic shift occurred in the combination of 2a + 4f. Furthermore, a more pronounced bathochromic shift was observed in the ternary mixture (1 + 2a + 4f) compared to their individual and binary mixture. This bathochromic shift proposed the formation of an EDA complex where p-hydroxybenzaldehyde (4f) and diacetyl monoxime (1) function as the acceptor and benzylamine (2a) functions as the donor.

2.

UV–visible spectroscopy of the reactants, binary mixtures, and the ternary mixture [RM 1 (=Reaction Mixture 1) and RM 2 (=Reaction Mixture 2) are the ternary mixture of the reacting components in high concentration].

To provide concrete evidence on the development of the EDA complex between 1, 2a, and 4f, the Job’s plot experiment was performed, revealing the 1:1 complexation between 1 + 4f and 2a (Figure a). Afterward, to further verify the formation of the ternary EDA complex, the association constant (K _a) was calculated by using the modified Benesi–Hildebrand equation, and it was found to be 1.1975 × 10⁶ M^–1 (Figure b).

3.

(a) Job’s Plot of the EDA complex in aqueous ethanol (1:1 stoichiometric ratio of 1a + 4f and 2a). (b) Calculation of K _a using the Benesi–Hildebrand equation.

Then, the concept of the electron transfer mechanism was strongly established with the help of a cyclic voltammetry (CV) experiment of the individual components (see Supporting Information, Figure S6). It is initially assumed that the amine (2a) reacts with compound 1 through an electron transfer from the lone pair of nitrogen of amine (2a) to the π* antibonding orbital of the α-imino carbonyl moiety in 1. This process suggests an overview that the amine is being oxidized, while compound 1 is being reduced. Experimentally, it has also been proved that the amine (2a) is oxidized at +1.4 V and compound 1 is reduced at −1.0 V. The possibility of the reaction between the amine and aldehyde 4f has been excluded due to the lower reduction potential of 4f (−1.2 V) in comparison to 1, implying that compound 1 is more electronically deficient than 4f (see Supporting Information, Figure S7). As soon as the carbonyl functional group of compound 1 gets transformed into an imine, leading to di-imine species IV (see mechanism) via the electron transfer reaction with the amine (2a), followed by tautomerisation to form V, then V subsequently reacts with aldehyde 4f through a similar electron transfer process. The reduction potential of compound 4f is about −1.2 V, and species V is rich in π-electrons, indicating a strong tendency for electron transfer from V to 4f. A light-on/-off control experiment was conducted to determine the essential role of visible light irradiation in the reaction. A mixture of diacetyl monoxime (1), benzylamine (2a), and paraformaldehyde (3) in an aqueous ethanolic medium (H₂O/EtOH, 2:1, v/v) was stirred periodically at room temperature for 180 min with 30 min intervals under the irradiation of blue LEDs (2 × 9 W). The yield of the product at every interval has been depicted in the following figure (Figure ). Product production was noticed only throughout the period of irradiation, and no additional conversion happened when the light source was turned off. The observation indicates that the synthesis is actually photodriven, ruling out the concept of a purely thermal mechanism.

2.2. Mechanism

In light of the experimental results, CV experimental outcomes are compared with the redox potentials (Figure S7), radical trapping experiments, and supporting literature, and a plausible mechanistic pathway is suggested (Figure ). At the start, radical pairs I and II (discovered by LC-MS for the radical trapping experiment) form when the ground-state EDA complex is stimulated to the excited-state EDA complex, which is followed by proton-coupled electron transfer (PCET). Then, radical–radical coupling between the radical pairs (I and II) allows them to form III, which then eliminates a water molecule to produce IV. Tautomerization of IV and PCET with 4f helps generate VI. Consequently, radical–radical coupling again gives VII. Afterward, the lone pair of nitrogens attacks at the electrophilic center, followed by aromatization, to generate our desired product, 5f.

5.

Plausible mechanism for the formation of imidazole N-oxide by photoexcitation.

The green chemistry profile of the visible-light-mediated developed one-pot synthesis technique was thoroughly evaluated using a comprehensive green metrics analysis. , All synthesized compounds under Schemes – were evaluated for parameters such as effective mass yield (EMY), atom economy (AE), atom efficiency (AEf), reaction mass efficiency (RME), optimum efficiency (OE), mass productivity (MP), mass intensity (MI), process mass intensity (PMI), E-factor, and solvent and water intensities (SI and WI) (see Supporting Information Tables S8 and S9). The estimated effective mass yield, atom economy, and atom efficiency for this procedure are up to 87.57%, 90.48%, and 87.76%, respectively. The most effective statistics for assessing the greenness of a process are atom economy and reaction mass efficiency (RME), which account for all reactant mass and yield. The majority of the synthesized derivatives had reaction mass efficiency (RME) values ranging from 41 to 87.57%, indicating that reactant mass was efficiently incorporated into the desired products. Only eight compounds have considerably lower RME values (∼30–38%). Despite these cases, the general RME distribution demonstrates high material efficiency and adds credibility to the green qualities of the process. The process mass intensity (PMI) evaluation (56.34–19.88 g/g) supports this finding. The estimated E-factor values ranged from 0.14 to 2.31. Most of the synthetic derivatives had E-factors near or less than one, indicating negligible waste formation under the optimal conditions. Even the highest measured value (2.31) falls within the permitted range for laboratory-scale fine chemical synthesis. Overall, the low E-factor results significantly support the waste minimization and environmental friendliness of this procedure. All of the respective formulas, data, and calculations are provided in the Supporting Information file.

3. Crystallization Method

3.1. Data Collection and Instrument Specification

We measured the diffraction from the single crystal using a Bruker D8 Quest machine with 50 kV and Mo Kα (λ = 0.71073 Å) radiation. We reduced the final data sets by using the APEX3 program. For further analysis, we applied the full-matrix least-squares on F2 method (SHELXL-2016 55), part of the WinGx suite of programs (Version 1.63.04a). The structure determination has been firmly established by the single crystal X-ray diffraction (SC-XRD) of the compound, 2-(furan-2-yl)-4,5-dimethyl-1H-imidazole 3-oxide (8m) (Figures and ). The single crystal was formed by the slow evaporation of a water/ethanol mixture of compound 8m. We fixed all the hydrogen atoms, except for the water molecule and N–H, at calculated positions and included them in the refinement process using a riding model with isotropic thermal parameters. The compound crystallizes into a monoclinic crystal structure bearing space group P2₁/n. The mentioned single crystals have the unit cell dimensions as follows: a = 8.5549(5) Å, b = 8.0969(4) Å, c = 14.9737(8) Å, α = 90°, β = 104.631(2)°, ϒ = 90°, Z = 4, μ = 0.085 mm^–1, F(000) = 376, and calculated density = 1.179 mg/m³.

6.

Unit cell of the crystallographic structure of 2-(furan-2-yl)-4,5-dimethyl-1H-imidazole 3-oxide (8m).

7.

Standard ball–stick model of the crystallographic structure of 2-(furan-2-yl)-4,5-dimethyl-1H-imidazole 3-oxide (8m). The oxygen atom of the water molecule is not shown.

3.2. Theoretical Insights into the MechanismDFT Calculations

The geometries of all systems (1, 2a, 4f, 1 + 2a, 2a + 4f, and 1 + 2a + 4f) were optimized using density functional theory (DFT) with the B3LYP functional and Grimme’s D3BJ dispersion correction used for binary and ternary mixtures, employing the 6-311++G­(d,p) basis set in the gas phase, as implemented in the ORCA 6.0 program package. Time-Dependent Density Functional Theory (TD-DFT) calculations were performed using the same functional and basis set in a H₂O/EtOH (2:1) solvent medium (dielectric constant ε = 60.4) for the individual molecules as well as the binary systems (1 + 2a), (1 + 4f), and (2a + 4f) and the ternary complex (1 + 2a + 4f) in order to reproduce the UV–visible absorption spectra. In the TD-DFT calculations, 20 excited states were considered (see Sections 4.1–4.7 in the Supporting Information). The theoretical results indicate that individual molecules and the binary mixture (1 + 2a) have no appreciable absorption band in the visible region. But, in contrast, the binary mixture (2a + 4f) displayed noticeable absorption in the visible region, and (1 + 4f), (1 + 2a + 4f) show an absorption band in the visible region. All of the results can be elucidated using the TD-DFT-based UV–visible spectra in Figure . The theoretical findings support the probable formation of both binary and ternary complexes during the reaction process.

8.

TD-DFT-based UV–vis spectra.

From the optimized geometries, it was found that the difference between the HOMO of compound 2a and the LUMO of compound 1 is 4.234 eV, and the difference between the HOMO of compound 2a and the LUMO of compound 4f is 4.44 eV. So, the possible electron transfer is likely taking place from the HOMO of 2a to the LUMO of 1, or electron transfer from the HOMO of 2a to the LUMO of 4f. The molecular orbital diagrams corresponding to the HOMO and LUMO of 1, 2a, and 4f are shown in the following figure (Figure ).

9.

Orbital diagrams of 1/HOMO and 1/LUMO, 2a/HOMO and 2a/LUMO, and 4f/HOMO and 4f/LUMO.

3.3. Biological Evaluation

3.3.1. In Vitro Biological Activities

The synthesized compounds were systematically evaluated through antioxidant, antidiabetic, and anti-inflammatory assays, as illustrated in Chart . The biological evaluation was conducted on 56 samples that exhibited measurable activity across the tested assays.

1. Antioxidant Activities Assessed Using the (A) DPPH, (B) ABTS, and (C) FRAP Assays, along with (D) Anti-diabetic and (E) Anti-inflammatory Activities of the Samples; Data Are Represented as Mean ± SD (Replicate Number, n = 3).

3.3.2. Antioxidant Potential

The DPPH radical scavenging method was used to evaluate the antioxidant activity, which operates on the principle that antioxidant molecules can donate electrons or hydrogen atoms to stabilize the DPPH radical, leading to a measurable reduction in absorbance at 517 nm. This decline reflects the ability of the compound to neutralize free radicals, with lower IC₅₀ values indicating higher efficacy. − Chart A–C shows the antioxidant potential using the DPPH, ABTS, and FRAP assays. The standards showed IC₅₀ values of 18.12 μg/mL for DPPH, 185.36 μg/mL for ABTS, and 190.57 μg/mL for FRAP. The samples containing hydroxyl, methoxy, or methyl groups consistently exhibited stronger radical-scavenging and reducing power as electron-donating substituents stabilize radicals and enhance electron transfer. , Several compounds, including 3ac, 5a, 8b, 8g, 8m, 11e, 11h, 11k, and 14d, exhibited activity stronger than that of the standard, with IC₅₀ values ranging from 5.15 to 12.98 μg/mL (DPPH), 52.59 to 166.29 μg/mL (ABTS), and 76.67 to 126.02 μg/mL (FRAP). Compounds 8c and 8i also showed notable inhibition with values close to their standards. In contrast, compounds such as 3ab, 8o, 8p, 11a, 14a, and 14f showed significantly higher IC₅₀ values, indicating weak antioxidant capacity.

3.3.3. Antidiabetic Activity

In parallel, the antidiabetic activity was determined via α-amylase inhibition, with IC₅₀ values reflecting the extent of enzyme suppression, as shown in Chart . Given publications relating intercellular adhesion molecule-1 (ICAM-1) genetic variations and altered selenoprotein regulation with diabetes history, the synthesized compounds were initially evaluated for antidiabetic activity with acarbose as the reference standard. Acarbose, used as the standard, yielded an IC₅₀ of 37.81 μg/mL. The antidiabetic activity of the samples (Chart D) showed that hydrophobic and aromatic substitutions, such as methyl and phenyl, improved α-amylase inhibition and glucose uptake compared to the standard (37.81 μg/mL). This finding aligns with earlier research on quinoline-imidazole hybrids. Several synthesized compounds, notably 3ad, 3ae, 3ah, 3ai, 3ak, 3al, 3an, 5b, 5c, 5e, 5f, 5g, 5h, 8d, and 8h, demonstrated stronger inhibitory effects, with IC₅₀ values ranging from 26.06 to 34.55 μg/mL. Additional promising results were observed for 5d, 8b, 11b, 11e, 11i, 14a, 14d, and 14e, which fell within the 44.10–99.45 μg/mL range. The least effective activity was shown by 3ab, 8f, 8j, 8k, 8l, 8o, and 8n, with IC₅₀ values between 368.30 and 969.01 μg/mL. The samples such as 8c, 8e, 11d, 11j, and 14c did not show this activity. These outcomes suggest that a specific structure shows the α-amylase inhibition, contributing to the antidiabetic potential of selected compounds.

3.3.4. Anti-inflammatory Activity

The anti-inflammatory activity, illustrated in Chart , was evaluated by inhibiting protein denaturation, a process linked to inflammatory responses. Diclofenac sodium was the reference, with an IC₅₀ of 96.34 μg/mL. Chart E illustrates the anti-inflammatory activity of the samples, which followed a similar structural pattern. Lipophilic substituents, such as phenyl, methoxy, and methyl, increased receptor binding and potency, while acidic groups, such as carboxyl, contributed to moderate COX inhibition. However, halogenated and nitro derivatives reduced hydrogen bonding and reduced the activity compared to the standard (96.34 μg/mL). Our results confirm that electron-donating and lipophilic groups consistently improve activity across antioxidant, antidiabetic, and anti-inflammatory assays, while strong electron-withdrawing substituents compromise it, reinforcing the therapeutic potential of rationally designed derivatives. Several compounds, including 3ac, 3ad, 3ae, 3ag, 3ai, 3al, 5a, 5b, 8e, 8i, 8m, 8p, 11b, 11c, 11k, 11l, 14b, 14c, and 14d, exhibited stronger activity than the standard, with IC₅₀ values ranging from 50.1 to 61.75 μg/mL. Compounds 3aa, 3ak, 5c, 5f, 8d, 8f, 8l, 11g, and 14f also showed notable inhibition, with values ranging from 92.95 to 195.08 μg/mL. Furthermore, compounds such as 3ah, 3am, 5e, 5g, 5h, 8h, 8k, 8n, and 11a displayed higher IC₅₀ values (227.70–475.93 μg/mL), indicating low anti-inflammatory potential. Several samples, including 3af, 5d, 8a, 8b, 8c, 8j, 11d, 11h, 11i, 11j, 14a, and 14e, did not show activity in this assay. These findings suggest that molecular features influencing protein stabilization may play a role in the anti-inflammatory efficacy of these compounds.

3.3.5. In Vitro Analysis

After analyzing the antioxidant, antidiabetic, and anti-inflammatory activities of the 56 synthesized compounds, they were subjected to an in vitro cytotoxicity assay to evaluate their safety profiles. The cytotoxicity activity of the compounds was conducted in the WRL-68 cell line , to determine their toxicity in normal hepatic cells.

3.3.6. Cytotoxicity

The chemical assays (antioxidant, antidiabetic, and anti-inflammatory activities) can be correlated with cytotoxicity in the WRL-68 normal human liver cell line by measuring therapeutic selectivity. It can be said that a compound exhibiting significant chemical assays with low cytotoxicity toward WRL-68 cells indicates a favorable safety level, while considerable cytotoxicity at or near bioactive concentrations suggests restricted therapeutic potential due to inadequate selectivity.

While the products of Scheme are analyzed for cytotoxicity assessment in the WRL-68 cell line (Chart ), it can be observed that for the products 3aa, 3af, 3ah, 3ai, 3aj, and 3am, cell viability remained above 50% even up to 250 μg/mL of concentration, which indicates that the cytotoxic IC₅₀ value was not reached within the experimental range. Considering their chemical assays (Chart ) and these findings, it can be stated that despite having weak antioxidant and antidiabetic activities, they exhibit low cytotoxicity in normal hepatic cells. Compound 3ac, showing effective antioxidant activity (5.16 μg/mL) and anti-inflammatory activity (52.35 μg/mL), possesses a low to moderate IC₅₀ value in the WRL-68 cell line. Compound 3ag exhibits good anti-inflammatory activity (54.14 μg/mL) with a moderate IC₅₀ value (Table ) in the WRL-68 cell line.

2. Cytotoxicity of Compounds (Scheme ) against the WRL-68 Cell Line.

2. Compounds with Their Respective IC₅₀ Values.

Compounds	IC50 ± SD (μg/mL)
3aa	ND
3ab	162.48 ± 8.28
3ac	177.69 ± 5.98
3ad	119.31 ± 10.13
3ae	237.1 ± 4.81
3af	ND
3ag	143.87 ± 5.35
3ah	ND
3ai	ND
3aj	ND
3ak	157.89 ± 5.81
3al	81.3 ± 5.52
3am	ND
3an	200.2 ± 8.23

Cytotoxicity of compounds of Scheme against the WRL-68 cell line is illustrated with their respective IC₅₀ values in Chart and Table . Compound 5h exhibits the best cell viability in the WRL-68 cell line among all of the compounds in Scheme . Compound 5a, which shows good antioxidant and anti-inflammatory activity, exhibits low cytotoxicity at higher concentrations (250 μg/mL) in the WRL-68 cell line.

3. Cytotoxicity of Compounds (Scheme ) against the WRL-68 Cell Line.

3. Compounds with Their Respective IC₅₀ Values.

Compounds	IC50 ± SD (μg/mL)
5a	ND
5b	200.39 ± 5.25
5c	126.58 ± 8.29
5d	232.94 ± 6.34
5e	ND
5f	244.95 ± 5.58
5g	225.33 ± 5.17
5h	ND

The compounds of Scheme were tested for cytotoxicity against the WRL-68 cell line, and they gave very significant results (Chart ). Several compounds from this scheme show cell viability of more than 50% even at a higher concentration (250 μg/mL). For this reason, their IC₅₀ values could not be determined in their experimental range (Table ). Compounds 8a, 8f, and 8k exhibit the lowest cytotoxicity in the WRL-68 cell line. Compounds 8i, 8m, and 8p, which show promising anti-inflammatory activity, possess low toxicity in the WRL-68 cell line, which makes them safe for use in normal cells. Compound 8m has good antioxidant activity and high IC₅₀ values in the WRL-68 cell line, proposing a desirable balance between bioactivity and cellular safety.

4. Cytotoxicity of Compounds (Scheme ) against the WRL-68 Cell Line.

4. Compounds with Their Respective IC₅₀ Values.

Compounds	IC50 ± SD (μg/mL)
8a	ND
8b	156.22 ± 5.58
8c	152.21 ± 8.32
8d	178.62 ± 6.66
8e	221.47 ± 8.19
8f	ND
8g	ND
8h	ND
8i	ND
8j	180.08 ± 9.66
8k	ND
8L	ND
8m	ND
8n	ND
8o	ND
8p	ND

The compounds formed according to Scheme were tested for their cytotoxicity in the WRL-68 cell line, and the corresponding results are presented in Chart and Table . Compounds 11a and 11k exhibit the lowest cytotoxicity within the experimental concentration range, suggesting that they are safe for use in normal cells. Compound 11k also showed strong antioxidant and anti-inflammatory properties, and its low cytotoxicity toward WRL-68 cells suggests potential safety for future biological uses. Compounds 11e and 11h, having significant antioxidant properties, shows very high IC₅₀ values (could not be determined for 11e in the experimental range and 232.02 μg/mL for 11h, even at the higher concentration).

5. Cytotoxicity of Compounds (Scheme ) against the WRL-68 Cell Line.

5. Compounds with Their Respective IC₅₀ Values.

Compounds	IC50 ± SD (μg/mL)
11a	ND
11b	210.25 ± 4.22
11c	184.38 ± 7.08
11d	159.74 ± 5.78
11e	ND
11f	174.57 ± 9.55
11g	243.66 ± 7.14
11h	232.07 ± 7.26
11i	214.95 ± 7.86
11j	215.06 ± 10.43
11k	ND
11l	ND

The compounds synthesized from Scheme were evaluated for their cytotoxicity in the WRl-68 cell line, and the results are presented in Chart and Table . Among them, compound 14f exhibited the lowest cytotoxicity, which indicates low risk in comparison to the other compounds in this scheme toward normal liver cells within the experimental concentration range and suggests its suitability for further pharmacological evaluation.

6. Cytotoxicity of Compounds (Scheme ) against the WRL-68 Cell Line.

6. Compounds with Their Respective IC₅₀ Values.

Compounds	IC50 ± SD (μg/mL)
14a	157.21 ± 10.23
14b	51.89 ± 6.71
14c	116.28 ± 11.98
14d	129.67 ± 8.64
14e	106.85 ± 7.82
14f	ND

4. Conclusion

In conclusion, a visible-light-mediated strategy for the synthesis of imidazole N-oxide derivatives has been established in an aqueous ethanol medium by forming an electron donor–acceptor (EDA) complex under mild and environmentally friendly conditions. The UV–visible spectroscopy of 1, 2a, and 4f revealed an identifiable absorbance at around 410 nm, confirming the donor–acceptor interaction. Both the cyclic voltammetry (CV) experiment and the theoretical investigation of the energy gap of the HOMO and LUMO of the reactants demonstrated that 2a functions as the reducing agent, whereas 1 and 4f act as the oxidizing agents, indicating the feasibility of photoinduced electron transfer. The stoichiometry of the reactants in the EDA complex was determined by the Job’s plot, which confirmed 1:1 complexation between 1 + 4f and 2a. The binding constant (K _a) was assessed by the modified Benesi–Hildebrand equation and found to be 1.1975 × 10⁶ M^–1. Control experiments and TEMPO-based radical trapping experiments provided a more mechanistic understanding. The formation of TEMPO-2a and TEMPO-4f adducts was verified by LC-MS analysis, and HPLC investigations revealed 56% and 8% conversion, respectively, indicating a radical-mediated route. The practical application of this procedure was established by gram-scale synthesis, which produced the target product in 72% yield, while scale-up experiments detected the difference in yield from the mmol to higher mmol scales. Furthermore, theoretical investigations utilizing TD-DFT calculations confirmed the development and electronic properties of the EDA complex, which were consistent with the experimental findings. The sustainability of this method was further highlighted by an evaluation of the green chemistry parameters (EMY, AE, AEf, PMI, E-factor, RME, OE, MP, MI, SI, and WI). The atom economy (AE) values, ranging from 47.58% to 90.48%, represent moderate to high theoretical efficiency, indicating that reactant atoms are effectively incorporated into the expected product. The process mass intensity (PMI) values for the 56 synthesized compounds varied from 19.88 to 56.34 g/g, and the E-factor for most of the compounds was near or less than one, suggesting minimal waste formation and increased environmental friendliness. The optimal efficiency (OE) values (54.11–99.53%) indicate moderate to near-quantitative practical material utilization, highlighting operational efficiency and synthetic feasibility. In summary, this work describes a mechanistically supported, scalable, and sustainable visible-light-driven strategy for the synthesis of imidazole N-oxide derivatives. After testing for antioxidant, antidiabetic, and anti-inflammatory properties, some of the 56 imidazole N-oxide derivatives showed interesting bioactivity. Compounds 3ac, 5a, 8b, 8g, 8m, 11e, 11h, 11k, and 14d showed high antioxidant potential (DPPH: IC₅₀ = 5.15–12.98 μg/mL; ABTS: IC₅₀ = 52.59–166.29 μg/mL; FRAP: IC₅₀ = 76.67–126.02 μg/mL), while compounds 3ad, 3ae, 3ah, 3ai, 3ak, 3al, 3an, 5b, 5c, 5e, 5f, 5g, 5h, 8d, and 8h showed strong antidiabetic activity (IC₅₀ = 26.06–34.55 μg/mL). Compounds 3ac, 3ad, 3ae, 3ag, 3ai, 3al, 5a, 5b, 8e, 8i, 8m, 8p, 11b, 11c, 11k, 11l, 14b, 14c, and 14d showed significant anti-inflammatory activities (IC₅₀ = 50.1–61.75 μg/mL), indicating that these scaffolds are desirable, versatile synthesized compounds for future studies and research.

5. Experimental Details

5.1. General Procedure for the Synthesis of Products (Schemes –)

In an oven-dried round-bottomed flask, a mixture of diacetyl monoxime (1 mmol, for Schemes –) or diphenylmonoxime (1 mmol, for Scheme ), aromatic amine (1 mmol, for Schemes and ) or benzylamine (1 mmol, for Schemes , , and ) or ammonium acetate (2 equiv, for Schemes and ), or hydroxylamine hydrochloride (NH₂OH HCl) (2 equiv, for Schemes and ), and paraformaldehyde (1 mmol, for Schemes , and ) or aromatic aldehyde (1 mmol, for Schemes –) in aqueous ethanolic medium (H₂O/EtOH, 2:1, v/v) was stirred under irradiation from a blue LED (2 × 9W) at room temperature for 2 h. The formation and completion of the imidazole N-oxide was observed by thin-layer chromatography (TLC). Afterward, the reaction mixture was dried and washed with diethyl ether and ethyl acetate to obtain the product. The formation of imidazole N-oxide was confirmed by ¹H, ¹³C NMR spectroscopy and mass spectrometry.

5.2. In Vitro Biological Activities

5.2.1. DPPH Radical Scavenging Assay

A stock solution (2 mg/2 mL) of each sample and the standard (ascorbic acid) was prepared in methanol, followed by serial dilutions ranging from 10 to 100 μg/mL. In an Eppendorf tube, 1 mL of each dilution was combined with 1 mL of a 0.3 mM DPPH solution and kept in the dark at room temperature for 30 min. Using methanol as a blank, the absorbance was measured at 517 nm.

5.2.2. ABTS [2, 2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic Acid)] Radical Cation Scavenging Activity

ABTS solution was mixed with potassium persulfate and then incubated in the dark at room temperature to form ABTS^+•. A 2 ml ABTS solution (in MeOH) was mixed with the sample (1 mL). Further, the mixture was incubated at room temperature for 30 min, followed by measuring the absorbance at 734 nm. The IC₅₀ value was calculated and represented.

5.2.3. Ferric Reducing Power (FRAP) Assay

Sodium phosphate buffer (pH 6.6, 0.2 M, 2.5 mL) and potassium ferricyanide (1%), 2.5 mL were added to different concentrations of the samples. After incubation at 50 °C for 20 min, trichloroacetic acid (TCA) was added to the mixture, followed by centrifugation at 100 rpm for 10 min. Distilled water (25 mL) and 0.5 mL of ferric chloride (0.1%) were added to the upper layer. After vortexing, the absorbance was measured at 700 nm. Values were represented after calculating IC₅₀.

5.2.4. α-Amylase Inhibition Assay

Samples and the standard (acarbose) were prepared in phosphate buffer (0.02 M, pH 6.9) at 10 to 1000 μg/mL concentrations. Each test tube received 500 μL of the sample, followed by 500 μL of α-amylase solution (13 U/mL), and was incubated at 37 °C for 20 min. Subsequently, 500 μL of 1% starch solution was mixed, followed by incubation at 37 °C for 10 min. DNSA (1 mL) was used to stop the reaction. Absorbance was measured at 500 nm.

5.2.5. Egg Denaturation Assay

The anti-inflammatory activity was investigated using the egg albumin denaturation method. A mixture containing 0.2 mL of fresh egg albumin, 2 mL of samples (100–500 μg/mL), and 2.8 mL of phosphate-buffered saline (PBS, pH 6.4) was prepared. After incubation at 37 °C in a BOD incubator for 15–20 min, the samples were heated in a water bath at 70 °C for 8–10 min. Then, a 5 min cooling period at room temperature was observed, and absorbance was recorded at 660 nm using a UV–vis spectrophotometer.

5.3. In Vitro Assay

5.3.1. Cell Culture

The human normal fetal hepatic (WRL-68) cell line was cultured in DMEM high-glucose medium in 100 mm cell culture plates at 37 °C, 5% CO₂ conditions. The medium was supplemented with 10% FCS (Foetal Calf Serum), 100 units/mL penicillin, 100 μg/mL streptomycin, and 3.7 g/L sodium bicarbonate.

5.3.2. Cytotoxicity Study (MTT Assay)

After trypsinization, approximately 100 μL of the medium containing cells was seeded at a density of 5 × 10³ cells each well into a 96-well microtiter plate and kept overnight in a 37 °C, 5% CO₂ incubator for attachment. The next day, different concentrations (50, 100, 150, 200, and 250 μg/mL) of 3a, 5, 8, 11, and 14 series of samples dissolved in DMSO were added in a triplicate manner and kept again for 24 h incubation in a 37 °C, 5% CO₂ incubator. After 24 h, 10 μL of freshly prepared MTT dye solution [stock solution 5 mg/mL, dissolved in 1× PBS] was added to each well by removing the medium and kept again for another 3 h of incubation under the same conditions. Following incubation, 50 μL isopropanol was added to each well to solubilize the purple formazan crystals, and the plate was gently shaken for a few minutes. An OD was observed at 620 nm by the BMG Spectro Star Nano Spectrophotometer.

6. Characterization of Products

6.1. 1-Benzyl-4,5-dimethyl-1H-imidazole 3-Oxide (3aa)

White; yield 98%, 198.11 mg; ¹H NMR (400 MHz, CDCl₃): δ 7.69 (s, 1H); δ 7.01–6.97 (m, 3H); δ 6.76 (d, 2H); δ 4.70 (s, 2H); δ 1.83 (s, 3H); δ 1.73 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 134.36, 128.525, 127.795, 126.40, 126.27, 124.27, 120.76, 48.71, 8.25, 6.77. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 203.1184; found, 203.1120.

6.2. 1-(4-Methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3ab)

White; yield >99%, 217 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.395 (s, 1H), δ 7.373 (d, 2H), δ 7.065 (d, 2H), δ 3.800 (s, 3H), δ 2.05 (s, 3H); δ 2.03 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 159.22, 128.67, 127.90, 127.29, 125.82, 124.30, 121.37, 114.73, 9.10, 7.17. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 219.1134; found, 219.1078.

6.3. 1-(2-Bromophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3ac)

Cream white colored; yield 75%, 200.34 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.42 (s, 1H); δ 7.865 (d, 1H); δ 7.625 (d, 1H); δ 7.60–7.48 (m, 2H); δ 2.06 (s, 3H); δ 1.89 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 134.08, 133.50, 131.87, 130.56, 129.21, 125.78, 124.47, 121.93, 121.78, 8.72, 7.19. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 267.0133; found, 267.0119.

6.4. 1-(2-Carboxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3ad)

Light ivory colored; yield 64%, 148.63 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.92 (s, 1H); δ 7.98 (d, 1H); δ 7.85–7.77 (m, 1H); δ 7.73–7.63 (m, 1H); δ 7.07 (d, 1H); δ 2.08 (s, 3H); δ 1.91 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 166.72, 148.43, 133.31, 131.90, 130.97, 130.62, 129.82, 128.31, 123.63, 123.27, 8.10, 6.15. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 233.0926; found, 233.0856.

6.5. 1-(2-Methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3ae)

Cream white; yield 84%, 183.33 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 7.819 (s, 1H); δ 7.462 (dd, 1H); δ 7.168 (d, 1H); δ 7.036 (dd, 1H); δ 7.006 (d, 1H); δ 3.792 (s, 3H); δ 2.242 (s, 3H); δ 1.950 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 154.675, 131.153, 128.585, 126.427, 125.107, 123.440, 122.757, 120.939, 112.241, 55.721, 9.000, 7.419. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 219.1134; found, 219.1042.

6.6. 1-(4-Chlorophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3af)

White colored; yield 90%, 200.40 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 9.979 (s, 1H); δ 7.501 (d, 2H); δ 7.320 (d, 2H); δ 1.927 (s, 3H); δ 1.812 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 152.918, 134.984, 131.569, 129.303, 129.264, 113.367, 31.146, 9.565, 9.549. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 223.0638; found, 223.0639.

6.7. 1-(4-Bromophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3ag)

Light brownish colored; yield 86%, 229.72 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.520 (s, 1H); δ 7.735 (d, 2H); δ 7.445 (d, 2H); δ 2.09 (s, 3H); δ 2.05 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 134.83, 133.02, 128.23, 126.94, 124.49, 121.96, 121.61, 9.67, 7.57. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 267.0133; found, 267.0064.

6.8. 4,5-Dimethyl-1-phenyl-1H-imidazole 3-Oxide (3ah)

Amber colored; yield 90%, 169.40 mg; ¹H NMR (300 MHz, CDCl₃): δ 7.77 (s, 1H); δ 7.37–7.06 (m, 5H); δ 2.07 (s, 3H); δ 1.93 (s, 3H); ¹³C NMR (75 MHz, CDCl₃): 134.73, 129.69, 128.99, 127.23, 125.55, 124.06, 121.42, 9.28, 7.16. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 189.1028; found, 189.0933.

6.9. 4,5-Dimethyl-1-(p-tolyl)-1H-imidazole 3-Oxide (3ai)

Off white colored; yield 85%, 171.91 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 7.85 (s, 1H); δ 7.26–7.99 (m, 4H); δ 2.32 (s, 3H); δ 2.14 (s, 3H), δ 1.98 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 139.42, 132.19, 130.33, 127.02, 125.58, 124.45, 121.73, 21.03, 9.29, 7.27. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 203.1184; found, 203.1044.

6.10. 1-(2-Aminophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3aj)

Brown colored; yield 91%, 184.95 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 8.19 (s, 1H); δ 7.16 (dd, 1H); δ 6.99 (d, 1H); δ 6.77 (d, 1H); δ 6.59 (dd, 1H); δ 5.26 (s, 2H); δ 2.04 (s, 3H); δ 1.90 (s, 3H); ¹³C NMR (75 MHz, DMSO-d ₆): 145.35, 130.18, 128.74, 125.39, 124.22, 121.92, 119.32, 115.85, 115.81, 8.51, 7.35. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 204.1137; found, 204.1078.

6.11. 1-(3-Chlorophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3ak)

Light yellow colored; yield 74%, 164.77 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.55 (s, 1H); δ 7.65 (q, 1H); δ 7.61–7.46 (m, 3H); δ 2.11 (s, 3H); δ 2.07 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 136.69, 134.28, 131.73, 129.12, 126.87, 126.14, 125.02, 124.84, 121.76, 9.68, 7.58. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 223.0638; found, 223.0613.

6.12. 1-(2-Chlorophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3al)

Off white colored, yield 72%, 160.32 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.92 (s, 1H); δ 7.52 (d, 1H); δ 7.46–7.41 (m, 2H); δ 7.20 (dd, 1H); δ 2.91 (s, 3H); δ 2.42 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 143.29, 132.85, 131.09, 130.15, 129.26, 127.62, 126.87, 125.10, 120.83, 9.78, 7.26. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 223.0638; found, 223.0594.

6.13. 1-(3-Carboxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (3am)

Light bronze colored, yield 72%, 167.21 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 12.74 (s, 1H); δ 9.02 (s, 1H); δ 8.15 (s, 1H); δ 8.15–8.05 (m, 2H); δ 7.72 (s, 1H); δ 7.69 (s, 1H); δ 2.23 (s, 3H); δ 2.20 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 166.78, 141.98, 138.18, 135.29, 131.25, 129.86, 129.58, 127.36, 124.94, 108.14, 7.58. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 233.0926; found, 233.0852.

6.14. 4,5-Dimethyl-1-(pyridin-2-yl)-1H-imidazole 3-Oxide (3an)

Brown colored liquid, yield 82%; 155.16 mg; ¹H NMR (400 MHz, CDCl₃): δ 8.455 (d, 2H); δ 7.81 (m, 2H); δ 7.31–7.26 (m, 2H); δ 2.28 (s, 3H); δ 2.17 (s, 3H): ¹³C NMR (100 MHz, CDCl₃): 149.36, 148.16, 139.36, 138.73, 128.21, 124.27, 123.35, 121.70, 117.15, 112.91, 109.96, 10.63, 7.15. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 190.0980; found, 190.0950.

6.15. 1-Benzyl-4,5-dimethyl-2-phenyl-1H-imidazole 3-Oxide (5a)

Crystal white colored; yield 92%, 256.08 mg; ¹H NMR (400 MHz, CDCl₃): δ 7.59 (d, 2H); δ 7.57–7.34 (m, 3H); δ 7.32–7.26 (m, 3H), δ 6.94 (d, 2H); δ 5.05 (s, 2H); δ 2.27 (s, 3H), δ 2.04 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): 135.81, 134.70, 129.87, 129.79, 129.21, 128.78, 128.04, 126.79, 125.51, 124.23, 120.89, 48.19, 9.13, 7.70. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 279.1497; found, 279.1386.

6.16. 1-Benzyl-4,5-dimethyl-2-(o-tolyl)-1H-imidazole 3-Oxide (5b)

White colored; yield 79%, 230.98 mg; ¹H NMR (400 MHz, CDCl₃): δ 7.34 (d, 1H); δ 7.290–7.205 (m, 5H); δ 7.184 (d, 1H), δ 6.854 (d, 2H); δ 4.901 (q, 2H); δ 2.272 (s, 3H), δ 2.215 (s, 3H), δ 2.114 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): 140.421, 135.507, 135.160, 130.902, 130.724, 130.648, 128.978, 28.017, 126.453, 125.962, 125.897, 123.878, 120.600, 47.859, 19.646, 9.275, 7.626. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 293.1654; found, 293.1593.

6.17. 1-Benzyl-2-(2-hydroxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (5c)

White colored; yield 73%, 214.88 mg; ¹H NMR (400 MHz, CDCl₃): δ 7.406–7.346 (m, 4H), δ 7.140 (d, 1H), δ 7.126 (d, 2H), δ 7.055 (dd, 1H), δ 6.751­(dd, 1H), δ 5.196 (s, 2H), δ 2.300 (s, 3H), δ 2.091 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): 159.827, 136.919, 135.529, 132.131, 129.400, 128.171, 128.079, 125.632, 125.356, 123.347, 121.245, 118.810, 112.142, 48.763, 9.271, 7.472. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 295.1447; found, 295.1379.

6.18. 1-Benzyl-2-(3-hydroxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (5d)

Cream yellow colored, yield 80%, 235.48 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 9.25 (br s, 1H); δ 7.48 (d, 1H); δ 7.36–7.21 (m, 5H); δ 7.14 (s, 1H); δ 6.32 (d, 1H); δ 5.45 (s, 2H); δ 2.92 (s, 3H); δ 2.38 (s, 3H): ¹³C NMR (75 MHz, DMSO-d ₆): 157.56, 144.58, 137.36, 134.25, 130.69, 128.67, 127.55, 125.85, 125.78, 121.45, 115.49, 49.45, 9.47, 7.26. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 295.1447; found, 295.1373.

6.19. 1-Benzyl-4,5-dimethyl-2-(3-nitrophenyl)-1H-imidazole 3-Oxide (5e)

Orange colored, yield 88%, 284.55 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.56 (s, 1H); δ 8.25–8.21 (m, 1H); δ 8.08–8.04 (m, 1H); δ 7.72 (dd, 1H); δ 7.38–7.23 (m, 5H); δ 5.29 (s, 2H); δ 2.14 (s, 3H); δ 2.13 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 148.10, 136.71, 135.48, 131.24, 130.55, 129.91, 129.45, 129.38, 128.95, 128.69, 128.18, 128.13, 127.47, 126.45, 126.37, 126.06, 124.24, 124.09, 123.20, 9.14, 7.85. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 324.1348; found, 324.1309.

6.20. 1-Benzyl-2-(4-hydroxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (5f)

Cream white colored; yield 75%, 220.76 mg; ¹H NMR (300 MHz, CDCl₃): δ 7.31–7.23 (m, 3H), δ 7.025 (dd, 2H), δ 6.897 (d, 2H), δ 6.592 (d, 2H), δ 4.96 (s, 2H), δ 2.26 (s, 3H), δ 2.03 (s, 3H); ¹³C NMR (75 MHz, CDCl₃): 160.80, 137.18, 135.45, 131.44, 129.08, 128.02, 125.91, 125.85, 120.18, 117.31, 112.20, 48.09, 9.09, 7.68. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 295.1447; found, 295.1413.

6.21. 1-Benzyl-2-(2-methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (5g)

White colored; yield 70%, 215.87 mg; ¹H NMR (400 MHz, CDCl₃): δ 7.45–7.36 (m, 2H), δ 7.26–7.16 (m, 3H), δ δ 7.01 (dd, 1H), δ 6.94 (d, 1H), δ 6.87 (d, 2H), δ 4.85 (s, 2H), δ 3.64 (s, 3H), δ 2.22 (s, 3H), δ 2.20 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): 157.89, 135.76, 133.14, 132.26, 132.22, 128.75, 127.71, 126.44, 121.00, 120.53, 113.16, 111.35, 55.40, 48.25, 9.23, 7.68. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 309.1603; found, 309.1582.

6.22. 1-Benzyl-2-(2-chlorophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (5h)

Off white colored, yield 75%, 234.59 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 7.61 (d, 1H); δ 7.55–7.42 (m, 3H); δ 7.27 (p, 3H); δ 6.907 (d, 2H); δ 3.37 (s, 2H), δ 2.11 (s, 3H); δ 2.09 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 136.17, 135.02, 133.67, 132.05, 129.75, 128.95, 128.71, 128.46, 127.60, 127.34, 126.10, 125.26, 124.68, 121.30, 8.79, 7.40. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 313.1108; found, 313.1039.

6.23. 2-(4-Hydroxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8a)

Ivory colored; yield 71%, 145.00 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 9.85 (s, 1H), δ 7.87 (d, 2H), δ 6.77 (d, 2H), δ 2.05 (s, 3H), δ 2.00 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 157.37, 127.28, 115.05, 56.03, 18.56, 11.69, 7.30. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 205.0977; found, 205.0810.

6.24. 2-(2-Hydroxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8b)

Crystal white colored; yield 68%, 138.87 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 9.940 (s, 1H), δ 8.415 (d, 1H), δ 8.140 (dd, 1H), δ 7.785 (d, 1H), δ 7.533 (dd, 1H), δ 1.99 (s, 3H), δ 1.98 (s, 3H): ¹³C NMR (100 MHz, DMSO- d₆): 192.90, 136.22, 134.08, 130.72, 129.11, 128.51, 126.10, 125.47, 124.28, 11.58, 7.23. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 205.0977; found, 205.0908.

6.25. 2-(4-Methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8c)

Cornsilk colored; yield 58%, 126.58 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 7.980 (d, 2H), δ 6.915 (d, 2H), δ 3.770 (s, 3H), δ 2.02 (s, 3H), δ 1.98 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 172.91, 158.64, 135.60, 127.14, 124.40, 122.75, 121.49, 113.55, 11.80, 7.32. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 219.1134; found, 219.0931.

6.26. 2-(2-Methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8d)

Pastel orange colored; yield 54%, 117.85 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 7.79 (s, 1H), δ 7.35 (dd, 1H), δ 7.06 (d, 1H), δ 6.92 (dd, 1H), δ 3.73 (s, 3H), δ 2.06 (s, 3H), δ 1.92 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 156.47, 130.10, 122.81, 119.89, 116.62, 111.28, 55.44, 11.17, 7.11. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 219.1134; found, 219.1039.

6.27. 2-(3-Methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8e)

Ash colored; yield 65%, 141.86 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 10.05 (s, 1H); δ 7.65–7.60 (m, 2H); δ 7.287 (dd, 1H); δ 6.885 (d, 1H), δ 3.76 (s, 3H), δ 2.05 (s, 3H); δ 2.00 (s, 3H): ¹³C NMR (75 MHz, DMSO-d ₆): 193.03, 159.10, 129.36, 117.86, 113.54, 110.74, 55.02, 7.28. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 219.1134; found, 219.0932.

6.28. 4,5-Dimethyl-2-(o-tolyl)-1H-imidazole 3-Oxide (8f)

White colored, yield 72%, 145.62 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 11.10 (s, 1H); δ 7.72 (d, 1H); δ 7.40–7.32 (m, 3H); δ 2.27 (s, 3H); δ 2.06 (s, 3H), δ 1.91 (s, 3H); ¹³C NMR (75 MHz, DMSO-d ₆): 144.58, 137.23,136.49, 134.65, 129.56, 128.66, 127.42, 126.32, 18.56, 10.36, 7.38. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 203.1184; found, 203.1158.

6.29. 4,5-Dimethyl-2-(p-tolyl)-1H-imidazole 3-Oxide (8g)

White colored, yield 76%, 153.71 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 11.12 (s, 1H); δ 7.65 (d, 2H); δ 7.15 (d, 2H); δ 2.25 (s, 3H); δ 2.06 (s, 3H), δ 1.90 (s, 3H); ¹³C NMR (75 MHz, DMSO-d ₆): 143.48, 135.94, 134.65, 128.42, 128.63, 126.31, 121.40, 20.47, 10.34, 7.64. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 203.1184; found, 203.1108.

6.30. 4,5-Dimethyl-2-(3-nitrophenyl)-1H-imidazole 3-Oxide (8h)

Lemon yellow colored; yield 89%, 207.57 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.770 (s, 1H), δ 8.225 (d, 1H), δ 8.100 (dd, 1H), δ 7.613 (dd, 1H), δ 2.05 (s, 3H); δ 2.00 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 147.68, 130.77, 129.84, 124.77, 121.90, 119.15, 11.51, 7.19. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 234.0879; found, 234.0674.

6.31. 4,5-Dimethyl-2-(2-nitrophenyl)-1H-imidazole 3-Oxide (8i)

Mustard yellow colored; yield 95%, 221.56 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 11.750 (s, 1H); δ 7.950 (d, 1H); δ 7.756 (dd, 1H), δ 7.680 (d, 1H), δ 7.623 (dd, 1H), δ 2.05 (s, 3H); δ 2.01 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 148.06, 134.46, 132.82, 131.26, 129.42, 124.22, 7.30. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 234.0879; found, 234.0822.

6.32. 2-(4-Chlorophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8j)

White colored, yield 85%, 189.27 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 7.98 (d, 2H), δ 7.42 (d, 2H), δ 2.02 (s, 3H), δ 2.00 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 134.63, 132.62, 131.56, 129.02, 128.77, 127.43, 127.21, 125.76, 124.39, 12.04, 7.71. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 223.0638; found, 223.0543.

6.33. 2-(3-Chlorophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8k)

White colored; yield 87%, 193.72 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.105 (d, 1H), δ 7.960 (d, 1H), δ 7.450–7.310 (m, 2H), δ 2.06 (s, 6H); ¹³C NMR (100 MHz, DMSO-d ₆): 133.60, 130.71, 127.67, 25.17, 124.18, 100.01, 7.82HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 223.0638; found, 223.0571.

6.34. 2-(3-Formylphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8l)

Light yellow colored; yield 90%, 194.61 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 14.710 (s, 1H), δ 12.680 (s, 1H), δ 7.45 (d, 1H), δ 7.30 (dd, 1H), δ 6.89–6.83 (m, 2H), δ 2.20 (s, 3H), δ 2.10 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 158.32, 133.95, 131.44, 127.36, 123.88, 122.19, 119.55, 118.14, 113.05, 9.95, 9.70. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 217.0977; found, 217.0970.

6.35. 2-(Furan-2-yl)-4,5-dimethyl-1H-imidazole 3-Oxide (8m)

Brown colored; yield 84%, 149.68 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 7.690 (dd, 1H); δ 6.845 (d, 1H); δ 6.552 (dd, 1H), δ 2.03 (s, 3H); δ 2.00 (s, 3H); ¹³C NMR (75 MHz, DMSO-d ₆): 142.85, 142.42, 130.07, 125.60, 122.91, 111.53, 108.02, 11.83, 7.10. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 179.0821; found, 179.0783.

6.36. 4,5-Dimethyl-2-phenyl-1H-imidazole 3-Oxide (8n)

Crystal white colored; yield 91%, 171.28 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 7.97 (d, 2H), δ 7.37–7.26 (m, 3H), δ 2.00 (s, 3H), δ 1.94 (s, 3H): ¹³C NMR (75 MHz, DMSO-d ₆): 135.26, 128.25, 127.92, 127.84, 125.69, 124.58, 123.82, 11.44, 7.19. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 189.1028; found, 189.0921.

6.37. 2-(3-Hydroxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8o)

White colored, yield 81%, 164.42 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 10.150 (s, br s,1H); δ 7.730 (s, 1H); δ 7.415 (d, 1H); δ 7.170 (dd, 2H); δ 6.720 (q, 1H); δ 2.050 (s, 3H); δ 1.990 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 157.91, 135.08, 129.71, 124.35, 116.64, 115.59, 113.09, 11.72, 7.65. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 205.0977; found, 205.0889.

6.38. 2-(2-Chlorophenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (8p)

Creamy white colored; yield 82%, 182.59 mg; ¹H NMR (300 MHz, CDCl₃): δ 12.51 (s, 1H), δ 7.26–7.12 (m, 2H), δ 7.04 (d, 1H), δ 6.97 (dd, 1H), δ 1.69 (s, 3H); δ 1.63 (s, 3H); ¹³C NMR (75 MHz, CDCl₃): 134.10, 132.93, 132.23, 130.35, 129.48, 126.41, 123.75, 122.97, 10.22, 6.82. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 223.0638; found, 223.0560.

6.39. 1-Hydroxy-4,5-dimethyl-2-(3-nitrophenyl)-1H-imidazole 3-Oxide (11a)

Yellow colored; yield 84%, 209.35 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.78 (s, 1H), δ 8.46 (m, 1H), δ 8.39 (m, 1H), δ 7.93 (dd, 1H), δ 2.28 (s, 6H); ¹³C NMR (100 MHz, DMSO-d ₆): 148.13, 135.79, 131.75, 131.13, 126.37, 124.38, 123.41, 122.13, 7.57. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 250.0828; found, 250.0640.

6.40. 1-Hydroxy-2-(2-hydroxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (11b)

White colored, yield 67%, 147.55 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 11.375 (s, 1H); δ 7.69 (s, 1H); δ 7.36 (t, 1H); δ 6.92 (dd, 2H); δ 2.195 (s, 6H); ¹³C NMR (75 MHz, DMSO-d ₆): 159.21, 159.52, 132.02, 131.90, 129.34, 121.54, 120.24, 118.44, 111.92, 9.80, 7.57. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 221.0926; found, 221.0829.

6.41. 1-Hydroxy-2-(4-methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (11c)

Crystal White colored, yield 61%, 142.89 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 13.49 (s, 1H), 7.93 (d, 2H), 7.19 (d, 2H), 3.86 (s, 3H), 2.26 (s, 6H)·¹³C NMR (100 MHz, DMSO-d ₆): δ 162.13, 134.89, 131.91, 122.42, 114.99, 112.59, 56.14, 7.70. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 235.1083; found, 235.0985.

6.42. 1-Hydroxy-4,5-dimethyl-2-(o-tolyl)-1H-imidazole 3-Oxide (11d)

White colored, yield 71%, 154.96 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 13.42 (br s, 1H); δ 10.34 (s, 1H); δ 7.55 (m, 1H); δ 2.275 (s, 5H): ¹³C NMR (100 MHz, DMSO-d ₆): 139.86, 135.22, 132.42, 132.04, 130.92, 126.40, 122.67, 120.56, 19.88, 7.75. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 219.1134; found, 219.1094.

6.43. 1-Hydroxy-4,5-dimethyl-2-(p-tolyl)-1H-imidazole 3-Oxide (11e)

Crystal White colored, yield 74%, 161.51 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 13.59 (br s, 1H); δ 7.87 (t, 2H); δ 7.415 (d, 2H); δ 2.39 (s, 3H); δ 2.26 (s, 6H): ¹³C NMR (100 MHz, DMSO-d ₆): 153.48, 142.27, 134.80, 129.96, 129.89, 129.80, 122.62, 117.66, 21.62, 9.81, 7.68. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 219.1134; found, 219.1060.

6.44. 2-(2-Chlorophenyl)-1-hydroxy-4,5-dimethyl-1H-imidazole 3-Oxide (11f)

White colored, yield 79%, 188.55 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 7.69 (s, 1H); δ 6.845 (d, 2H); δ 6.555 (d, 1H); δ 2.03 (s, 3H); δ 2.00 (s, 3H): ¹³C NMR (100 MHz, DMSO-d ₆): 142.13, 142.41, 130.12, 125.68, 122.85, 111.53, 107.96, 11.89, 7.12. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 239.0587; found, 239.0550.

6.45. 2-(4-Chlorophenyl)-1-hydroxy-4,5-dimethyl-1H-imidazole 3-Oxide (11g)

White colored, yield 82%, 195.71 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 10.36 (s, 1H), 8.04 (d, 2H), 7.73 (d, 2H), 2.29 (s, 6H). ¹³C NMR (100 MHz, DMSO–D6-d ₆): δ 137.05, 133.65, 131.95, 129.60, 123.22, 119.58, 7.80. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 239.0587; found, 239.0549.

6.46. 2-(3-Chlorophenyl)-1-hydroxy-4,5-dimethyl-1H-imidazole 3-Oxide (11h)

White colored, yield 87%, 207.64 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 10.33 (br s, 1H); δ 8.05 (d, 2H); δ 7.915 (d, 2H); δ 7.68–7.59 (m, 2H); δ 2.22 (s, 6H); ¹³C NMR (100 MHz, DMSO-d ₆): 133.74, 132.88, 131.84, 131.23, 129.46, 128.63, 123.20, 122.38, 7.75. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 239.0587; found, 239.0489.

6.47. 2-(Furan-2-yl)-1-Hydroxy-4,5-dimethyl-1H-imidazole 3-Oxide (11i)

Gray colored, yield 88%, 170.89 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.11 (s, 1H); δ 7.345 (s, 1H); δ 6.82 (s, 1H); δ 2.24 (s, 6H): ¹³C NMR (100 MHz, DMSO-d ₆): 147.16, 135.39, 127.37, 123.30, 117.05, 112.79, 7.68. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 195.0770; found, 195.0685.

6.48. 1-Hydroxy-4,5-dimethyl-1H-imidazole 3-Oxide (11j)

White colored, yield 96%, 123.00 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 11.41 (s, 1H), 9.06 (s, 1H), 2.00 (s, 6H). ¹³C NMR (100 MHz, D₂O): δ 122.38, 121.69, 6.19. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 129.0664; found, 129.0647.

6.49. 1-Hydroxy-2-(2-methoxyphenyl)-4,5-dimethyl-1H-imidazole 3-Oxide (11k)

Crystal White colored, yield 58%, 135.86 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 13.23 (br s, 1H); δ 7.77 (d, 1H); δ 7.49 (dd, 1H); δ 7.19–7.15 (m, 2H); δ 3.72 (s, 3H); δ 2.27 (s, 6H): ¹³C NMR (75 MHz, DMSO-d ₆): 158.46, 134.43, 132.85, 122.71, 120.82, 112.55, 109.14, 56.52, 7.79. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 235.1083; found, 235.0976.

6.50. 1-Hydroxy-4,5-dimethyl-2-phenyl-1H-imidazole 3-Oxide (11l)

White colored, yield 94%, 191.97 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 13.62 (s, 1H), 8.02–7.92 (m, 2H), 7.65 (dd, 3H), 2.28 (s, 6H)·¹³C NMR (100 MHz, DMSO): δ 137.05, 133.65, 131.95, 129.60, 123.22, 119.58, 7.80. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 205.0977; found, 205.0872.

6.51. 1-Benzyl-4,5-diphenyl-1H-imidazole 3-Oxide (14a)

White colored, yield 94%, 306.81 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.68 (s, 1H); δ 7.492 (m, 2H); δ 7.38 (q, 3H); δ 7.29–7.22 (m, 8H); δ 6.97 (q, 2H); δ 5.07 (s, 2H); ¹³C NMR (100 MHz, DMSO-d ₆): 136.23, 130.76, 129.43, 129.13, 128.96, 128.66, 127.70, 127.63, 127.60, 126.52, 48.63. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 327.1497; found, 327.1432.

6.52. 1-(4-Methoxyphenyl)-4,5-diphenyl-1H-imidazole 3-Oxide (14b)

Lavender colored, yield 97%, 331.87 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.77 (s, 1H); δ 7.51 (d, 2H); δ 7.29–7.16 (m, 10H); δ 6.93 (d, 2H); δ 3.73 (s, 3H); ¹³C NMR (100 MHz, DMSO-d ₆): 159.13, 130.87, 129.54, 128.96, 128.56, 127.97, 127.81, 127.69, 126.55, 114.36, 55.48. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 343.1447; found, 343.1434.

6.53. 1,4,5-Triphenyl-1H-imidazole 3-Oxide (14c)

Off white colored, yield 90%, 281.13 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 8.87 (s, 1H); δ 7.84 (d, 2H); δ 7.74 (d, 2H); δ 7.62–7.38 (m, 11H); ¹³C NMR (100 MHz, DMSO-d ₆): 134.96, 130.86, 129.62, 129.32, 129.03, 128.61, 127.98, 127.82, 126.45, 114.64. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calculated 313.1341; found, 313.1258.

6.54. 4,5-Diphenyl-1H-imidazole 3-Oxide (14d)

White colored, yield 91%, 215.01 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 7.81 (s, 1H); δ 7.44–7.34 (m, 7H); δ 7.25–7.19 (m, 2H); δ 7.17–7.11 (m, 1H); ¹³C NMR (100 MHz, DMSO-d ₆): 172.58, 135.17, 132.80, 132.49, 130.15, 129.29, 128.50, 128.18, 128.02, 126.30, 126.22, 125.96. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 237.1028; found, 237.0965.

6.55. 1-Hydroxy-4,5-diphenyl-1H-imidazole 3-Oxide (14e)

White colored, yield 92%, 232.09 mg; ¹H NMR (400 MHz, DMSO-d ₆): δ 10.40 (s, 1H); δ 10.11 (s, 1H); δ 7.48–7.36 (m, 9H); ¹³C NMR (100 MHz, DMSO-d ₆): 130.44, 130.00, 129.01, 128.79, 128.69, 127.69, 126.40, 123.94. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 253.0977; found, 253.0890.

6.56. 2-(2-Chlorophenyl)-1-hydroxy-p4,5-diphenyl-1H-imidazole 3-Oxide (14f)

White colored, yield 92%, 333.79 mg; ¹H NMR (300 MHz, DMSO-d ₆): δ 12.42 (s, 1H); δ 7.84 (m, 4H); δ 7.71–7.49 (m, 8H); δ 7.38 (m, 2H); ¹³C NMR (75 MHz, DMSO-d ₆): 141.34, 137.78, 137.69, 133.45, 133.04, 132.25, 130.15, 129.54, 129.32, 129.14, 129.10, 128.98, 128.75, 128.74, 127.54, 127.52, 127.51, 127.50, 127.35. HRMS (ESI/Q-TOF) m/z: [M + H]⁺ calcd 363.0900; found, 363.0881.

The data supporting this article have been included as part of the Supporting Information. The crystallographic data for compound 8m are available at https://www.ccdc.cam.ac.uk, which have been deposited at the CCDC under CCDC no. 2498368.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c13523.

• Experimental details, theoretical investigation, synthetic procedure for various imidazole N-oxide derivatives, Sc-XRD experimental data, and copies of ¹H, ¹³C NMR spectra and HRMS for all isolated compounds (DOCX)

Kaberi SikdarFormal analysis, Investigation, Methodology, Visualization, Writingoriginal draft. Manirul MandalData analysis, Investigation, Methodology. Hari Sankar DasData analysis, Investigation. Gouhar Jahan AshrafFormal analysis, Methodology. Pintu PratiharData analysis, Validation. Sangita DeyFormal analysis, Methodology. Mohabul Alam MondalData analysis, Validation. Ranabir SahuData analysis, Validation, Investigation. Anoop KumarData analysis, Validation, Investigation. Dilip Kumar MaitiData analysis, Validation, Visualization, Writingreview and editing. Mossaraf HossainFormal analysis, Conceptualization, Investigation, Supervision, Validation, Visualization, Writingoriginal draft, Writingreview and editing.

The authors declare no competing financial interest.