PCl 3 -mediated transesterification and aminolysis of tert -butyl esters via acid chloride formation

Abstract

A PCl₃-mediated conversion of tert-butyl esters into esters and amides in one-pot under air is developed. This novel protocol is highlighted by the synthesis of skeletons of bioactive molecules and gram-scale reactions. Mechanistic studies revealed that this transformation involves the formation of an acid chloride in situ, which is followed by reactions with alcohols or amines to afford the desired products.

Keywords

acid chlorides amides esters phosphorus trichloride

Introduction

Ester and amide functionalities are ubiquitous in pharmaceuticals, natural products, agriculture, functional materials, and synthetic organic chemistry.^1–7 Traditional methods for the preparation of esters and amides involve the reactions of carboxylic acids with alcohols or amines.^5,6 However, these methods suffer from dry reaction conditions and the generation of toxic wastes. In recent years, the transesterification and aminolysis of esters have represented alternative routes for the synthesis of various esters and amides.^8–11 However, transesterification and aminolysis of esters usually require the use of transition-metal catalysts such as Pd,^12,13 Co,¹⁴ Ru,^15,16 and Au,¹⁷ excess of bases,^18,19 metal alkoxides,^10,20 carbenes,^21–23 and so on,^24–28 which are limited by high costs, low availability, and harsh reaction conditions. Moreover, there are only a few examples involving the transesterification and aminolysis of esters using the same system. Thus, the development of an efficient, low-cost, and environmentally friendly methodology for the synthesis of esters and amides is in high demand.

Phosphorus trichloride (PCl₃) is a cheap and readily available industrial chemical. Recently, we became intrigued by the fact that PCl₃ may serve as a green chlorinating reagent due to one molecule of PCl₃ having three chlorine atoms. The need for esters and amides in our ongoing research encouraged us to investigate methods for their synthesis. To the best of our knowledge, there has been no report on the reaction of PCl₃ with esters that provides the corresponding acid chlorides for further reactions, albeit there are a few examples of the conversion of tert-butyl esters into acid chlorides having been reported, some of them using a large excess of chlorinating reagents.²⁹ Herein, we report an efficient PCl₃-mediated transesterification and aminolysis of esters, providing the corresponding esters and amides in good-to-high yields (Scheme 1). Notably, when a large-scale reaction was conducted, only 2/3 equiv. of PCl₃ was required.

Scheme 1.

PCl₃-mediated transesterification and aminolysis of tert-butyl esters.

Results and discussion

We initiated our research on the transesterification of tert-butyl benzoate. As demonstrated in Table 1, tert-butyl benzoate (1a) and PCl₃ (1.0 equiv.) were stirred in CH₃CN at 80 °C for 3 h, then MeOH (5.0 equiv.) was added under N₂ to afford methyl benzoate (2a) in 83% yield (entry 1). Similarly, when the reaction was conducted in air, the product was generated in 92% yield (entry 2). Further reducing or increasing the amount of MeOH did not improve the reaction efficiency (entries 3 and 4). An 87% yield of the product was generated when the reaction temperature was lowered to 60 °C (entry 5). To our delight, when 2/3 equiv. of PCl₃ was used, a 78% yield of methyl benzoate was obtained (entry 6). We also examined the reactivity of methyl, isopropyl, and phenyl benzoate in this reaction. However, no product was detected by gas chromatography–mass spectrometry (GC-MS).

Table 1.

Optimization of the reaction conditions.^a


Entry	Conditions	Yield (%)^b
1	sealed tube, N₂	83
2	sealed tube, air	92
3	sealed tube, air	44^c
4	sealed tube, air	92^d
5	sealed tube, 60 °C, air	87
6	sealed tube, 2/3 equiv. of PCl₃, air	78

Conditions: (1) 1a (0.3 mmol), PCl₃ (0.3 mmol), and CH₃CN (0.6 mL) were stirred at 80 °C for 3 h under air and (2) MeOH (5.0 equiv.) was added and the mixture was stirred at 80 °C for 2 h.

GC yield based on 1a using dodecane as an internal standard.

MeOH (3.0 equiv.) was used.

MeOH (6.0 equiv.) was used.The bold in Table 1 means the optimal reaction condition.

Next, the generality of this transesterification was explored. We were pleased to find that the reaction of various tert-butyl esters with MeOH proceeded efficiently in one-pot to give the corresponding products in good to excellent yields. As shown in Table 2, both electron-rich and electron-deficient substrates provided the corresponding aryl esters (2a–h) under the optimized reaction conditions in good to excellent yields. A vinyl group at the para position was tolerated well (2i) and tert-butyl 2-naphthoate underwent this reaction smoothly to give 2j in 90% yield. Moreover, benzyl esters such as tert-butyl 2-(naphthalen-2-yl)acetate, tert-butyl 2-(p-tolyl)acetate, and tert-butyl 2-phenylpropanoate were also found to be suitable substrates (2k–m). The alkenyl ester tert-butyl cinnamate reacted readily to afford methyl cinnamate (2n) in 95% yield. It should be noted that alkyl esters, such as tert-butyl 3-phenylpropanoate and tert-butyl hexanoate, exhibited good reactivity, furnishing the expected products 2o and 2p in 96% and 94% yield, respectively.

Table 2.

Substrate scope with various tert-butyl esters.^a

Conditions: (1) 1 (1.3 mmol), PCl₃ (1.3 mmol), and CH₃CN (2.0 mL) were stirred in a sealed 25-mL Schlenk tube at 80 °C for 3 h under air and (2) MeOH (5.0 equiv.) was added and the mixture was stirred at 80 °C for 2 h. Yield of isolated products are given.

Step (1) was performed at 60 °C for 6 h and step (2) was performed at 60 °C for 2 h.

Steps (1) and (2) were performed at 100 °C for 3 and 2 h, respectively.

Steps (1) and (2) were performed at 60 °C for 3 and 2 h, respectively.

We next explored the reaction of tert-butyl benzoate with different alcohols under similar conditions (Table 3). Gratifyingly, by prolonging the reaction time to 11 h, ethanol and isopropanol were amenable to this transesterification and the expected products 2q and 2r were obtained in good to excellent yields. Notably, when sterically hindered alcohols, such as cyclohexanol and phenol, were subjected to the reaction, 87% and 81% yields of the products 2s and 2t were achieved, respectively. Benzyl alcohol provided the corresponding product 2u in a modest yield.

Table 3.

Substrate scope with different alcohols.^a

Conditions: (1) 1a (1.3 mmol), PCl₃ (1.3 mmol), and CH₃CN (2.0 mL) were stirred in a sealed tube at 80 °C for 3 h under air and (2) R¹OH (6.0 equiv.) was added and the mixture was stirred at 80 °C for 11 h. Yield of isolated products are given.

We subsequently investigated if this PCl₃-mediated system could be applicable for the aminolysis of tert-butyl esters (Table 4). For primary amines, such as aniline, 4-fluoroaniline, and 4-methoxyaniline, moderate-to-good yields of the amidated products 3a–c were obtained. Moreover, secondary amines, such as N-methylaniline and diphenylamine, were also successfully employed to give the amide products 3d and 3e in 83% and 82% yields, respectively. To our delight, this aminolysis reaction could also be extended to aliphatic amines and aliphatic tert-butyl esters giving products 3f–j.

Table 4.

PCl₃-mediated aminolysis of tert-butyl esters.^a

Conditions: (1) 1a (1.3 mmol), PCl₃ (1.3 mmol), and CH₃CN (2.0 mL) were stirred in a sealed tube at 80 °C for 3 h under air and (2) R²R³NH (1.0 equiv.) was added and the mixture stirred at 80 °C for 2 h. Isolated yields.

Step (2) was performed at 100 °C for 2 h.

Amine (3.0 equiv.) was used.

Steps (1) and (2) were performed at 60 °C for 6 and 2 h, respectively.

Step (2) was performed at 80 °C for 0.5 h.

Reactions to synthesize valuable skeletons of bioactive molecules were conducted to demonstrate the potential synthetic utility of this aminolysis reaction (Scheme 2). Thus, dimethylamine and morpholine were subjected to this reaction to afford the corresponding skeletons of bioactive molecules^30–32 in 77% and 75% yields, respectively (equations (1) and (2)). Interestingly, benzenesulfonamide could also be converted into the product 3m, which is the scaffold of the biologically active compound cyprosulfamide (equation (3)).³³

Scheme 2.

The synthesis of skeletons of bioactive molecules.

The value of this PCl₃-mediated system lies further on the scalability of the reaction. As depicted in Scheme 3, gram-scale reactions were conducted on 10-mmol scale with a reduced quantity of PCl₃ usage (2/3 equiv.) and the desired products, such as methyl benzoate and N,N-dibutylbenzamide, were obtained in 81% and 90% yields, respectively. As one molecule of PCl₃ has three chlorine atoms which can be utilized in the reaction, this may account for the lower PCl₃ loading.³⁴

Scheme 3.

Scale-up reactions.

A series of control experiments have been carried out to probe the mechanism (Scheme 4). A 93% yield of benzoyl chloride was generated when 1a and PCl₃ were stirred in CH₃CN at 80 °C for 3 h under air (equation (4)). This result indicated that acid chlorides are the key intermediates which react with alcohols and amines to afford the products. To study the formation of acid chlorides from esters, 1.5 equiv. of HCl instead of PCl₃ were subjected to the reaction and a 90% yield of benzoic acid and 8% of 2a were obtained, respectively (equations (5) and (6)). The reaction was suppressed in the presence of 2.0 equiv. of pyridine (equation (7)). We attribute the trace yield of 2a to the neutralization of HCl which was easily formed by the reaction of PCl₃ with water in air or in the solvent. These results indicate that HCl generated in situ plays an important role in the reaction. As we reported previously, benzoic acids can react with PCl₃ or the P-Cl reagent to afford acid chlorides.³⁴ Thus, there are two roles played by PCl₃ in this reaction: formation of HCl in situ and the chloride reagent.

Scheme 4.

Control experiments.

Based on the above results and our previous reports,^29,34 a possible mechanism has been proposed. As shown in Scheme 5, we considered two processes for this reaction. The first involves hydrolysis of ester 1 to give the corresponding acid 5 with the aid of HCl. Subsequent reaction of acid 5 with (OH)_nPCl_3-n (n = 0, 1, 2), then forms the corresponding acyl chlorides 4. The second is the complexation of 1 with 6 followed by the elimination of a tert-butyl cation to afford chlorides 7. The resulting intermediate 7 then reacts with HCl to afford 4. The reaction of 4 with the alcohol or amine provides the product 2 or 3, respectively.

Scheme 5.

Possible mechanisms.

Conclusion

In summary, using cheap and readily available PCl₃, an efficient transesterification and aminolysis of tert-butyl esters has successfully been demonstrated. Mechanistic studies revealed that the reaction proceeds via an acid chloride. This new method provides an efficient and simple protocol to synthesize a wide range of esters and amides from tert-butyl esters. Furthermore, this approach has been applied to the synthesis of the frameworks of bioactive molecules and is easily scaled up even when 2/3 equiv. of PCl₃ are used.

Experimental

Unless otherwise noted, all reactions were carried out in sealed oven-dried Schlenk tubes under air. Reagents and solvents were obtained from commercial suppliers and used without purification. Flash column chromatography was performed using 200–300 mesh silica gel. Visualization on thin-layer chromatography (TLC) was achieved by the use of UV light (254 nm). A FULI GC-9790II equipped with a flame ionization detector (FID) detector was used to analysis the reaction mixture. ¹H nuclear magnetic resonance (NMR) and ¹³C NMR spectra were recorded on a Bruker AV-II 500-MHz NMR spectrometer (¹H: 500 MHz, ¹³C: 125.76 MHz) in CDCl₃ or DMSO-d₆. The coupling constants J are given in Hz. Chemical shifts for ¹H NMR are referred to internal Me₄Si (0 ppm). GC-MS was recorded on a Shimadzu GCMS-QP2010 plus equipped with an electron ionization (EI) ion source. Substrates 1c,³⁵ 1d,³⁶ 1f,³⁷ 1g,³⁸ 1h–m,³⁹ 1n,³⁷ 1o,³⁹ and 1p³⁶ were synthesized according to the known methods.

Typical procedure for the preparation of the target molecules: Under air, tert-butyl ester 1 (1.3 or 0.3 mmol), PCl₃ (1.0 equiv.), and CH₃CN (0.6 mL) were added to a 25-mL sealed Schlenk tube equipped with a magnetic stir bar. The mixture was stirred at 80 °C for 3 h. Next, the corresponding alcohol (5.0 equiv.) or amine (1.0 or 3.0 equiv.) was added to the reaction and the mixture was stirred at the indicated temperature for the indicated amount of time. The mixture was then quenched with aqueous NaHCO₃ solution and extracted with EtOAc (×3). The combined organic layer was dried over MgSO₄ and filtered. After evaporation of the solvent under reduced pressure, the residue was purified by column chromatography on silica gel to give the analytically pure product 2 or 3.

Methyl benzoate (2a):⁴⁰ Colorless oil; yield: 86% (152.1 mg). Petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz, CDCl₃): δ 8.07–8.05 (m, 2H), 7.59–7.56 (m, 1H), 7.47–7.44 (m, 2H), 3.93 (s, 3H). ¹³C NMR (125.76 MHz CDCl₃): δ 167.2, 133.0, 130.1, 129.6, 128.4, 52.2. GC-MS (EI, 70 eV): m/z = 136 (M⁺).

Methyl 4-methylbenzoate (2b):⁴⁰ Colorless oil; yield: 72% (140.5 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.84 (d, J = 8.0 Hz, 2H), 7.14 (d, J = 8.0 Hz, 2H), 3.80 (s, 3H), 2.31 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 167.2, 143.6, 129.6, 129.1, 127.4, 51.9, 21.6. GC-MS (EI, 70 eV): m/z = 150 (M⁺).

Methyl 2,4,6-trimethylbenzoate (2c):⁴¹ Colorless oil; yield: 83% (192.1 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 6.66 (s, 2H), 3.70 (s, 3H), 2.11 (s, 6H), 2.09 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 170.6, 139.3, 135.2, 130.9, 128.4, 51.7, 21.1, 19.8. GC-MS (EI, 70 eV): m/z = 178 (M⁺).

Methyl 4-methoxybenzoate (2d):⁴⁰ White solid; yield: 81% (174.8 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.93–7.90 (m, 2H), 6.86–6.83 (m, 2H), 3.81 (s, 3H), 3.78 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 166.9, 163.3, 131.6, 122.6, 113.6, 55.4, 51.9. GC-MS (EI, 70 eV): m/z = 166 (M⁺).

Methyl 4-fluorobenzoate (2e):⁴² Colorless oil; yield: 85% (170.2 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 8.02–8.00 (m, 2H), 7.08–7.04 (m, 2H), 3.87 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 165.5, 165.2 (d, J_C-F = 252.2 Hz), 131.6 (d, J_C-F = 9.3 Hz), 125.9 (d, J_C-F = 2.6 Hz), 114.9 (d, J_C-F = 21.9 Hz), 51.6. GC-MS (EI, 70 eV): m/z = 154 (M⁺).

Methyl 4-chlorobenzoate (2f):⁴⁰ White solid; yield: 94% (207.7 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.90 (d, J = 8.5 Hz, 2H), 7.34 (d, J = 8.5 Hz, 2H), 3.84 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 165.8, 138.9, 130.5, 128.2, 128.1, 51.8. GC-MS (EI, 70 eV): m/z = 170 (M⁺).

Methyl 4-(trifluoromethyl)benzoate (2g):⁴⁰ Light yellow oil; yield: 93% (246.6 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 8.07 (d, J = 8.0 Hz, 2H), 7.63 (d, J = 8.5 Hz, 2H), 3.88 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 165.4, 133.9 (q, J_C-F = 32.7 Hz), 132.9, 129.5, 124.9 (q, J_C-F = 3.1 Hz), 123.1 (q, J_C-F = 272.8 Hz), 52.0. GC-MS (EI, 70 eV): m/z = 204 (M⁺).

Methyl 4-acetylbenzoate (2h):⁴³ White solid; yield: 64% (148.1 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 8.06 (d, J = 8.5 Hz, 2H), 7.94 (d, J = 8.5 Hz, 2H), 3.88 (s, 3H), 2.58 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 197.1, 165.8, 139.7, 133.4, 129.4, 127.7, 52.0, 26.4. GC-MS (EI, 70 eV): m/z = 178 (M⁺).

Methyl 4-vinylbenzoate (2i):⁴⁴ White solid; yield: 63% (132.7 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.92 (d, J = 8.5 Hz, 2H), 7.38 (d, J = 8.5 Hz, 2H), 6.70–6.64 (m, 1H), 5.79 (d, J = 17.5 Hz, 1H), 5.30 (d, J = 11.0 Hz, 1H), 3.83 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 166.4, 141.4, 135.5, 129.4, 128.8, 125.6, 116.0, 51.6. GC-MS (EI, 70 eV): m/z = 162 (M⁺).

Methyl 2-naphthoate (2j):⁴⁰ Light yellow solid; yield: 90% (217.6 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 8.54 (s, 1H), 7.89 (dd, J = 1.5 Hz, 8.5 Hz, 1H), 7.89 (d, J = 8.0 Hz, 1H), 7.81 (d, J = 8.5 Hz, 2H), 7.54–7.46 (m, 2H), 3.91 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 167.3, 135.5, 132.5, 131.1, 129.4, 128.3, 128.2, 127.8, 127.4, 126.7, 125.2, 52.3. GC-MS (EI, 70 eV): m/z = 186 (M⁺).

Methyl 2-(naphthalen-2-yl)acetate (2k):⁴⁵ White solid; yield: 70% (182.0 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.74–7.01 (m, 3H), 7.65 (s, 1H), 7.41–7.32 (m, 3H), 3.71 (s, 2H), 3.62 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 172.1, 133.5, 132.5, 131.5, 128.3, 128.0, 127.7, 127.7, 127.4, 126.2, 125.9, 52.2, 41.4. GC-MS (EI, 70 eV): m/z = 200 (M⁺).

Methyl 2-(p-tolyl)acetate (2l):⁴⁶ Colorless oil; yield: 96% (204.7 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.07–7.02 (m, 4H), 3.57 (s, 3H), 3.48 (s, 2H), 2.22 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 171.8, 136.3, 130.5, 128.9, 128.7, 51.6, 40.3, 20.6. GC-MS (EI, 70 eV): m/z = 164 (M⁺).

Methyl 2-phenylpropanoate (2m):⁴⁷ Light yellow oil; yield: 95% (202.5 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.39–7.34 (m, 4H), 7.31–7.28 (m, 1H), 3.78 (q, J = 7.0 Hz, 1H), 3.69 (s, 3H), 1.55 (d, J = 7.0 Hz, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 174.5, 140.1, 128.2, 127.0, 126.7, 51.6, 45.0, 18.2. GC-MS (EI, 70 eV): m/z = 164 (M⁺).

Methyl cinnamate (2n):⁴² Light yellow solid; yield: 95% (200.1 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.63 (d, J = 16.0 Hz, 1H), 7.47–7.45 (m, 2H), 7.33–7.30 (m, 3H), 6.38 (d, J = 16.0 Hz, 1H), 3.74 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 167.5, 144.9, 134.4, 130.3, 128.9, 128.1, 117.8, 51.7. GC-MS (EI, 70 eV): m/z = 162 (M⁺).

Methyl 3-phenylpropanoate (2o):⁴⁸ Light yellow oil; yield: 96% (204.7 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.19–7.16 (m, 2H), 7.11–7.08 (m, 3H), 3.55 (s, 3H), 2.85 (t, J = 7.5 Hz, 2H), 2.52 (t, J = 8.0 Hz, 2H). ¹³C NMR (125.76 MHz, CDCl₃): δ 172.9, 140.2, 128.1, 127.8, 125.8, 51.2, 35.3, 30.5. GC-MS (EI, 70 eV): m/z = 164 (M⁺).

Methyl hexanoate (2p):⁴⁰ Colorless oil; yield: 94% (158.9 mg). Eluent: petroleum ether. ¹H NMR (500 MHz CDCl₃): δ 3.60 (s, 3H), 2.23 (t, J = 7.5 Hz, 2H), 1.59–1.53 (m, 2H), 1.27–1.22 (m, 4H), 0.83 (t, J = 7.0 Hz, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 174.3, 51.4, 34.1, 31.3, 24.6, 22.3, 13.9. GC-MS (EI, 70 eV): m/z = 130 (M⁺).

Ethyl benzoate (2q):⁴⁷ Light yellow oil, yield 96% (187.2 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.99–7.97 (m, 2H), 7.50–7.46 (m, 1H), 7.38–7.35 (m, 2H), 4.31 (q, J = 7.5 Hz, 2H), 1.33 (t, J = 7.0 Hz, 3H); ¹³C NMR (125.76 MHz, CDCl₃): δ 166.7, 132.8, 130.5, 129.5, 128.3, 61.0, 14.4. GC-MS (EI, 70 eV): m/z = 150 (M⁺).

Isopropyl benzoate (2r):⁴⁷ Light yellow oil; yield: 84% (179.1 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.94–7.95 (m, 2H), 7.47–7.44 (m, 1H), 7.36–7.33 (m, 2H), 5.21–5.14 (m, 1H), 1.29 (d, J = 6.5 Hz, 6H). ¹³C NMR (125.76 MHz, CDCl₃): δ 166.1, 132.7, 130.9, 129.5, 128.3, 68.4, 22.0. GC-MS (EI, 70 eV): m/z = 164 (M⁺).

Cyclohexyl benzoate (2s):⁴⁹ Light yellow oil; yield: 87% (230.7 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 7.98–7.96 (m, 2H), 7.46–7.43 (m, 1H), 7.35–7.32 (m, 2H), 4.97–4.92 (m, 1H), 1.87–1.84 (m, 2H), 1.71–1.69 (m, 2H), 1.52–1.47 (m, 3H), 1.40–1.24 (m, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 166.0, 132.7, 131.0, 126.5, 128.3, 73.0, 31.7, 25.5, 23.7. GC-MS (EI, 70 eV): m/z = 204 (M⁺).

Phenyl benzoate (2t):⁴⁷ White solid; yield: 81% (208.5 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 8.15–8.13 (m, 2H), 7.58–7.55 (m, 1H), 7.46–7.42 (m, 2H), 7.38–7.34 (m, 2H), 7.22–7.17 (m, 1H), 7.15–7.13 (m, 2H). ¹³C NMR (125.76 MHz, CDCl₃): δ 165.2, 151.0, 133.6, 130.2, 129.6, 129.5, 128.6, 125.9, 121.8. GC-MS (EI, 70 eV): m/z = 198 (M⁺).

Benzyl benzoate (2u):⁴⁰ Colorless oil; yield: 52% (143.3 mg). Eluent: petroleum ether/EtOAc = 10/1. ¹H NMR (500 MHz CDCl₃): δ 8.17–8.15 (m, 2H), 7.62–7.59 (m, 1H), 7.53–7.44 (m, 6H), 7.42–7.39 (m, 1H), 5.44 (s, 2H). ¹³C NMR (125.76 MHz, CDCl₃): δ 166.5, 136.1, 133.1, 130.2, 129.8, 128.7, 128.5, 128.3, 128.3, 66.8. GC-MS (EI, 70 eV): m/z = 212 (M⁺).

N-phenylbenzamide (3a):⁵⁰ White solid; yield: 76% (194.6 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.81–7.78 (m, 3H), 7.58–7.57 (m, 2H), 7.50–7.47 (m, 1H), 7.44–7.41 (m, 2H), 7.31 (t, J = 8.0 Hz, 2H), 7.09 (t, J = 7.5 Hz, 1H). ¹³C NMR (125.76 MHz, CDCl₃): δ 165.8, 137.9, 135.0, 131.9, 129.1, 128.8, 127.0, 124.6, 120.2. GC-MS (EI, 70 eV): m/z = 197 (M⁺).

N-(4-Fluorophenyl)benzamide (3b):⁵¹ White solid; yield: 85% (237.6 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz DMSO-d₆) δ 10.30 (s, 1H), 7.97–7.94 (m, 2H), 7.82–7.78 (m, 2H), 7.61–7.57 (m, 1H), 7.55–7.51 (m, 2H), 7.22–7.17 (m, 2H). ¹³C NMR (125.76 MHz, DMSO-d₆) δ 165.9, 158.8 (d, J_C-F = 240.2 Hz) 136.0 (d, J_C-F = 2.5 Hz), 135.3, 132.1, 128.9, 128.1, 122.7, 115.6 (d, J_C-F = 22.6 Hz). GC-MS (EI, 70 eV): m/z = 215 (M⁺).

(4-Methoxyphenyl)benzamide (3c):⁵⁰ Light yellow solid; yield: 71% (209.5 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.79 (d, J = 7.5 Hz, 2H), 7.73 (brs, 1H), 7.48–7.45 (m, 3H), 7.42–7.39 (m, 2H), 6.85–6.82 (m, 2H), 3.74 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 165.7, 156.7, 135.0, 131.7, 131.0, 128.8, 127.0, 122.1, 114.3, 55.5. GC-MS (EI, 70 eV): m/z = 227 (M⁺).

N-Methyl-N-phenylbenzamide (3d):⁵⁰ Light yellow oil; yield: 83% (227.7 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.22–7.21 (m, 2H), 7.17–7.13 (m, 3H), 7.09–7.04 (m, 3H), 6.95 (d, J = 7.5 Hz, 2H), 3.42 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 170.7, 144.9, 135.9, 129.6, 129.2, 128.7, 127.7, 126.9, 126.5, 38.4. GC-MS (EI, 70 eV): m/z = 211 (M⁺).

N,N-Diphenylbenzamide (3e):⁵⁰ White solid; yield: 82% (291.1 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.39–7.38 (m, 2H), 7.23–7.20 (m, 5H), 7.16–7.08 (m, 8H). ¹³C NMR (125.76 MHz, CDCl₃): δ 170.8, 143.9, 136.1, 130.2, 129.2, 129.1, 127.9, 127.5, 126.4. GC-MS (EI, 70 eV): m/z = 273 (M⁺).

Benzylbenzamide (3f):⁵⁰ White solid, yield 70% (192.0 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.73–7.71 (m, 2H), 7.45–7.42 (m, 1H), 7.38–7.34 (m, 2H), 7.29–7.21 (m, 5H), 6.36 (brs, 1H), 4.58 (d, J = 5.5 Hz, 2H). ¹³C NMR (125.76 MHz, CDCl₃): δ 167.4, 138.2, 134.4, 131.6, 128.8, 128.6, 128.0, 127.7, 127.0, 44.2. GC-MS (EI, 70 eV): m/z = 211 (M⁺).

N,N-Dibutylbenzamide (3g):⁵² Light yellow oil; yield: 90% (272.6 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.30–7.25 (m, 5H), 3.41–3.10 (m, 4H), 1.57–1.32 (m, 6H), 1.04–0.70 (m, 8H). ¹³C NMR (125.76 MHz, CDCl₃): δ 171.6, 137.4, 129.0, 128.3, 126.4, 48.7, 44.4, 30.8, 29.6, 20.3, 19.7, 13.9, 13.6. GC-MS (EI, 70 eV): m/z = 233 (M⁺).

N-Phenyl-2-(p-tolyl)acetamide (3h):⁵³ White solid; yield: 90% (263.3 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.34–7.33 (m, 2H), 7.20–7.17 (m, 3H), 7.14–7.10 (m, 4H), 7.01–6.98 (m, 1H), 3.61 (s, 2H), 2.29 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 169.51, 137.68, 137.43, 131.33, 129.95, 129.46, 128.93, 124.44, 119.87, 44.41, 21.15. GC-MS (EI, 70 eV): m/z = 225 (M⁺).

N,3-Diphenylpropanamide (3i):⁵³ White solid; yield: 89% (260.3 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.75–7.70 (m, 1H), 7.35–7.33 (m, 2H), 7.17–7.06 (m, 7H), 6.98–6.95 (m, 1H), 2.90 (t, J = 8.0 Hz, 2H), 2.52 (t, J = 8.0 Hz, 2H). ¹³C NMR (125.76 MHz, CDCl₃): δ 171.02, 140.66, 137.89, 128.96, 128.65, 128.41, 126.38, 124.39, 120.30, 39.25, 31.64. GC-MS (EI, 70 eV): m/z = 225 (M⁺).

N-Phenylhexanamide (3j):⁵⁴ White solid; yield: 48% (119.2 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.53–7.51 (m, 2H), 7.38 (brs, 1H), 7.30 (t, J = 8.0 Hz, 2H), 7.11–7.08 (m, 1H), 2.35 (t, J = 7.5 Hz, 2H), 1.75–1.69 (m, 2H), 1.38–1.33 (m, 4H), 0.90 (t, J = 7.0 Hz, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 171.61, 138.00, 128.98, 124.18, 119.84, 37.80, 31.44, 25.37, 22.45, 13.96. GC-MS (EI, 70 eV): m/z = 191 (M⁺).

N,N-Dimethylcinnamamide (3k):⁵⁵ White solid; yield: 77% (134.8 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.69 (d, J = 15.5 Hz, 1H), 7.56–7.54 (m, 2H), 7.41–7.34 (m, 3H), 6.91 (d, J = 15.5 Hz, 1H), 3.18–3.09 (m, 6H). ¹³C NMR (125.76 MHz, CDCl₃): δ 166.7, 142.4, 135.3, 129.6, 128.8, 127.8, 117.4, 37.5, 36.0. GC-MS (EI, 70 eV): m/z = 175 (M⁺).

(E)-1-Morpholino-3-phenylprop-2-en-1-one (3l):⁵⁶ White solid; yield: 75% (162.8 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 7.63 (d, J = 15.5 Hz, 1H), 7.47–7.45 (m, 2H), 7.33–7.28 (m, 3H), 6.78 (d, J = 15.5 Hz, 1H), 3.66–3.62 (m, 8H). ¹³C NMR (125.76 MHz, CDCl₃): δ 165.6, 143.3, 135.1, 129.8, 128.9, 127.8, 116.5, 66.9, 46.2, 42.5. GC-MS (EI, 70 eV): m/z = 217 (M⁺).

4-Methoxy-N-(phenylsulfonyl)benzamide (3m):⁵⁷ White solid; yield: 81% (235.7 mg). Eluent: petroleum ether/EtOAc = 5/1. ¹H NMR (500 MHz CDCl₃): δ 9.47 (brs, 1H), 8.10–8.08 (m, 2H), 7.75–7.32 (m, 2H), 7.59–7.56 (m, 1H), 7.50–7.46 (m, 2H), 6.81–6.80 (m, 2H), 3.74 (s, 3H). ¹³C NMR (125.76 MHz, CDCl₃): δ 164.0, 163.8, 138.6, 134.0, 130.2, 129.0, 128.6, 123.1, 114.2, 55.6. GC-MS (EI, 70 eV): m/z = 291 (M⁺).

Supplemental Material

sj-pdf-1-chl-10.1177_1747519820987530 – Supplemental material for PCl3-mediated transesterification and aminolysis of tert-butyl esters via acid chloride formation

Supplemental material, sj-pdf-1-chl-10.1177_1747519820987530 for PCl3-mediated transesterification and aminolysis of tert-butyl esters via acid chloride formation by Xiaofang Wu, Lei Zhou, Fangshao Li and Jing Xiao in Journal of Chemical Research

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: J.X. was financially supported by the National Natural Science Foundation of China (No. 21703061) and the Natural Science Foundation of Hunan Province (No. 2017JJ3081).

ORCID iD

Jing Xiao

Supplemental material

Supplemental material for this article is available online.

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