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Article

Palladium-Catalyzed Esterification of Aryl Fluorosulfates with Aryl Formates

by
Xue Chen
1,
Yuan Liang
1,
Wen-Wen Wang
1,
Chengping Miao
2,
Xue-Qiang Chu
1,
Weidong Rao
3,
Hao Xu
1,*,
Xiaocong Zhou
1,2,* and
Zhi-Liang Shen
1,*
1
Technical Institute of Fluorochemistry (TIF), School of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing 211816, China
2
College of Biological, Chemical Science and Engineering, Jiaxing University, 118 Jiahang Road, Jiaxing 314001, China
3
Jiangsu Provincial Key Lab for the Chemistry and Utilization of Agro-Forest Biomass, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037, China
*
Authors to whom correspondence should be addressed.
Molecules 2024, 29(9), 1991; https://doi.org/10.3390/molecules29091991
Submission received: 27 March 2024 / Revised: 20 April 2024 / Accepted: 23 April 2024 / Published: 26 April 2024
(This article belongs to the Section Organic Chemistry)
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Abstract

:
An efficient palladium-catalyzed carbonylation of aryl fluorosulfates with aryl formates for the facile synthesis of esters was developed. The cross-coupling reactions proceeded effectively in the presence of a palladium catalyst, phosphine ligand, and triethylamine in DMF to produce the corresponding esters in moderate to good yields. Of note, functionalities or substituents, such as nitro, cyano, methoxycarbonyl, trifluoromethyl, methylsulfonyl, trifluoromethoxy, fluoro, chloro, bromo, methyl, methoxy, N,N-dimethyl, and [1,3]dioxolyl, were well-tolerated in the reactions, which could be kept for late-stage modification. The reactions employing readily available and relatively robust aryl fluorosulfates as coupling electrophiles could potentially serve as an attractive alternative to traditional cross-couplings with the use of aryl halides and pseudohalides as substrates.

Graphical Abstract

1. Introduction

Esters not only widely exist in natural products, biologically/medicinally active molecules, and functional materials, but also serve as versatile and pivotal building blocks in organic synthesis [1,2,3,4]. In spite of many methods that have been well-developed for ester synthesis [1,2,3,4], the transition metal-catalyzed carbonylation has also been demonstrated to be a powerful platform for the construction of esters [5,6,7,8,9,10,11,12]. Among the various well-established carbonylative reactions, the use of formates as surrogates for toxic, flammable, and difficult-to-handle CO gas has also been proven to be an efficient and attractive approach for ester preparations [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47]. For instance, the groups of Manabe, Wu, and others reported that palladium could efficiently catalyze the cross-coupling of organohalides with formates for entry to esters (Scheme 1a) [16,17,18,19,20,21,22,23,24,25,26,27,28]. In recent decades, developing alternative electrophiles as surrogates for conventional organohalides in carbonylation have also attracted much attention from the synthetic community. In this regard, in 2022, the Zhao group reported that aryl thianthrenium salt served as efficient electrophile to participate in palladium-catalyzed carbonylation with formates for the synthesis of esters (Scheme 1b) [47].
Apart from the above-mentioned coupling electrophiles (e.g., aryl halides and thianthrenium salt), aryl fluorosulfates as readily available and shelf-stable reagents have been demonstrated to be efficient electrophiles for undergoing a wide variety of organic transformations [48,49,50,51,52,53,54,55,56,57,58,59,60]. Generally, aryl fluorosulfates could be conveniently synthesized from the reactions of phenols with very cheap SO2F2 under weakly basic conditions (using Et3N as a base) with almost quantitative yields, and they showed higher reactivity than the corresponding aryl triflates, mesylates, and tosylates, serving as an attractive alternative to conventional aryl halides and pseudohalides [48,49]. Although several cases with the use of aryl fluorosulfates as substrates for palladium-catalyzed carbonylation have been developed, in most cases, dangerous CO gas was employed as a carbonyl source [61,62,63,64,65,66]. Thus, the development of an alternative method for the carbonylation of aryl fluorosulfate is still highly demanded. In the continuation of our efforts in developing efficient organic reactions with the use of alternative electrophiles [67,68,69,70,71,72,73,74,75,76,77,78,79], herein we report a palladium-catalyzed carbonylation of aryl fluorosulfate with aryl formate for the efficient access to ester (Scheme 1c).

2. Results

Our investigation began with the optimization of reaction conditions by using phenyl sulfurofluoridate (1a) and phenyl formate (2a) as substrates (Table 1). Initially, the model reaction was performed by employing various transition metal salts as a catalyst in the presence of 1,3-bis(diphenylphosphino)propane (dppp) and Et3N in DMF at 80 °C for 12 h. Among the different catalysts (including Fe(III), Co(II), Mn(III), Cr(III), Ni(II), and Pd(II)) screened (entries 1–6), Pd(acac)2 was found to be the catalyst of choice, leading to the corresponding ester 3a in 73% NMR yield (entry 6). A subsequent survey of other palladium catalysts (entries 7–11) showed that the NMR yield of product 3a could be slightly improved to 75% by using either Pd2(dba)3 or Pd(OAc)2 as a catalyst (entries 10–11). To further improve the reaction efficiency, a variety of ligands, bases, and solvents were investigated by utilizing Pd(OAc)2 as a catalyst (see Tables S1–S3 in the Supporting Materials for details). It was observed that the use of 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (XantPhos) to replace dppp as a ligand could deliver the desired product 3a in 82% NMR yield (84% isolated yield, entry 12; also see entry 13 in Table S1). Evaluation of reaction temperatures showed that comparable yields could be obtained by performing the reactions at 60 °C or 100 °C (entries 13–14), while conducting the reaction at room temperature resulted in considerably eroded efficiency (entry 15). In addition, of the various bases and solvents examined, Et3N and DMF were found to be the optimal base and solvent for the present organic transformation (see Tables S2 and S3). Finally, control experiments (entries 16–18) indicated that palladium catalyst, base, and ligand were all essential for the efficient progress of the coupling reactions; without any of them, no expected reaction occurred.
With the establishment of the optimal reaction conditions for the coupling reactions (Table 1, entry 12), we proceeded to examine substrate scope of the reaction by employing a range of structurally diverse aryl fluorosulfates. As illustrated in Figure 1, aryl fluorosulfates 1b–n possessing either electron-withdrawing group or electron-donating substituent in the aryl ring efficiently underwent the cross-coupling with phenyl formate (2a) to produce the anticipated ester 3b–n in 24–88% yields. In addition, naphthyl-substituted fluorosulfate 1o worked equally well with 2a under established conditions to give the product 3o in 72% yield. Moreover, fluorosulfate 1p derived from pyridine was proven to be a suitable candidate for the current esterification, providing the desired product 3p in 72% yield. Notably, functional groups or substituents, including nitro, cyano, methylsulfonyl, trifluoromethoxy, fluoro, chloro, t-butyl, phenyl, methyl, methoxy, N,N-dimethyl, and [1,3]dioxolyl, were well-tolerated in the reaction, which could be retained for downstream derivatization. However, when sterically congested 2,6-dimethyl phenyl fluorosulfate was employed as a coupling partner, none of the desired cross-coupled product was obtained, presumably because of the inherent steric hindrance in the substrate.
Next, substrate scope with respect to aryl formates was studied (Figure 2). It was found that aryl formates 2b–n derived from either an electron-poor or electron-rich phenyl ring were capable of efficiently taking part in the coupling reaction with phenyl sulfurofluoridate (1a), leading to the corresponding esters 4b–n in modest to good yields. The starting material 1g containing a relatively reactive C-Br bond could be employed as well, albeit generating the desired product 4g in 36% yield. In addition, substrates 2h–j bearing a methyl group at the ortho, meta, and para position of phenyl ring could react in a similar manner. Likewise, a plethora of functionalities, such as COOMe, CF3, OCF3, F, Cl, Br, Me, tBu, Ph, OMe, and OPh, were well-amenable to the reaction. Moreover, naphthyl- and pyrenyl-substituted formates 2o–q made good substrates as well, providing the anticipated esters 4o–q in 78–80% yields. However, when heteroaryl formate 2r derived from quinoline was subjected to cross-coupling with phenyl sulfurofluoridate (1a) under the optimized reaction conditions, none of expected product 4r was obtained.
The synthetic utility of the present coupling reaction was further demonstrated in the functionalization of substrates derived from naturally occurring molecules. As shown in Figure 3, the carbonylation could be applied to fluorosulfates 1q–r and/or formate 2s derived from estrone and pterostilbene under the developed conditions, producing the products 3q–r and 4s in 29–92% yields.
Finally, the current palladium-catalyzed carbonylation of aryl fluorosulfates with aryl formates was found to be amenable to gram-scale synthesis. As shown in Scheme 2, the 6 mmol-scale reaction using 1.06 g of aryl fluorosulfates 1a as substrate proceeded equally well under well-established conditions to give the product 3a in 78% yield.
Based on previous reports [16,17,18,19,20,21,22,23,24,25,26,27,28], a possible reaction mechanism was proposed (Figure 4). Initially, active zero-valent palladium species (LnPd0) A, which is in situ generated in the reaction system, inserts into aryl fluorosulfate 1 to give an arylpalladium(II) intermediate B. On the other hand, carbon monoxide (CO) and phenol (Ar2OH) are in situ produced from aryl formate 2 under the action of Et3N. Next, the insertion of CO into organopalladium B gives an acylpalladium(II) species C, which undergoes exchange with phenol (Ar2OH) to obtain the corresponding phenoxy(acyl)palladium intermediate D. Finally, a reductive elimination of intermediate D occurs to furnish the desired product 3-4, along with the re-production of palladium species A, which enters the next catalytic cycle.

3. Materials and Methods

3.1. General Information

Unless otherwise stated, all reagents were purchased from commercial suppliers and used without further purification. All the aryl fluorosulfates 1 and aryl formates 2 were prepared by following reported method [40,73,80]. Analytical thin layer chromatography (TLC) was performed using silica gel plate (0.2 mm thickness). Subsequent to elution, plates were visualized using UV radiation (254 nm). Flash chromatography was performed using Merck silica gel (200–300 mesh) for column chromatography with freshly distilled solvents. IR spectra were recorded on a FT-IR spectrophotometer using KBr optics. 1H, 13C, and 19F NMR spectra were recorded in CDCl3 on Bruker Avance or Jeol 400 MHz spectrometers. Tetramethylsilane (TMS) served as internal standard for 1H, 13C and 19F NMR analysis. High resolution mass spectra (HRMS) were obtained on a Waters Q-TOF Premier Spectrometer (ESI source).

3.2. Experimental

3.2.1. General Procedure for the Synthesis of Aryl Fluorosulfates 1a–r

A 500 mL single-neck round-bottom flask was sequentially charged with phenol (100 mmol, 1.0 equiv.), dichloromethane (250 mL, 0.4 M), and triethylamine (42 mL, 300 mmol, 3.0 equiv.), and it was then sealed with a rubber septum. The atmosphere above the solution was removed by gentle vacuum, and SO2F2 gas was subsequently introduced into the flask by a needle from a balloon filled with SO2F2 gas. The reaction mixture was vigorously stirred at room temperature for 12 h. The solvent was evaporated, and the residual was purified by silica gel column chromatography using petroleum ether and EtOAc as eluent to obtain the pure product of aryl fluorosulfate. Spectral data of these compounds are in accordance with those previously documented [73,80].

3.2.2. General Procedure for the Synthesis of Aryl Formates 2a–s

Formic acid (2.3 mL, 60 mmol, 6.0 equiv.) was added to acetic anhydride (3.8 mL, 40 mmol, 4.0 equiv.) at room temperature. The mixture was stirred at 60 °C (oil bath) for 4 h and cooled to room temperature. The resulting solution was transferred to a 100 mL single-neck round-bottom flask containing phenol (10 mmol, 1.0 equiv.) and NaOAc (0.82 g, 10 mmol, 1.0 equiv.). The mixture was stirred at room temperature for 4 h. Then, CH2Cl2 and water was added to the mixture and the organic layer was extracted with CH2Cl2 (60 mL × 3), washed with saturated NaHCO3 solution and brine, and dried over anhydrous Na2SO4. The extracts were concentrated under reduced pressure to obtain the crude product, which was further purified through silica gel column chromatography using petroleum ether and EtOAc as eluent to obtain the pure product of aryl formate. Aryl formates 2a–r are known compounds, and their characterization data are in accord with the reported ones [40,47]. Aryl formate 2s is a new compound, and its characterization data are shown below.

3.2.3. General Procedure for the Cross-Coupling of Aryl Fluorosulfates with Aryl Formates

An oven-dried sealed tube containing a stirring bar was charged with Pd(OAc)2 (5.6 mg, 0.025 mmol, 5 mol%) and XantPhos (14.5 mg, 0.025 mmol, 5 mol%). The sealed tube was then evacuated and backfilled with nitrogen gas three times. The anhydrous DMF (2 mL), aryl fluorosulfate 1 (0.5 mmol, 1 equiv.), aryl formate 2 (1.0 mmol, 2 equiv.), and Et3N (101.2 mg, 1.0 mmol, 2 equiv.) were then added under nitrogen atmosphere. The reaction mixture was stirred at 80 °C (oil bath) for 12 h before quenching with saturated NH4Cl solution (10 mL) and extracting with EtOAc (20 mL × 3). The organic layers were combined, washed with saturated brine, and dried over Na2SO4. The extracts were concentrated under reduced pressure to obtain the crude product, which was further purified through silica gel column chromatography (using EtOAc/petroleum ether as eluents) to yield the products 3-4.

3.2.4. Gram-Scale Synthesis of Aryl Fluorosulfate 1a with Aryl Formate 2a

An oven-dried sealed tube containing a stirring bar was charged with Pd(OAc)2 (67.4 mg, 0.3 mmol, 5 mol%) and XantPhos (173.6 mg, 0.3 mmol, 5 mol%). The sealed tube was then evacuated and backfilled with nitrogen gas three times. The anhydrous DMF (10 mL), aryl fluorosulfate 1a (1057.0 mg, 6 mmol, 1 equiv.), aryl formate 2a (1465.4 mg, 12 mmol, 2 equiv.), and Et3N (1214.3 mg, 12 mmol, 2 equiv.) were then added under nitrogen atmosphere. The reaction mixture was stirred at 80 °C (oil bath) for 12 h before quenching with saturated NH4Cl solution (20 mL) and extracting with EtOAc (60 mL × 3). The organic layers were combined, washed with brine, and dried over Na2SO4. The extracts were concentrated under reduced pressure to obtain the crude product, which was further purified through silica gel column chromatography (using EtOAc/petroleum ether as eluents) to yield the product 3a in 78% yield (931.5 mg).
(E)-4-(3,5-Dimethoxystyryl)phenyl formate (2r). Yield = 98%, 2.79 g (10 mmol scale). White solid. 1H NMR (400 MHz, CDCl3): δ 8.32 (s, 1H), 7.58–7.49 (m, 2H), 7.17–6.96 (m, 4H), 6.67 (d, J = 2.3 Hz, 2H), 6.42 (t, J = 2.3 Hz, 1H), 3.83 (s, 6H) ppm. 13C NMR (100 MHz, CDCl3): δ 160.9, 159.2, 149.1, 138.9, 135.4, 129.2, 127.8, 127.6, 121.3, 104.5, 100.0, 55.3 ppm. IR (KBr, neat): ν = 3084, 1502, 1267, 1224, 1174, 977, 853, 670 cm−1. HRMS (ESI, m/z): calcd for C17H17O4+ [M+H]+ 285.1121, found: 285.1122.
Phenyl benzoate (3a). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 84%, 83.3 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.29–8.23 (m, 2H), 7.70–7.64 (m, 1H), 7.55 (dd, J = 8.4, 7.0 Hz, 2H), 7.51–7.44 (m, 2H), 7.35–7.24 (m, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.1, 150.8, 133.5, 130.1, 129.4 (2C), 128.5, 125.8, 121.6 ppm. IR (KBr, neat): ν = 3326, 1730, 1486, 1262, 1198, 1062, 751, 704 cm−1. HRMS (ESI, m/z): calcd for C13H11O2+ [M+H]+ 199.0754, found: 199.0750. Spectral data of the product are in accordance with those previously documented [47].
Phenyl 4-nitrobenzoate (3b). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 50:1). Yield = 24%, 28.8 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.43–8.31 (m, 4H), 7.53–7.42 (m, 2H), 7.36–7.29 (m, 1H), 7.27–7.19 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 163.3, 150.9, 150.5, 134.9, 131.3, 129.7, 126.4, 123.7, 121.4 ppm. IR (KBr, neat): ν = 3338, 2855, 1742, 1528, 1269, 1184, 1079, 711 cm−1. HRMS (ESI, m/z): calcd for C13H10NO4+ [M+H]+ 244.0604, found: 244.0604. Spectral data of the product are in accordance with those previously documented [81].
Phenyl 4-cyanobenzoate (3c). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 50:1). Yield = 88%, 98.2 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.12–8.06 (m, 2H), 7.62–7.56 (m, 2H), 7.28–7.20 (m, 2H), 7.12–7.06 (m, 1H), 7.03–6.98 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 163.5, 150.4, 133.2, 132.3, 130.5, 129.6, 126.2, 121.3, 117.8, 116.8 ppm. IR (KBr, neat): ν = 3320, 2233, 1740, 1483, 1268, 864, 763, 688 cm−1. HRMS (ESI, m/z): calcd for C14H10NO2+ [M+H]+ 224.0706, found: 224.0702. Spectral data of the product are in accordance with those previously documented [81].
Phenyl 4-(methylsulfonyl)benzoate (3d). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 10:1). Yield = 64%, 88.8 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.43–8.38 (m, 2H), 8.13–8.08 (m, 2H), 7.49–7.43 (m, 2H), 7.34–7.28 (m, 1H), 7.25–7.20 (m, 2H), 3.11 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 163.6, 150.5, 144.8, 134.3, 131.1, 129.6, 127.7, 126.3, 121.4, 44.3 ppm. IR (KBr, neat): ν = 3054, 1732, 1280, 1216, 1079, 829, 742, 689 cm−1. HRMS (ESI, m/z): calcd for C14H13O4S+ [M+H]+ 277.0529, found: 277.0528. Spectral data of the product are in accordance with those previously documented [82].
Phenyl 4-(trifluoromethoxy)benzoate (3e). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 76%, 106.7 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.30–8.23 (m, 2H), 7.49–7.41 (m, 2H), 7.38–7.27 (m, 3H), 7.25–7.18 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.0, 153.0, 150.6, 132.2, 129.6, 127.8, 126.1, 121.6, 120.4, 120.2 (q, J = 257.9 Hz) ppm. 19F NMR (376 MHz, CDCl3): δ -57.45 (s, 3F) ppm. IR (KBr, neat): ν = 3326, 1735, 1505, 1264, 1073, 918, 765, 691 cm−1. HRMS (ESI, m/z): calcd for C14H10F3O3+ [M+H]+ 283.0577, found: 283.0575. Spectral data of the product are in accordance with those previously documented [83].
Phenyl 4-fluorobenzoate (3f). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 88%, 95.5 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.27–8.19 (m, 2H), 7.47–7.41 (m, 2H), 7.32–7.26 (m, 1H), 7.25–7.14 (m, 4H) ppm. 13C NMR (100 MHz, CDCl3): δ 166.1 (d, J = 255.1 Hz), 164.2, 150.8, 132.8 (d, J = 9.4 Hz), 129.5, 126.0, 125.8 (d, J = 2.8 Hz), 121.6, 115.8 (d, J = 22.1 Hz) ppm. 19F NMR (376 MHz, CDCl3): δ -104.30 (s, 1F) ppm. IR (KBr, neat): ν = 3331, 2921, 1733, 1596, 1506, 1278, 745, 687 cm−1. HRMS (ESI, m/z): calcd for C13H10FO2+ [M+H]+ 217.0659, found: 217.0658. Spectral data of the product are in accordance with those previously documented [81].
Phenyl 4-chlorobenzoate (3g). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 32%, 37.6 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.21–8.14 (m, 2H), 7.54–7.43 (m, 4H), 7.35–7.29 (m, 1H), 7.26–7.21 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.3, 150.6, 140.0, 131.5, 129.5, 128.9, 127.9, 126.0, 121.6 ppm. IR (KBr, neat): ν = 3325, 2696, 1731, 1591, 1280, 1075, 852, 754 cm−1. HRMS (ESI, m/z): calcd for C13H10ClO2+ [M+H]+ 233.0364, found: 233.0364. Spectral data of the product are in accordance with those previously documented [47].
Phenyl 4-(tert-butyl)benzoate (3h). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 78%, 99.2 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.19–8.15 (m, 2H), 7.58–7.53 (m, 2H), 7.48–7.42 (m, 2H), 7.31–7.26 (m, 1H), 7.25–7.21 (m, 2H), 1.39 (s, 9H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.2, 157.3, 151.0, 130.0, 129.4, 126.7, 125.7, 125.5, 121.7, 35.2, 31.1 ppm. IR (KBr, neat): ν = 3332, 3055, 2958, 1732, 1267, 1185, 1073, 750 cm−1. HRMS (ESI, m/z): calcd for C17H19O2+ [M+H]+ 255.1380, found: 255.1379. Spectral data of the product are in accordance with those previously documented [47].
Phenyl [1,1’-biphenyl]-4-carboxylate (3i). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 82%, 112.2 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.31–8.25 (m, 2H), 7.77–7.72 (m, 2H), 7.69–7.64 (m, 2H), 7.53–7.40 (m, 5H), 7.32–7.27 (m, 1H), 7.26–7.22 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.1, 151.0, 146.3, 139.8, 130.7, 129.5, 129.0, 128.3, 128.2, 127.3, 127.2, 125.9, 121.7 ppm. IR (KBr, neat): ν = 3326, 2852, 1730, 1605, 1265, 1082, 857, 696 cm−1. HRMS (ESI, m/z): calcd for C19H15O2+ [M+H]+ 275.1067, found: 275.1069. Spectral data of the product are in accordance with those previously documented [47].
Phenyl 3,5-dimethylbenzoate (3j). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 85%, 96.0 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 7.85 (s, 2H), 7.48–7.42 (m, 2H), 7.32–7.26 (m, 2H), 7.25–7.20 (m, 2H), 2.42 (s, 6H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.5, 151.0, 138.2, 135.2, 129.4, 129.3, 127.8, 125.8, 121.7, 21.1 ppm. IR (KBr, neat): ν = 3327, 2918, 1735, 1310, 1100, 896, 731, 505 cm−1. HRMS (ESI, m/z): calcd for C15H15O2+ [M+H]+ 227.1067, found: 227.1066. Spectral data of the product are in accordance with those previously documented [47].
Phenyl 4-methoxybenzoate (3k). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 48%, 54.8 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.26–8.20 (m, 2H), 7.53–7.46 (m, 2H), 7.36–7.25 (m, 3H), 7.09–7.02 (m, 2H), 3.95 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.9, 163.8, 151.0, 132.2, 129.4, 125.7, 121.79, 121.76, 113.8, 55.5 ppm. IR (KBr, neat): ν = 3328, 2930, 1726, 1607, 1510, 1164, 763, 564 cm−1. HRMS (ESI, m/z): calcd for C14H13O3+ [M+H]+ 229.0859, found: 229.0859. Spectral data of the product are in accordance with those previously documented [47].
Phenyl 3-methoxybenzoate (3l). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 65%, 73.9 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 7.83 (dt, J = 7.7, 1.2 Hz, 1H), 7.74–7.71 (m, 1H), 7.48–7.40 (m, 3H), 7.32–7.27 (m, 1H), 7.25–7.17 (m, 3H), 3.89 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.0, 159.6, 150.9, 130.8, 129.6, 129.5, 125.9, 122.5, 121.7, 120.1, 114.4, 55.5 ppm. IR (KBr, neat): ν = 3316, 3055, 2918, 1725, 1598, 1484, 1276, 741 cm−1. HRMS (ESI, m/z): calcd for C14H13O3+ [M+H]+ 229.0859, found: 229.0857. Spectral data of the product are in accordance with those previously documented [82].
Phenyl benzo[d][1,3]dioxole-5-carboxylate (3m). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 37%, 45.0 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 7.83 (dd, J = 8.2, 1.7 Hz, 1H), 7.62 (d, J = 1.7 Hz, 1H), 7.46–7.39 (m, 2H), 7.30–7.24 (m, 1H), 7.23–7.17 (m, 2H), 6.91 (d, J = 8.2 Hz, 1H), 6.08 (s, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.5, 152.2, 150.9, 147.9, 129.4, 126.2, 125.8, 123.4, 121.7, 109.9, 108.1, 101.9 ppm. IR (KBr, neat): ν = 3325, 2898, 1723, 1608, 1489, 1445, 1193, 750 cm−1. HRMS (ESI, m/z): calcd for C14H11O4+ [M+H]+ 243.0652, found: 243.0650. Spectral data of the product are in accordance with those previously documented [47].
Phenyl 3-(dimethylamino)benzoate (3n). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 10:1). Yield = 85%, 103.1 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 7.55–7.49 (m, 2H), 7.42–7.36 (m, 2H), 7.35–7.29 (m, 1H), 7.25–7.16 (m, 3H), 6.96–6.91 (m, 1H), 2.98 (s, 6H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.8, 151.1, 150.5, 130.1, 129.4, 129.1, 125.7, 121.8, 118.0, 117.3, 113.5, 40.5 ppm. IR (KBr, neat): ν = 3330, 2809, 1733, 1600, 1189, 1089, 990, 691 cm−1. HRMS (ESI, m/z): calcd for C15H16NO2+ [M+H]+ 242.1176, found: 242.1175. Spectral data of the product are in accordance with those previously documented [82].
Phenyl 2-naphthoate (3o). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 72%, 88.9 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.83–8.78 (m, 1H), 8.26–8.18 (m, 1H), 8.06–7.90 (m, 3H), 7.69–7.55 (m, 2H), 7.50–7.44 (m, 2H), 7.34–7.27 (m, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.3, 151.0, 135.8, 132.4, 131.9, 129.5, 129.4, 128.6, 128.4, 127.8, 126.8, 126.7, 125.9, 125.4, 121.7 ppm. IR (KBr, neat): ν = 3054, 1732, 1591, 1486, 1280, 829, 742, 689 cm−1. HRMS (ESI, m/z): calcd for C17H13O2+ [M+H]+ 249.0910, found: 249.0913. Spectral data of the product are in accordance with those previously documented [81].
Phenyl nicotinate (3p). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 10:1). Yield = 72%, 71.3 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 9.22 (dd, J = 2.2, 0.9 Hz, 1H), 8.67 (dd, J = 4.9, 1.8 Hz, 1H), 8.27 (dt, J = 8.0, 2.0 Hz, 1H), 7.31–7.24 (m, 3H), 7.14–7.09 (m, 1H), 7.07–7.02 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 163.8, 154.0, 151.3, 150.4, 137.5, 129.6, 126.2, 125.5, 123.4, 121.5 ppm. IR (KBr, neat): ν = 3042, 1740, 1589, 1490, 1428, 1277, 732, 707 cm−1. HRMS (ESI, m/z): calcd for C12H10NO2+ [M+H]+ 200.0706, found: 200.0704. Spectral data of the product are in accordance with those previously documented [83].
Phenyl (8R,9S,13S,14S)-13-methyl-17-oxo-7,8,9,11,12,13,14,15,16,17-decahydro-6H-cyclopenta[a]phenanthrene-3-carboxylate (3q). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 50:1). Yield = 72%, 135.2 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.00–7.93 (m, 2H), 7.46–7.39 (m, 3H), 7.30–7.24 (m, 1H), 7.23–7.17 (m, 2H), 3.05–2.96 (m, 2H), 2.58–2.43 (m, 2H), 2.37 (td, J = 10.9, 4.1 Hz, 1H), 2.23–1.97 (m, 4H), 1.72–1.45 (m, 6H), 0.93 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 220.5, 165.2, 150.9, 145.9, 136.9, 130.7, 129.4, 127.4, 126.8, 125.7, 125.6, 121.6, 50.4, 47.8, 44.6, 37.7, 35.7, 31.4, 29.1, 26.1, 25.5, 21.5, 13.7 ppm. IR (KBr, neat): ν = 3446, 3044, 2939, 1717, 1568, 1493, 739, 505 cm−1. HRMS (ESI, m/z): calcd for C25H27O3+ [M+H]+ 375.1955, found: 375.1957.
Phenyl (E)-4-(3,5-dimethoxystyryl)benzoate (3r). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 29%, 51.8 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.22–8.16 (m, 2H), 7.66–7.60 (m, 2H), 7.49–7.40 (m, 3H), 7.25–7.14 (m, 4H), 6.71 (d, J = 2.3 Hz, 2H), 6.45 (t, J = 2.2 Hz, 1H), 3.85 (s, 6H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.0, 161.0, 150.9, 142.3, 138.6, 131.6, 130.6, 129.5, 128.3, 127.9, 126.5, 125.9, 121.7, 104.8, 100.6, 55.4 ppm. IR (KBr, neat): ν = 3529, 3314, 2918, 1735, 1592, 1310, 1194, 689 cm−1. HRMS (ESI, m/z): calcd for C23H21O4+ [M+H]+ 361.1434, found: 361.1435.
Methyl 4-(benzoyloxy)benzoate (4b). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 50:1). Yield = 82%, 105.7 mg. Colorless oil. 1H NMR (400 MHz, CDCl3): δ 8.22–8.18 (m, 2H), 8.14–8.10 (m, 2H), 7.67–7.61 (m, 1H), 7.54–7.48 (m, 2H), 7.33–7.28 (m, 2H), 3.92 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 166.3, 164.5, 154.5, 133.8, 131.1, 130.2, 129.0, 128.6, 127.7, 121.7, 52.1 ppm. IR (KBr, neat): ν = 3320, 2956, 1723, 1602, 1440, 1266, 761, 698 cm−1. HRMS (ESI, m/z): calcd for C15H13O4 + [M+H]+ 257.0808, found: 257.0805. Spectral data of the product are in accordance with those previously documented [81].
4-(Trifluoromethyl)phenyl benzoate (4c). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 82%, 108.5 mg. Colorless oil. 1H NMR (400 MHz, CDCl3): δ 8.26–8.19 (m, 2H), 7.75–7.64 (m, 3H), 7.57–7.51 (m, 2H), 7.40–7.34 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.6, 153.4 (q, J = 1.9 Hz), 133.9, 130.2, 128.9, 128.7, 128.4 (q, J = 32.5 Hz), 126.8 (q, J = 3.9 Hz), 125.1 (q, J = 260.0 Hz), 122.2 ppm. 19F NMR (376 MHz, CDCl3): δ -62.05 (s, 3F) ppm. IR (KBr, neat): ν = 3325, 2851, 1732, 1453, 1118, 882, 704, 593 cm−1. HRMS (ESI, m/z): calcd for C14H10F3O2+ [M+H]+ 267.0627, found: 267.0626. Spectral data of the product are in accordance with those previously documented [81].
4-(Trifluoromethoxy)phenyl benzoate (4d). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 63%, 88.2 mg. Colorless oil. 1H NMR (400 MHz, CDCl3): δ 8.22–8.17 (m, 2H), 7.67–7.62 (m, 1H), 7.55–7.49 (m, 2H), 7.31–7.23 (m, 4H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.9, 149.2, 146.6, 133.8, 130.2, 129.1, 128.6, 123.0, 122.2, 120.4 (q, J = 255.9 Hz) ppm. 19F NMR (376 MHz, CDCl3): δ -57.99 (s, 3F) ppm. IR (KBr, neat): ν = 3066, 2921, 1910, 1731, 1508, 1154, 705, 535 cm−1. HRMS (ESI, m/z): calcd for C14H10F3O3+ [M+H]+ 283.0577, found: 283.0574. Spectral data of the product are in accordance with those previously documented [84].
4-Fluorophenyl benzoate (4e). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 71%, 77.0 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.23–8.17 (m, 2H), 7.69–7.62 (m, 1H), 7.56–7.50 (m, 2H), 7.22–7.16 (m, 2H), 7.16–7.08 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.2, 160.3 (d, J = 244.2 Hz), 146.7 (d, J = 2.8 Hz), 133.7, 130.1, 129.2, 128.6, 123.1 (d, J = 8.5 Hz), 116.1 (d, J = 23.5 Hz) ppm. 19F NMR (376 MHz, CDCl3): δ -116.80 (s, 1F) ppm. IR (KBr, neat): ν = 3326, 2359, 1732, 1504, 1188, 1063, 706, 526 cm−1. HRMS (ESI, m/z): calcd for C13H10FO2+ [M+H]+ 217.0659, found: 217.0659. Spectral data of the product are in accordance with those previously documented [83].
4-Chlorophenyl benzoate (4f). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 73%, 84.9 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.23–8.18 (m, 2H), 7.72–7.61 (m, 1H), 7.58–7.48 (m, 2H), 7.44–7.36 (m, 2H), 7.23–7.14 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.9, 149.3, 133.8, 131.2, 130.1, 129.5, 129.1, 128.6, 123.1 ppm. IR (KBr, neat): ν = 3062, 1732, 1488, 1266, 1060, 876, 705, 513 cm−1. HRMS (ESI, m/z): calcd for C13H10ClO2+ [M+H]+ 233.0364, found: 233.0361. Spectral data of the product are in accordance with those previously documented [81].
4-Bromophenyl benzoate (4g). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 36%, 50.3 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.22–8.16 (m, 2H), 7.69–7.62 (m, 1H), 7.58–7.49 (m, 4H), 7.15–7.09 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.9, 149.9, 133.8, 132.5, 130.2, 129.1, 128.6, 123.5, 119.0 ppm. IR (KBr, neat): ν = 3333, 2849, 1732, 1486, 1280, 1059, 805, 510 cm−1. HRMS (ESI, m/z): calcd for C13H10BrO2+ [M+H]+ 276.9859, found: 276.9862. Spectral data of the product are in accordance with those previously documented [83].
p-Tolyl benzoate (4h). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 70%, 73.8 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.24–8.20 (m, 2H), 7.68–7.61 (m, 1H), 7.56–7.49 (m, 2H), 7.26–7.21 (m, 2H), 7.14–7.08 (m, 2H), 2.39 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.4, 148.6, 135.5, 133.5, 130.1, 130.0, 129.6, 128.5, 121.3, 20.9 ppm. IR (KBr, neat): ν = 3328, 2920, 1727, 1597, 1508, 1270, 706, 511 cm−1. HRMS (ESI, m/z): calcd for C14H13O2+ [M+H]+ 213.0910, found: 213.0907. Spectral data of the product are in accordance with those previously documented [81].
m-Tolyl benzoate (4i). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 62%, 65.6 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.25–8.22 (m, 2H), 7.68–7.62 (m, 1H), 7.56–7.50 (m, 2H), 7.34 (t, J = 7.7 Hz, 1H), 7.13–7.02 (m, 3H), 2.41 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.3, 150.8, 139.6, 133.5, 130.1, 129.6, 129.2, 128.5, 126.7, 122.3, 118.6, 21.3 ppm. IR (KBr, neat): ν = 3325, 2921, 1735, 1487, 1237, 1145, 1064, 707 cm−1. HRMS (ESI, m/z): calcd for C14H13O2+ [M+H]+ 213.0910, found: 213.0910. Spectral data of the product are in accordance with those previously documented [85].
o-Tolyl benzoate (4j). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 71%, 74.9 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.28 (dt, J = 8.5, 1.6 Hz, 2H), 7.70–7.65 (m, 1H), 7.58–7.53 (m, 2H), 7.34–7.27 (m, 2H), 7.25–7.16 (m, 2H), 2.28 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 164.8, 149.5, 133.5, 131.1, 130.2, 130.1, 129.4, 128.6, 126.9, 126.0, 121.9, 16.2 ppm. IR (KBr, neat): ν = 2927, 1735, 1491, 1266, 1111, 1024, 748, 706 cm−1. HRMS (ESI, m/z): calcd for C14H13O2+ [M+H]+ 213.0910, found: 213.0910. Spectral data of the product are in accordance with those previously documented [85].
4-(tert-Butyl)phenyl benzoate (4k). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 83%, 105.3 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.26–8.21 (m, 2H), 7.68–7.62 (m, 1H), 7.53 (ddt, J = 8.1, 6.6, 1.0 Hz, 2H), 7.49–7.44 (m, 2H), 7.19–7.14 (m, 2H), 1.36 (s, 9H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.3, 148.6, 148.5, 133.5, 130.1, 129.6, 128.5, 126.4, 120.9, 34.5, 31.4 ppm. IR (KBr, neat): ν = 3057, 2963, 1732, 1598, 1508, 1262, 707, 552 cm−1. HRMS (ESI, m/z): calcd for C17H19O2+ [M+H]+ 255.1380, found: 255.1382. Spectral data of the product are in accordance with those previously documented [85].
[1,1’-Biphenyl]-4-yl benzoate (4l). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 79%, 108.7 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.28–8.24 (m, 2H), 7.70–7.65 (m, 3H), 7.65–7.61 (m, 2H), 7.58–7.52 (m, 2H), 7.51–7.45 (m, 2H), 7.41–7.36 (m, 1H), 7.35–7.30 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.2, 150.3, 140.4, 139.0, 133.6, 130.2, 129.5, 128.8, 128.6, 128.2 127.3, 127.1, 122.0 ppm. IR (KBr, neat): ν = 3325, 2923, 1731, 1598, 1486, 1280, 758, 703 cm−1. HRMS (ESI, m/z): calcd for C19H15O2+ [M+H]+ 275.1067, found: 275.1068. Spectral data of the product are in accordance with those previously documented [81].
4-Methoxyphenyl benzoate (4m). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 52%, 59.0 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.23–8.19 (m, 2H), 7.66–7.61 (m, 1H), 7.54–7.48 (m, 2H), 7.17–7.11 (m, 2H), 6.97–6.92 (m, 2H), 3.83 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.5, 157.3, 144.4, 133.5, 130.1, 129.6, 128.5, 122.4, 114.5, 55.6 ppm. IR (KBr, neat): ν = 3323, 2837, 1724, 1506, 1247, 1192, 1025, 814 cm−1. HRMS (ESI, m/z): calcd for C14H13O3+ [M+H]+ 229.0859, found: 229.0862. Spectral data of the product are in accordance with those previously documented [81].
4-Phenoxyphenyl benzoate (4n). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 44%, 63.7 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.26–8.19 (m, 2H), 7.70–7.61 (m, 1H), 7.57–7.48 (m, 2H), 7.41–7.32 (m, 2H), 7.23–7.17 (m, 2H), 7.16–7.11 (m, 1H), 7.10–7.02 (m, 4H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.3, 157.2, 154.8, 146.3, 133.6, 130.1, 129.8, 129.4, 128.6, 123.4, 122.8, 119.6, 118.8 ppm. IR (KBr, neat): ν = 3332, 2734, 1732, 1588, 1500, 1188, 1065, 708 cm−1. HRMS (ESI, m/z): calcd for C19H15O3+ [M+H]+ 291.1016, found: 291.1016. Spectral data of the product are in accordance with those previously documented [83].
Naphthalen-1-yl benzoate (4o). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 79%, 98.1 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.43–8.35 (m, 2H), 8.01–7.98 (m, 1H), 7.96–7.92 (m, 1H), 7.83 (d, J = 8.3 Hz, 1H), 7.75–7.68 (m, 1H), 7.63–7.52 (m, 5H), 7.43 (dd, J = 7.5, 1.0 Hz, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.2, 146.8, 134.6, 133.7, 130.3, 129.3, 128.7, 128.0, 126.9, 126.5, 126.4, 126.0, 125.4, 121.2, 118.2 ppm. IR (KBr, neat): ν = 3060, 1740, 1598, 1451, 1254, 1021, 871, 704 cm−1. HRMS (ESI, m/z): calcd for C17H13O2+ [M+H]+ 249.0910, found: 249.0909. Spectral data of the product are in accordance with those previously documented [81].
Naphthalen-2-yl benzoate (4p). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 80%, 99.2 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.36–8.28 (m, 2H), 7.98–7.84 (m, 3H), 7.78–7.72 (m, 1H), 7.72–7.64 (m, 1H), 7.61–7.48 (m, 4H), 7.46–7.37 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.3, 148.5, 133.8, 133.6, 131.5, 130.2, 129.5, 129.4, 128.6, 127.8, 127.6, 126.6, 125.7, 121.2, 118.7 ppm. IR (KBr, neat): ν = 3328, 2921, 1729, 1451, 1238, 1062, 708, 478 cm−1. HRMS (ESI, m/z): calcd for C17H13O2+ [M+H]+ 249.0910, found: 249.0911. Spectral data of the product are in accordance with those previously documented [81].
Pyren-1-yl benzoate (4q). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 78%, 125.0 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.48–8.41 (m, 2H), 8.26–8.14 (m, 4H), 8.11–8.01 (m, 4H), 7.96–7.90 (m, 1H), 7.78–7.71 (m, 1H), 7.67–7.59 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.6, 144.5, 133.8, 131.1, 130.9, 130.4, 129.4, 129.3, 128.8, 128.2, 127.1, 126.3, 125.6, 125.5, 125.2, 125.0, 124.5, 123.3, 120.3, 119.8 ppm. IR (KBr, neat): ν = 3446, 3047, 1735, 1597, 1452, 1229, 1065, 705 cm−1. HRMS (ESI, m/z): calcd for C23H15O2+ [M+H]+ 323.1067, found: 323.1065. Spectral data of the product are in accordance with those previously documented [86].
(E)-4-(3,5-Dimethoxystyryl)phenyl benzoate (4s). This product was purified by silica gel column chromatography using petroleum ether/ethyl acetate as eluent (petroleum ether/EtOAc = 100:1). Yield = 92%, 166.5 mg. White solid. 1H NMR (400 MHz, CDCl3): δ 8.27–8.22 (m, 2H), 7.69–7.63 (m, 1H), 7.60–7.50 (m, 4H), 7.27–7.23 (m, 2H), 7.16–7.00 (m, 2H), 6.72 (d, J = 2.2 Hz, 2H), 6.45 (t, J = 2.3 Hz, 1H), 3.84 (s, 6H) ppm. 13C NMR (100 MHz, CDCl3): δ 165.0, 160.8, 150.2, 139.0, 134.8, 133.5, 130.0, 129.3, 128.7, 128.5, 128.0, 127.4, 121.8, 104.4, 99.9, 55.2 ppm. IR (KBr, neat): ν = 3327, 2832, 1727, 1591, 1455, 1152, 1065, 707 cm−1. HRMS (ESI, m/z): calcd for C23H21O4+ [M+H]+ 361.1434, found: 361.1437.

4. Conclusions

In summary, an efficient protocol for the easy entry to esters through the palladium-catalyzed esterification of aryl fluorosulfates with aryl formates was realized. The carbonylative reactions efficiently occurred with the aid of palladium catalyst, phosphine ligand, and triethylamine in DMF to provide the desired esters in modest to high yields with good tolerance to a range of functional groups and substituents embedded in the aryl ring. In addition, the reaction could not only be scaled up with good efficiency, but also be applied to the utilization of substrates derived from naturally occurring estrone and pterostilbene.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules29091991/s1, optimization of reaction conditions, and copies of the 1H NMR and 13C NMR spectra of investigated compounds are available online.

Author Contributions

Synthesis and Characterization, X.C., Y.L. and W.-W.W.; methodology and project administration, X.-Q.C.; writing—original draft preparation, and supervision, Z.-L.S.; writing—review and editing, and funding acquisition, Z.-L.S., C.M., W.R., H.X. and X.Z. All authors have read and agreed to the published version of the manuscript.

Funding

We gratefully acknowledge the financial support from National Natural Science Foundation of China (22001121) and Nanjing Tech University (Start-up Grant No. 39837118).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Conflicts of Interest

The authors declare no conflicts of interest.

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Molecules 29 01991 sch001
Scheme 1. Carbonylation using formate as CO surrogate. (a) Coupling of organohalides with formates; (b) Coupling of aryl thianthrenium salt with formates; (c) Coupling of aryl fluorosulfates with formates (this work).
Scheme 1. Carbonylation using formate as CO surrogate. (a) Coupling of organohalides with formates; (b) Coupling of aryl thianthrenium salt with formates; (c) Coupling of aryl fluorosulfates with formates (this work).
Molecules 29 01991 sch001
Molecules 29 01991 g001
Figure 1. Substrate scope study by using various aryl fluorosulfates a,b. a The reactions were performed at 80 °C for 12 h under nitrogen atmosphere by using 1b–p (0.5 mmol), 2a (1.0 mmol), Pd(OAc)2 (5 mol%), XantPhos (5 mol%), and Et3N (1.0 mmol) in anhydrous DMF (2 mL). b Isolated yield.
Figure 1. Substrate scope study by using various aryl fluorosulfates a,b. a The reactions were performed at 80 °C for 12 h under nitrogen atmosphere by using 1b–p (0.5 mmol), 2a (1.0 mmol), Pd(OAc)2 (5 mol%), XantPhos (5 mol%), and Et3N (1.0 mmol) in anhydrous DMF (2 mL). b Isolated yield.
Molecules 29 01991 g001
Molecules 29 01991 g002
Figure 2. Substrate scope study by using various aryl formates a,b. a The reactions were performed at 80 °C for 12 h under nitrogen atmosphere by using 1a (0.5 mmol), 2b–r (1.0 mmol), Pd(OAc)2 (5 mol%), XantPhos (5 mol%), and Et3N (1.0 mmol) in anhydrous DMF (2 mL). b Isolated yield.
Figure 2. Substrate scope study by using various aryl formates a,b. a The reactions were performed at 80 °C for 12 h under nitrogen atmosphere by using 1a (0.5 mmol), 2b–r (1.0 mmol), Pd(OAc)2 (5 mol%), XantPhos (5 mol%), and Et3N (1.0 mmol) in anhydrous DMF (2 mL). b Isolated yield.
Molecules 29 01991 g002
Molecules 29 01991 g003
Figure 3. Late-stage derivatization of complex molecules a,b. a The reactions were performed at 80 °C for 12 h under nitrogen atmosphere by using 1 (0.5 mmol), 2 (1.0 mmol), Pd(OAc)2 (5 mol%), XantPhos (5 mol%), and Et3N (1.0 mmol) in anhydrous DMF (2 mL). b Isolated yield.
Figure 3. Late-stage derivatization of complex molecules a,b. a The reactions were performed at 80 °C for 12 h under nitrogen atmosphere by using 1 (0.5 mmol), 2 (1.0 mmol), Pd(OAc)2 (5 mol%), XantPhos (5 mol%), and Et3N (1.0 mmol) in anhydrous DMF (2 mL). b Isolated yield.
Molecules 29 01991 g003
Molecules 29 01991 sch002
Scheme 2. Gram-scale synthesis.
Scheme 2. Gram-scale synthesis.
Molecules 29 01991 sch002
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Figure 4. Proposed reaction mechanism.
Figure 4. Proposed reaction mechanism.
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Table 1. Optimization of reaction conditions by using various catalysts a.
Table 1. Optimization of reaction conditions by using various catalysts a.
Molecules 29 01991 i001
EntryCatalystYield (%) b
1Fe(acac)30
2Co(acac)20
3Mn(acac)30
4Cr(acac)30
5Ni(acac)20
6Pd(acac)273
7PdCl239
8Pd(PPh3)2Cl228
9Pd(PPh3)467
10Pd2(dba)375
11Pd(OAc)275
12Pd(OAc)282 c (84) d
13Pd(OAc)280 e
14Pd(OAc)283 f
15Pd(OAc)221 g
16-0 c
17Pd(OAc)20 c,h
18Pd(OAc)20 i
a The reactions were performed at 80 °C for 12 h under nitrogen atmosphere by using 1a (0.5 mmol), 2a (1.0 mmol), catalyst (5 mol%), dppp (5 mol%), and Et3N (1.0 mmol) in anhydrous DMF (2 mL). b Yields were determined by NMR analysis of crude reaction mixture after work-up by using 1,4-dimethoxybenzene as an internal standard. c Using XantPhos instead of dppp as ligand. d Isolated yield. e At 60 °C. f At 100 °C. g At room temperature. h Without Et3N. i Without dppp.
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MDPI and ACS Style

Chen, X.; Liang, Y.; Wang, W.-W.; Miao, C.; Chu, X.-Q.; Rao, W.; Xu, H.; Zhou, X.; Shen, Z.-L. Palladium-Catalyzed Esterification of Aryl Fluorosulfates with Aryl Formates. Molecules 2024, 29, 1991. https://doi.org/10.3390/molecules29091991

AMA Style

Chen X, Liang Y, Wang W-W, Miao C, Chu X-Q, Rao W, Xu H, Zhou X, Shen Z-L. Palladium-Catalyzed Esterification of Aryl Fluorosulfates with Aryl Formates. Molecules. 2024; 29(9):1991. https://doi.org/10.3390/molecules29091991

Chicago/Turabian Style

Chen, Xue, Yuan Liang, Wen-Wen Wang, Chengping Miao, Xue-Qiang Chu, Weidong Rao, Hao Xu, Xiaocong Zhou, and Zhi-Liang Shen. 2024. "Palladium-Catalyzed Esterification of Aryl Fluorosulfates with Aryl Formates" Molecules 29, no. 9: 1991. https://doi.org/10.3390/molecules29091991

APA Style

Chen, X., Liang, Y., Wang, W. -W., Miao, C., Chu, X. -Q., Rao, W., Xu, H., Zhou, X., & Shen, Z. -L. (2024). Palladium-Catalyzed Esterification of Aryl Fluorosulfates with Aryl Formates. Molecules, 29(9), 1991. https://doi.org/10.3390/molecules29091991

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