5-Hydroxymethylfurfural-Derived Boron-Dipyrromethene Immobilized on Resin Support as a Sustainable Catalyst for C–H Arylation of Heterocycles

Abstract

5-Hydroxymethylfurfural (HMF) was used as a sustainable raw material in the development of a resin-supported boron-dipyrromethene (BODIPY)-based photocatalyst. In the development of the catalyst, the brominated product (HMF-BODIPY-Br) and photocatalyst (HMF-BODIPY-Br-Suc) were isolated under a chromatography-free condition. The photocatalyst was loaded on polymeric resin by bridging alcohol functionality in HMF and amine functionality in polymeric resin using succinic anhydride. The resin-supported photocatalyst was used in light-mediated C–H arylation of various heterocycles using aryldiazonium salt. For representative examples, diazotization and photoarylation were carried out in one pot, and arylated furans were obtained in very good yields. C–H arylation was found to proceed via a photogenerated radical intermediate, and the radical intermediate was trapped by forming an adduct with TEMPO.

Introduction

The ever-increasing demand for fossil-sourced energy and chemical products results in depletion of fossil fuel reserves, impacting environmental harmony. Intense research is being carried out on developing many plant-sourced organic matters as energy alternates to be used in internal combustion engines, for example, ethanol,¹ biodiesel,²⁻⁴ and 2,5-dimethylfuran.⁵⁻⁷ Considering the demand for fine chemicals, various HMF-derived chemicals have been utilized as plant-sourced sustainable raw materials (Table 1).^8,9

Table 1. 5-Hydroxymethylfurfural (HMF)-Derived Fine Chemicals.

entry	fine chemical	utilization
1	DFF10−12	pharmaceutical intermediates and antifungal agents
2	FDCA13−16	biorenewable alternate for fossil-derived terephthalic acid
3	BHF17,18	monomer for polyurethane foams and polyesters
4	BAF19,20	monomer for polyamides and polyurethanes
5	caprolactone21	monomer for production of nylon-6
6	1,6-hexanediol22,23	monomer for polyurethane foams and polyesters
7	adipic acid24	monomer for production of nylon

HMF-derived 2,5-diformylfuran (DFF) has been utilized as a raw material in accessing pharmaceutical intermediates and antifungal agents.¹⁰⁻¹² 2,5-Furandicarboxylic acid (FDCA) accessed by oxidation of HMF is an alternate for fossil-derived terephthalic acid in making polymers.¹³⁻¹⁶ 2,5-Bis(hydroxymethyl)furan (BHF) obtained by reduction of HMF is used as a monomer in the synthesis of polyurethane foams and polyesters.^17,18 2,5-Bis(aminomethyl)furan (BAF) is used as a monomer in the synthesis of polyamides and polyurethanes.^19,20 Caprolactone, an important molecule in polymer industry, can be obtained from HMF.²¹ HMF-derived 1,6-hexanediol has been utilized as a monomer in the synthesis of polyurethane foams and polyesters.^22,23 HMF can also be utilized in the synthesis of adipic acid, a monomer utilized in the production of nylon.²⁴ To date, HMF has been converted into many simple molecules of industrial importance, including DFF, FDCA, etc.²⁵ The use of HMF in developing complex functional molecules has not been explored much. Herein, we have taken a step ahead to utilize HMF beyond its conventional usage of accessing simple molecules. We have developed a functionalized photocatalyst accessible from sustainable raw materials such as HMF and 2,4-dimethylpyrrole. The photocatalyst has been immobilized on polymeric resin to facilitate its complete recovery after the reaction. The immobilized photocatalyst has been utilized in light-mediated arylation of various arenes. Recovery and reusability of the resin-supported photocatalyst have been demonstrated.

Results and Discussion

Previously, we have developed a facile method to access HMF from fructose at room temperature, utilizing silica as a solid support, mitigating humin formation, and facilitating selective extraction of HMF.²⁶ Also, we have strategically utilized 2,4-dimethylpyrrole (DMP) in developing a colorimetric naked-eye chemosensor for copper(II) ions.^27,28 Here, we have utilized these two sustainable raw materials (HMF and DMP) in developing a sustainable photocatalyst with an objective to mitigate our dependency on fossil-based chemicals. A retrosynthetic scheme originating from sustainable raw materials including 5-hydroxymethylfurfural (HMF), succinic anhydride, and 2,4-dimethylpyrrole was designed to access the photocatalyst (Scheme 1).

Scheme 1. Sustainable Raw Materials Utilized in Synthesis of Photocatalyst.

HMF was converted into BODIPY alcohol (HMF-BODIPY) in a three-step process (Scheme 2). In the first step, HMF was converted into corresponding 1,3,7,9-tetramethyl-dipyrromethane (TM-DPM). The formed TM-DPM was further oxidized into corresponding dipyrrin using chloranil as an oxidant and then treated with excess BF₃·OEt₂ in basic media. All these three steps are low yielding synthetic steps. On carrying out these three steps in one pot, HMF-BODIPY was obtained in 5% overall yield. Our attempts to increase the yield of HMF-BODIPY did not succeed. Hence, we proceeded further for functionalization of HMF-BODIPY and immobilization of the photocatalyst on polymeric resin.

Scheme 2. Synthesis of HMF-derived BODIPY Alcohol.

Visible light-mediated reactions attract considerable attention.²⁹⁻³¹ BODIPY derivatives have been previously utilized as photocatalysts in various organic transformations.^32,33 In general, bromination of BODIPY increases the population at the triplet excited state by spin–orbit coupling.³⁴⁻³⁶ Hence, we have brominated HMF-BODIPY in positions 2 and 6 using N-bromosuccinimide under chromatography-free synthesis and obtained HMF-BODIPY-Br in a quantitative yield (Scheme 3). The byproduct, succinimide, was removed by washing with water. Then, acid functionality was introduced into HMF-BODIPY-Br by treating with excess succinic anhydride. Complete consumption of HMF-BODIPY-Br was confirmed by TLC analysis. Excess succinic anhydride was removed by washing with warm water. Trituration of the organic layer with hexanes yielded HMF-BODIPY-Br-Suc in pure form (63% yield), without any chromatographic purification.

Scheme 3. Synthesis of HMF-BODIPY-Br-Suc and Immobilization on Polymeric Resin.

The UV–vis spectrum of the photocatalyst showed maximum absorption at 545 nm. Coupling reagents that used to immobilize the photocatalyst on resin did not show any absorption near 545 nm (Supporting Information). Hence, we decided to utilize this absorption characteristics of HMF-BODIPY-Br-Suc (ϵ = 35,100 M^–1 cm^–1) to estimate the extent of loading in the process of immobilization of the photocatalyst on polymeric resin, aminomethyl polystyrene (Scheme 3). The amino functionality on the resin was coupled with acid functionality of HMF-BODIPY-Br-Suc via an amide linkage utilizing peptide-coupling reagents. The extent of immobilization on polymeric resin was calculated based on (i) absorbance of unreacted HMF-BODIPY-Br-Suc present in a reaction medium and (ii) change in the weight of resin after BODIPY loading.

HMF-BODIPY-Br-Suc shows strong absorption at 545 nm (ϵ = 35,100 M^–1 cm^–1) in the free state and after immobilization on polymeric resin (Supporting Information). Hence, we have used green LED, emitting in the range between 495 and 555 nm with a maximum at 520 nm, as a light source for photocatalysis (Figure 1).

Figure 1.

Emission spectrum of green LED.

The immobilized photocatalyst was utilized in green light-mediated arylation of heteroarenes and arenes using aryldiazonium salt. Initially, photoarylation was explored in furan. In a typical experiment, a mixture of aryldiazonium tetrafluoroborate, furan, and the photocatalyst in a solvent was irradiated with green LED at 30 °C for 2 h. We have observed in a solvent screening study that the yield of the photoarylation product is directly depending on the solubility of aryldiazonium salt. 4-Bromobenzenediazonium tetrafluoroborate is completely soluble in dimethylsulfoxide (DMSO), least soluble in halogenated solvents such as dichloroethane (DCE) and dichloromethane (DCM), and moderately soluble in other polar solvents such as acetone, acetonitrile, and ethanol. Among the various solvents utilized for photoarylation of furan, better yields were obtained in the DMSO solvent (Table 2). Control experiments were carried out in the absence of the photocatalyst or without irradiation. The formation of the product in a very low yield (10%) in the absence of the photocatalyst confirmed the importance of the photocatalyst in mediating photoarylation (Table 2, entry 7). In the absence of light and both photocatalyst and light, the product was obtained in traces (Table 2, entries 8 and 9).

Table 2. Solvent Screening in Immobilized BODIPY-Catalyzed Photoarylation^a.

entry	solvent	yield (%)
1	acetone	59
2	acetonitrile	61
3	ethanol	54
4	DCE	21
5	CH2Cl2	16
6	DMSO	73
7	DMSO	10b
8	DMSO	in tracesc
9	DMSO	in tracesd

^aA mixture of 4-bromobenzenediazonium tetrafluoroborate (0.25 mmol), immobilized photocatalyst (5 mg, ∼3.6 μmol), and furan (1.0 mL) in solvent (2.0 mL) stirred under green LED at 30 °C for 2 h.

^bExperiment was carried out in the absence of photocatalyst.

^cExperiment was carried out without irradiation.

^dWithout irradiation, in the absence of photocatalyst.

To study the substrate scope of this photoarylation, experiments were carried out using different arenes and diazonium salts (Table 3). The reaction condition utilized in the photoarylation of furan using 4-bromobenzenediazonium tetrafluoroborate (Table 2, entry 5) was adopted in the arylation of furan using other diazonium salts (Table 3, entries 1–6). Corresponding 2-arylfurans were obtained in moderate to good yields. Further, we extended this methodology to arylate thiophene. In the case of arylation of thiophene using 4-chlorobenzenediazonium tetrafluoroborate, the arylated product was obtained in a low yield (30%) upon 2 h irradiation (Table 2, entry 7). Extending the irradiation time to 4 h increased the product yield (Table 3, entries 8 and 9). We further explored the photoarylation of benzene as a representative example of simple arenes using different diazonium salts (Table 3, entries 10–14). Photoarylation of benzene was sluggish, and even after 12 h irradiation, different biphenyls were obtained in lower yields (Table 3, entries 12–14). The photocatalyst system was found to be effective in light-mediated arylation of heteroarenes. In photoarylation using a radical scavenger TEMPO, the radical-scavenged product 2,2,6,6-tetramethyl-1-(4-nitrophenoxy)piperidine was obtained in 80% yield. This experiment affirmed that the photoarylation proceeds via a radical intermediate (Scheme 4).

Table 3. Substrate Scope in Immobilized BODIPY-Catalyzed Photoarylation^a.

^aA mixture of aryldiazonium tetrafluoroborate (0.25 mmol), photocatalyst (5 mg, ∼3.6 μmol), and furan/benzene (1.0 mL) or thiophene (1.25 mmol) in DMSO (2.0 mL) stirred under green LED at 30 °C for stipulated time.

Scheme 4. Photoarylation via Radical Intermediate.

Recoverability and recyclability are another attracting features of the immobilized catalyst system. We have studied the recyclability of the newly developed pseudo-homogeneous immobilized photocatalyst (Table 4). In a solvent medium, the immobilized photocatalyst swells and behaves as a homogeneous-like system. After the completion of the reaction, the photocatalyst was recovered by simple filtration. The recovered catalyst was reused in four recycles of photoarylation and found to be effective in catalyzing photoarylation with out any deterioration in yield (Table 4).

Table 4. Catalyst Recyclability in Photoarylation of Furan^a.

entry	cycle number	yield (%)
1	fresh catalyst	76
2	I recycle	78
3	II recycle	76
4	III recycle	71
5	IV recycle	71

^aA mixture of 4-chlorobenzenediazonium tetrafluoroborate (57 mg, 0.25 mmol), fresh/recovered catalyst (5 mg, ∼3.6 μmol), and furan (1.0 mL) in DMSO (2.0 mL) stirred under green LED at 30 °C for 2 h.

Further, we have explored the in situ diazotization and photoarylation in one pot for representative substituted anilines (Table 5). tert-Butyl nitrite was used to diazotize p-substituted anilines.³⁷ In our first exploration on in situ diazotization and photoarylation, a mixture containing 4-chloroaniline, the resin-supported photocatalyst, and furan in DMSO was irradiated using green LED at 30 °C for 2 h. It is interesting to note that the product 2-(4-chlorophenyl)furan was obtained in 56% yield (Table 5, entry 1). When we treat 4-nitroaniline with furan under the same reaction condition, 2-(4-nitrophenyl)furan was obtained in 71% yield (Table 5, entry 2). In the photoarylation using diazonium salt, we are constrained to use DMSO due to poor solubility of diazonium salt in other solvents. In in situ diazotization and photoarylation, we have explored the use of dichloromethane (DCM) as a solvent. While we used DCM as a solvent in the photoarylation of furan using 4-nitroaniline, we have observed a slight decrease in yield, and the product was obtained in 62% yield (Table 5, entry 3). Hence, we can avoid the use of DMSO as a solvent in photoarylation by adopting in situ diazotization and photoarylation strategies. In the absence of t-BuONO, the arylated product was not formed (Table 5, entry 4).

Table 5. In Situ Diazotization in Photoarylation of Furan^a.

entry	R	solvent	yield (%)
1	–Cl	DMSO	56
2	–NO2	DMSO	71
3	–NO2	DCM	62
4	–NO2	DCM	not formedb

^aA mixture of p-substituted aniline (0.25 mmol), t-BuONO (57 μL, 0.50 mmol), resin-supported photocatalyst (5 mg, ∼3.6 μmol), and furan (1.0 mL) in a solvent (2.0 mL) stirred under green LED at 30 °C for 2 h.

^bIn the absence of t-BuONO.

Conclusions

We have developed a pseudo-homogeneously immobilized BODIPY-based photocatalyst from sustainable raw materials, 5-hydroxymethylfurfural and 2,4-dimethylpyrrole. The extent of loading was measured based on optical intensity of the unreacted photocatalyst present in a reaction medium. The immobilized photocatalyst was employed in C–H arylation of heteroarenes and simple arenes. The catalyst was recovered from a reaction medium by simple filtration. The recovered catalyst was found to be effective in all four recycles tested. DMSO was used as a solvent to facilitate the dissolution of diazonium salt. By adopting in situ diazotization and photoarylation strategies, the use of DMSO as a solvent can be avoided.

Experimental Section

General Information

¹H NMR (300 MHz) spectra were recorded using a Bruker 300 AVANCE II spectrometer, with chloroform-d as a solvent and tetramethylsilane (TMS) as a reference (δ = 0 ppm). The chemical shifts are expressed in δ downfield from the signal of internal TMS. Mass spectra were measured on a Shimadzu-Kratos-Axima CFR+ MALDI-TOF spectrometer. Analytical thin layer chromatographic tests were carried out on aluminium sheets coated with silica gel GF provided by Merck. The spots were visualized using UV light. Column chromatography was carried out using silica gel (230–400 mesh). All yields reported are of isolated materials judged to be homogeneous using TLC and NMR spectroscopy. Aryldiazonium tetrafluoroborates,³⁸ HMF,^26,39 and 2,4-dimethylpyrrole⁴⁰ were synthesized by a reported procedure. (Aminomethyl)polystyrene (70–90 mesh, 1% cross-linked) was purchased from Sigma-Aldrich.

8-(5-Hydroxymethyl-2-furanyl)-1,3,5,7-tetramethylBODIPY (HMF-BODIPY)

A solution of HMF (8.0 mmol, 1.0 g) in CH₂Cl₂ (5.0 mL) was added in drops to a mixture containing 2,4-dimethylpyrrole (24 mmol, 2.4 mL), celite (50 mg), and CH₂Cl₂ (10 mL) and stirred for 1 h at 30 °C under N₂. After the complete consumption of HMF as evidenced by TLC analysis, the reaction mixture was diluted with hexane (20 mL) and filtered. The filtrate was concentrated under reduced pressure. The resulting reddish brown solid was dissolved in toluene (100 mL) and then treated with chloranil (8.8 mmol, 2.2 g, 1.1 equiv) at 30 °C for 45 min. To the reaction mixture, Et₃N (7.8 mL, 56 mmol, 7.0 equiv) was added and stirred for 10 min. After 10 min, BF₃·OEt₂ (7.1 mL, 56 mmol, 7.0 equiv) was added in drops to the cooled reaction mixture. The stirring was continued for 15 h, and the corresponding BODIPY formation was confirmed by TLC analysis using a hexane/EtOAc (1:1, v/v) mixture as an eluent. Then, the toluene layer from the reaction mixture was decanted. The remaining viscous mass in the reaction flask was washed with toluene (2 × 25 mL). The combined toluene extract was washed with water, saturated with NaCl solution, dried with anhydrous sodium sulfate, and filtered. The filtrate was concentrated under reduced pressure. The resulting solid was purified by column chromatography [silica, (30% EtOAc + 70% hexane)] to obtain the title compound as a red color solid (138 mg, 5% yield). ¹H NMR (300 MHz, CDCl₃, δ): 1.65 (s, 6H), 2.55 (s, 6H), 4.68 (s, 2H), 6.02 (s, 2H), 6.42 (dd, J₁ = 11.4 Hz, J₂ =3.0 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 13.2, 14.7, 57.3, 109.3, 112.2, 121.4, 127.9, 132.8, 143.0, 145.0, 155.1, 157.0; MALDI-TOF-MS obsd 344.5851, calcd 344.1508 (M = C₁₈H₁₉BF₂N₂O₂).

2,6-Dibromo-8-(5-hydroxymethyl-2-furanyl)-1,3,5,7-tetramethyl-BODIPY (HMF-BODIPY-Br)

N-Bromosuccinimide (171 mg, 0.96 mmol, 3.0 equiv) was added to a stirred solution of 8-(5-hydroxymethyl-2-furanyl)-1,3,5,7-tetramethyl-BODIPY (110 mg, 0.32 mmol) in dry CH₂Cl₂ at 0 °C. The resulting reaction mixture was warmed to 30 °C and stirred for 30 min under N₂. Then, the reaction mixture was washed with water and saturated with NaCl solution. The organic layer was dried with sodium sulfate, and the solvent was removed by rotary evaporation under reduced pressure to obtain 2,6-dibromo-8-(5-hydroxymethyl-2-furanyl)-1,3,5,7-tetramethyl-BODIPY (159 mg, 99% yield). The sample was pure enough to proceed to the next step as judged by NMR analysis. ¹H NMR (300 MHz, CDCl₃, δ): 1.64 (s, 6H), 2.60 (s, 6H), 4.70 (s, 2H), 6.46 (dd, J₁ = 13.8 Hz, J₂ =3.0 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃ δ): 12.7, 13.9, 57.3, 109.5, 112.1, 113.0, 128.2, 131.7, 140.5, 144.2, 155.4, 155.7; MALDI-TOF-MS obsd 502.7312, calcd 501.9697 (M = C₁₈H₁₇BBr₂F₂N₂O₂).

2,6-Dibromo-1,3,5,7-tetramethyl-8-(5-succinyloxymethyl-2-furanyl)BODIPY (HMF-BODIPY-Br-Suc)

The sample from the previous step (150 mg) and succinic anhydride (192 mg, 1.9 mmol, 6.0 equiv) were dissolved in dry CH₂Cl₂ (15 mL) and treated with Et₃N (0.178 mL, 1.3 mmol, 4.0 equiv). The resulting reaction mixture was stirred at 30 °C under N₂ until the complete consumption of 2,6-dibromo-8-(5-hydroxymethyl-2-furanyl)-1,3,5,7-tetramethyl-BODIPY as judged by TLC analysis (∼30 min). Then, the reaction mixture was diluted with CH₂Cl₂ (10 mL) and washed with warm water to remove excess succinic anhydride. The organic layer was washed with saturated NaCl solution and dried with anhydrous sodium sulfate. The solvent was removed under reduced pressure. The resulting residue was dissolved in a minimum amount of CH₂Cl₂ and triturated with hexane. The resulting precipitate was removed by filtration and dried under reduced pressure to obtain 2,6-dibromo-1,3,5,7-tetramethyl-8-(5-succinyloxymethyl-2-furanyl)BODIPY as a purple solid (120 mg, 63% yield). ¹H NMR (300 MHz, CDCl₃, δ): 1.61 (s, 6H), 2.60 (s, 6H), 2.62–2.72 (m, 4H), 5.16 (s, 2H), 6.46 (d, J =3.3 Hz, 1H), 6.60 (d, J =3.3 Hz, 1H); ¹³C NMR (75 MHz, CDCl₃, δ): 12.6, 13.9, 28.5, 28.7, 58.0, 112.5, 113.1, 127.8, 131.7, 140.5, 145.0, 150.8, 155.5, 171.6, 176.6; MALDI-TOF-MS obsd 602.8744, calcd 601.9858 (M = C₂₂H₂₁BBr₂F₂N₂O₅).

Epsilon Value Calculation for HMF-BODIPY-Br-Suc

For the epsilon value calculation, a stock solution (200 μM) was prepared by dissolving HMF-BODIPY-Br-Suc (3.0 mg, 5.0 μmol) in CH₃CN (25 mL). Solutions of HMF-BODIPY-Br-Suc of different concentrations (6.6, 13, 20, 27, 33 μM) were prepared from stock solution. For the prepared solutions, the absorbance at a λ_max value of 545 nm was measured by UV–vis spectroscopy. From the slope of the plot (concentration vs absorbance at 545 nm), the ϵ value was determined to be 35,100 M^–1 cm^–1.

Loading of HMF-BODIPY-Br-Suc on Resin

DIPEA (21 μL, 120 μmol, 2.0 equiv) was added to a stirred suspension of (aminomethyl)polystyrene resin (40 mg, 60 μmol), HMF-BODIPY-Br-Suc (36 mg, 60 μmol), and HBTU (34 mg, 90 μmol, 1.5 equiv) in dry CH₂Cl₂ (2.0 mL). The reaction mixture was stirred at 30 °C under N₂ for 12 h. The change in the color of resin from translucent to dark red affirmed the loading of BODIPY on resin. The extent of loading of BODIPY on resin was calculated by measuring the absorbance of the reaction mixture. After 12 h, the resin loaded with BODIPY was separated by filtration. On the basis of the absorbance value of the filtrate at 545 nm, the amount of unreacted BODIPY was found to be 8.5 μmol. Hence, the percentage of loading was found to be 85.8%. The resin loaded with BODIPY was washed throughly and dried under reduced pressure to obtain BODIPY immobilized on resin (72 mg). On the basis of the increase in the weight of resin, the percentage of loading was found to be 88%. This loading value was utilized in calculating the amount of BODIPY present in 5 mg of immobilized photocatalyst as 3.6 μmol.

General Procedure for Arylation of Furan

Aryldiazonium tetrafluoroborate (0.25 mmol) was added to a stirred suspension of furan (1.0 mL) and HMF-BODIPY-loaded resin (5 mg, ∼3.6 μmol) in DMSO (2.0 mL). The reaction mixture was stirred under irradiation of green LED at 30 °C for 2 h. Then, the catalyst was separated by filtration and washed with diethyl ether for further reuse. The combined filtrate was diluted with diethyl ether, washed with water, and dried with anhydrous sodium sulfate. The solvent was removed under reduced pressure. The resulting residue was purified using column chromatography to obtain arylated furan in pure form.

2-Phenylfuran

(20 mg, 56%); ¹H NMR (300 MHz, CDCl₃, δ): 6.47 (dd, J₁ = 1.8 Hz, J₂ = 3.3 Hz, 1H), 6.66 (d, J = 3.3 Hz, 1H), 7.23–7.28 (m, 1H), 7.39 (t, J = 7.5 Hz, 2H), 7.47 (d, J = 0.9 Hz, 1H), 7.69 (d, J = 7.8 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 105.0, 111.7, 123.8, 127.3, 128.7, 130.9, 142.1, 154.0. Spectral data are exactly matching with the reported literature data.^29,41

2-(4-Fluorophenyl)furan

(30 mg, 73%); ¹H NMR (300 MHz, CDCl₃, δ): 6.46 (dd, J₁ = 1.8 Hz, J₂ = 3.3 Hz, 1H), 6.58 (d, J = 3.6 Hz, 1H), 7.04–7.11 (m, 2H), 7.45 (d, J = 1.2 Hz, 1H),7.60–7.66 (m, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 104.6, 111.7, 115.5, 115.8, 125.5, 125.6, 127.3, 142.0, 153.2, 160.5, 163.8. Spectral data are exactly matching with the reported literature data.⁴²

2-(4-Chlorophenyl)furan

(34 mg, 76%); ¹H NMR (300 MHz, CDCl₃, δ): 6.48 (dd, J₁ = 1.8 Hz, J₂ = 3.3 Hz, 1H), 6.64 (d, J = 3.3 Hz, 1H), 7.35 (d, J = 8.7 Hz, 2H), 7.47 (d, J = 1.2 Hz, 1H), 7.60 (d, J = 8.7 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 105.4, 111.8, 125.0, 128.9, 129.4, 133.0, 142.3, 152.9. Spectral data are exactly matching with the reported literature data.^29,41

2-(4-Bromophenyl)furan

(41 mg, 73%); ¹H NMR (300 MHz, CDCl₃ δ): 6.47 (dd, J₁ = 1.8 Hz, J₂ = 3.3 Hz, 1H), 6.66 (d, J = 3.3 Hz, 1H), 7.47–7.56 (m, 5H); ¹³C NMR (75 MHz, CDCl₃, δ): 105.6, 111.8, 121.1, 125.3, 129.8, 131.8, 142.4, 153.0. Spectral data are exactly matching with the reported literature data.^29,41

2-(4-Methoxyphenyl)furan

(31 mg, 70%); ¹H NMR (300 MHz, CDCl₃, δ): 3.83 (s, 3H), 6.45 (dd, J₁ = 1.8 Hz, J₂ = 3.3 Hz, 1H), 6.51 (d, J = 3.3 Hz, 1H), 6.92 (d, J = 9.0 Hz, 2H), 7.43 (d, J = 0.9 Hz, 1H), 7.60 (d, J = 9.0 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 55.3, 103.4, 111.5, 114.1, 124.0, 125.2, 141.4, 154.0, 159.0. Spectral data are exactly matching with the reported literature data.^29,41

2-(4-Nitrophenyl)furan

(33 mg, 70%); ¹H NMR (300 MHz, CDCl₃, δ): 6.56 (dd, J₁ = 1.8 Hz, J₂ = 3.3 Hz, 1H), 6.88 (d, J = 3.6 Hz, 1H), 7.58 (d, J = 1.5 Hz, 1H), 7.79 (d, J = 9.0 Hz, 2H), 8.25 (d, J = 9.0 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 109.0, 112.5, 123.9, 124.3, 136.4, 144.2, 146.4, 151.7. Spectral data are exactly matching the with reported literature data.^29,41

General Procedure for Arylation of Thiophene

Aryldiazonium tetrafluoroborate (0.25 mmol) was added to a stirred suspension of thiophene (1.25 mmol, 5.0 equiv) and HMF-BODIPY-loaded resin (5 mg, ∼3.6 μmol) in DMSO (2.0 mL). The reaction mixture was stirred under irradiation of green LED at 30 °C for 4 h. Then, the catalyst was separated by filtration and washed with diethyl ether for further reuse. The combined filtrate was diluted with diethyl ether, washed with water, and dried with anhydrous sodium sulfate. The solvent was removed under reduced pressure. The resulting residue was purified using column chromatography to obtain arylated thiophene in pure form.

2-(4-Nitrophenyl)thiophene

(34 mg, 67%); ¹H NMR (300 MHz, CDCl₃, δ): 7.16 (dd, J₁ = 3.9 Hz, J₂ = 5.1 Hz, 1H), 7.45 (d, J = 3.3 Hz, 1H), 7.48 (dd, J₁ = 0.9 Hz, J₂ = 3.6 Hz, 1H), 7.75 (d, J = 7.5 Hz, 2H), 8.25 (d, J = 0.9 Hz, 1H); ¹³C NMR (75 MHz, CDCl₃, δ): 124.4, 125.7, 126.0, 127.7, 128.7, 140.6, 141.6 146.6. Spectral data are exactly matching with the reported literature data.⁴³

2-(4-Chlorophenyl)thiophene

(27 mg, 55%); ¹H NMR (300 MHz, CDCl₃, δ): 7.07–7.09 (m, 1H), 7.29–7.30 (m, 1H), 7.35 (d, J = 8.4 Hz, 2H), 7.54 (d, J = 8.4 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 123.5, 125.2, 127.1, 128.1, 129.0, 133.0, 133.2, 143.1. Spectral data are exactly matching with the reported literature data.⁴³

General Procedure for Arylation of Benzene

Aryldiazonium tetrafluoroborate (0.25 mmol) was added to a stirred suspension of benzene (1.0 mL) and HMF-BODIPY-loaded resin (5 mg, ∼3.6 μmol) in DMSO (2.0 mL) . The reaction mixture was stirred under green LED at 30 °C for 12 h. Then, the catalyst was separated by filtration and washed with diethyl ether for further reuse. The combined filtrate was diluted with diethyl ether, washed with water, and dried with anhydrous sodium sulfate. The solvent was removed under reduced pressure. The resulting residue was purified using column chromatography to obtain arylated benzene in pure form.

4-Fluoro-1,1′-biphenyl

(13 mg, 30%); ¹H NMR (300 MHz, CDCl₃, δ): 7.13 (t, J = 8.4 Hz, 2H), 7.32–7.34 (m, 1H), 7.41–7.46 (m, 2H), 7.52–7.57 (m, 4H); ¹³C NMR (75 MHz, CDCl₃, δ): 115.5, 115.8, 127.1, 127.3, 128.7, 128.8, 128.9, 137.3, 137.4, 140.3, 160.9, 164.1. Spectral data are exactly matching with the reported literature data.⁴⁴

4-Nitro-1,1′-biphenyl

(23 mg, 46%); ¹H NMR (300 MHz, CDCl₃, δ): 7.43–7.54 (m, 3H), 7.62–7.65 (m, 2H), 7.75 (d, J = 9.0 Hz, 2H), 8.31 (d, J = 8.7 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 124.1, 127.4, 127.8, 128.9, 129.2, 138.8, 147.1, 147.6. Spectral data are exactly matching with the reported literature data.⁴³

4-Chloro-1,1′-biphenyl

(12 mg, 26%); ¹H NMR (300 MHz, CDCl₃, δ): 7.33–7.39 (m, 1H), 7.42–7.47 (m, 4H), 7.51–7.57 (m, 4H); ¹³C NMR (75 MHz, CDCl₃, δ): 127.0, 127.6, 128.4, 128.91, 128.93, 133.4, 139.7, 140.0. Spectral data are exactly matching with the reported literature data.⁴³

Radical Scavenger Reaction

4-Nitrobenzenediazonium tetrafluoroborate (59 mg, 0.25 mmol) was added to a stirred suspension of TEMPO (78 mg, 0.50 mmol, 2.0 equiv) and HMF-BODIPY-loaded resin (5 mg, ∼3.6 μmol) in DMSO (2.0 mL). The reaction mixture was stirred under green LED at 30 °C for 2 h. Then, the catalyst was separated by filtration and washed with diethyl ether. The combined filtrate was diluted with diethyl ether, washed with water, and dried with anhydrous sodium sulfate. The solvent was removed under reduced pressure. The resulting residue was purified using column chromatography to obtain 2,2,6,6-tetramethyl-1-(4-nitrophenoxy)piperidine in pure form.

2,2,6,6-Tetramethyl-1-(4-nitrophenoxy)piperidine

(56 mg, 80%); ¹H NMR (300 MHz, CDCl₃, δ): 0.99 (s, 6H), 1.25 (s, 6H), 1.43–1.46 (m, 1H), 1.58–1.66 (m, 5H), 7.31–7.34 (m, 2H), 8.15 (d, J = 9.3 Hz, 2H); ¹³C NMR (75 MHz, CDCl₃, δ): 16.9, 20.5, 32.3, 39.7, 60.9, 114.2, 125.6, 141.1, 168.7. Spectral data are exactly matching with the reported literature data.^29,41

General Procedure for Catalyst Recyclability

4-Chlorobenzenediazonium tetrafluoroborate (57 mg, 0.25 mmol) was added to a stirred suspension of furan (1.0 mL) in DMSO (2.0 mL) and HMF-BODIPY-loaded resin (5 mg, ∼3.6 μmol). The reaction mixture was stirred under green LED at 30 °C for 2 h. Then, the catalyst was separated by filtration and washed with diethyl ether for further reuse. The combined filtrate was diluted with diethyl ether, washed with water, and dried with anhydrous sodium sulfate. The solvent was removed under reduced pressure. The resulting residue was purified using column chromatography to obtain 2-(4-chlorophenyl)furan in pure form.

General Procedure for in Situ Diazotization and Photoarylation

t-Butyl nitrite (57 μL, 0.50 mmol) was added to a stirred suspension of furan (1.0 mL), substituted aniline (0.25 mmol), and BODIPY-loaded resin (5 mg, ∼3.6 μmol) in CH₂Cl₂ (2.0 mL). The reaction mixture was stirred under irradiation of green LED at 30 °C for 2 h. Then, the catalyst was separated by filtration and washed with diethyl ether. The combined filtrate was diluted with diethyl ether, washed with water, and dried with anhydrous sodium sulfate. The solvent was removed under reduced pressure. The resulting residue was purified using column chromatography to obtain arylated furan in pure form.

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.9b01407.

• MALDI mass spectra, ¹H NMR spectra, and ¹³C NMR spectra (PDF)

The authors declare no competing financial interest.