INTRODUCTION

2-Substituted benzoxazoles are important building blocks that are extensively used in many areas [1–3] requiring new synthetic strategies to be developed by organic chemists. Several methods have been employed using 2-aminophenol as substrate under sulfur-medi­ated transition metal-free conditions (Scheme 1) [4–8]. Benzoxazole has also been reported as a substrate in these reactions [9–14]. However, literature reports on the use of styrene as a substrate are still rare [15].

Styrene has been applied widely in organic synthe­sis for the construction of C–C and C–X bonds in recent years [16–22], and great advances have been made recently in the construction of heterocycles [23–28]. For example, Deng et al. [26] reported ortho-C–H sulfuration/cyclization of aniline with elemental sulfur for efficient synthesis of 2-substituted benzo­thiazoles (Scheme 1). Han et al. [15] recently reported elemental sulfur-promoted formation of benzoxazole/benzothiazole with carbon atoms of a C=C double bond as a one-carbon donator, but the substrate scope was not broad. However, the development of metal-free protocols for the synthesis of 2-(arylmethyl)­benzoxazoles is still pressing [4–8, 18, 19]. In view of this need and continuing with our sulfur-related research [29–34], we report here metal-free cyclization of 2-aminophenols with styrenes to give 2-(aryl­methyl)­benzoxazoles (Scheme 1).

Scheme
scheme 1

1.

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RESULTS AND DISCUSSION

Initially, we used unsubstituted styrene (1a), 2-amino­phenol (2a, 2.0 equiv), elemental sulfur (2.0 equiv), and NaHCO3 (1.5 equiv) in N-methylpyr­rolidone (NMP) at 110°C under an air atmosphere to explore the reaction, and the target product, 2-benzyl-1,3-benzoxazole (3aa) was isolated in 57% yield (Scheme 2; Table 1, entry no. 1). We then tried other bases such as KHCO3, K3PO4, N-methylpiperidine (NMPP) or pyridine (Table 1, entry nos. 2–5). To our delight, 3aa could be obtained in 68% yield in NMP with K2HPO4 as a base (Table 1, entry no. 6), although lower yields were obtained when other organic solvents were used (Table 1, entry nos. 7–13). The yield was not improved by conducting the reaction at a higher (120°C) or lower temperature (100°C) (Table 1, entry nos. 14, 15). Altering the amounts of elemental sulfur, 2a, or K2HPO4 did not improve the yield (Table 1, entry nos. 16–20). The yield of 3aa was 61% when 1a was replaced with β-bromostyrene as substrate (Table 1, entry no. 21). However, no desired product was obtained when allylbenzene was employed as substrate (Table 1, entry no. 22).

Scheme
scheme 2

2.

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Table 1. Optimization of the reaction conditionsa
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We studied the scope of the proposed protocol for the synthesis of 2-(arylmethyl)benzoxazoles 3 using a series of substituted styrenes (Scheme 3). Many substituents on the aromatic rings of the styrenes were tolerated in the reaction, and the corresponding products 3ab–3ar were isolated in moderate to good yields (47–78%). In general, meta-substituted styrenes gave lower yields than their para-substituted analogs (3ab, 3af–3ai, 3am–3ap, 3ar). Furthermore, 1- and 2-vinylnaphthalenes smoothly reacted under the op­timal conditions to give the desired products 3as and 3at in 49 and 62% yields, respectively. We also performed the reaction of 2-aminophenol (2a) and 4-methyl­styrene (1b) on a gram-scale, and compound 3ab was isolated in 65% yield (1.16 g) from 8 mmol of 1b. Differently substituted 2-aminophenols were also reacted with styrene (1a) under the optimal conditions to afford the required products 3ba–3ia in moderate to good yields (45–74%); the highest yield (3ga, 74%) was obtained from 2-amino-5-fluorophenol (1g).

Scheme
scheme 3

3.

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Special experiment was carried out to provide an insight into the reaction mechanism (Scheme 4). 2-Aminophenol (2a) was acylated with phenylacetyl chloride (1.0 equiv) in the presence of pyridine (1.1 equiv) in methylene chloride to give amide 4 in 82% yield [35]. Amide 4 was treated with Lawesson’s reagent (1.0 equiv) in anhydrous methylene chloride to afford thioamide 4′ which was detected by mass spectrometry (see Supplementary Materials), and the latter underwent cyclization to furnish the target product 3aa.

Scheme
scheme 4

4.

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Based on known reports [25, 26, 36, 37] and our experimental results, a possible mechanism is proposed in Scheme 5. The reaction of 2a with elemental sulfur produces intermediate A [38, 39], and the addition of A to styrene 1a gives intermediate B which undergoes oxidation and reacts with another equivalent of 2a to give C. N-(2-Hydroxyphenyl)-2-phenylethanethio­amide D is produced from C via S–S bond cleavage, and the subsequent cyclization generates interme­diate E. Loss of hydrogen sulfide from the latter yields the final product 3aa [40]. Alternatively, S–S bond cleavage in C, followed by cyclization, gives oxazoline intermediate F which is oxidized to 3aa.

Scheme
scheme 5

5.

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Some chemical transformations of benzoxazole 3aa were also studied (Scheme 6). The oxidation of 3aa (0.5 mmol) with CuI (20 mol %) and AcOH (1.0 equiv) in DMSO for 24 h (1 atm O2) afforded 2-benzoyl­benzoxazole 5 in 89% yield. Benzoxazole 3aa was smoothly alkylated with n-hexyl bromide (1.2 equiv) in the presence of K3PO4 (0.78 equiv) in NMP under nitrogen to give 82% of 6. Likewise, the alkylation of 3aa with benzyl chloride (1.2 equiv) in the presence of Cs2CO3 (1.2 equiv) in DMA under a nitrogen atmo­sphere afforded 2-(1,2-diphenylethyl)benzoxazole 7 in 60% (isolated) yield.

Scheme
scheme 6

6.

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EXPERIMENTAL

Under otherwise noted, materials were obtained from commercial suppliers and used without further purification. All experiments were conducted in a sealed pressure vessel. The 1H NMR spectra were recorded at 300, 400, or 500 MHz in CDCl3 (δ 7.26 ppm). The 13C NMR spectra were recorded at 75, 100, or 125 MHz in CDCl3 (δC 77.0 ppm). The 19F NMR spectra were recorded at 282 MHz in CDCl3. The 1H and 13C chemical shifts were measured relative to tetramethylsilane (TMS) as internal standard. The high-resolution mass spectra were recorded using a Q-TOF mass spectrometer. Elemental analyses were carried out with a Vario MICRO cube analyzer (Germany). Flash column chromatography was per­formed over silica gel (200–300 mesh).

2-Benzyl-1,3-benzoxazole (3aa) [5]. A mixture of styrene (2a, 24 μL, 0.2 mmol), 2-aminophenol (1a, 43.6 mg, 0.4 mmol), elemental sulfur (12.8 mg, 0.4 mmol), K2HPO4 (52.3 mg, 0.3 mmol), and NMP (0.6 mL) was placed in a sealed pressure vessel (10 mL) containing a magnetic stirring bar. The vessel was capped, and the mixture was stirred at 110°C for 18 h under air atmosphere. After the reaction was complete (TLC), the mixture was cooled to room temperature, and treated with ethyl acetate (15 mL) and water (10 mL). The organic phase was separated, washed with brine, dried, filtered, and evaporated under reduced pressure, and the residue was purified by silica gel column chromatography using petroleum ether–ethyl acetate as eluent (20:1). Yield 28 mg (68%), light yellow solid, mp 107–109°C; published data [41]: 108–110°C; Rf 0.3 (petroleum ether–ethyl acetate, 20:1). 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.67–7.71 m (1H), 7.44–7.49 m (1H), 7.27–7.40 m (7H), 4.28 s (2H).

Compounds 3ab–3ia were synthesized in a similar way.

2-(4-Methylbenzyl)-1,3-benzoxazole (3ab) [5]. Yield 35 mg (78%), light yellow solid, mp 47–49°C, Rf 0.3 (petroleum ether–ethyl acetate, 20:1). 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.67–7.70 m (1H), 7.44–7.48 m (1H), 7.26–7.31 m (4H), 7.16 d (J = 8.0 Hz, 2H), 4.24 s (2H), 2.33 s (3H).

2-(4-Ethylbenzyl)-1,3-benzoxazole (3ac). Yield 36 mg (75%), light yellow oil, Rf 0.3 (petroleum ether–ethyl acetate, 30:1). 1H NMR spectrum (500 MHz, CDCl3), δ, ppm: 7.69–7.70 m (1H), 7.45–7.47 m (1H), 7.26–7.32 m (4H), 7.19 d (2H, J = 7.9 Hz), 4.25 s (2H), 2.64 q (2H, J = 7.6 Hz), 1.23 t (3H, J = 7.6 Hz). 13C NMR spectrum (125 MHz, CDCl3), δC, ppm: 165.4, 151.1, 143.3, 141.4, 132.0, 128.9, 128.3, 124.6, 124.1, 119.8, 110.4, 34.9, 28.4, 15.4. Mass spectrum: m/z 238.12230 [M + H]+. Found, %: C 80.66; H 6.46; N 5.99. C16H15NO. Calculated, %: C 80.98; H 6.37; N 5.90. M + H 238.12264.

2-(4-Propylbenzyl)-1,3-benzoxazole (3ad). Yield 36 mg (72%), light yellow oil, Rf 0.3 (petroleum ether–ethyl acetate, 30:1). 1H NMR spectrum (500 MHz, CDCl3), δ, ppm: 7.69–7.70 m (1H), 7.45–7.47 m (1H), 7.26–7.31 m (4H), 7.16 d (2H, J = 7.9 Hz), 4.25 s (2H), 2.57 t (2H, J = 7.6 Hz), 1.60–1.67 m (2H), 0.94 t (3H, J = 7.3 Hz). 13C NMR spectrum (125 MHz, CDCl3), δC, ppm: 165.4, 151.1, 141.7, 141.4, 132.0, 128.9, 128.8, 124.6, 124.1, 119.8, 110.4, 37.6, 34.9, 24.4, 13.8. Mass spectrum: m/z 252.13788 [M + H]+. Found, %: C 81.06; H 6.86; N 5.63. C17H17NO. Calcu­lat­ed, %: C 81.24; H 6.82; N 5.57. M + H 252.13829.

2-(4-Butylbenzyl)-1,3-benzoxazole (3ae) [30]. Yield 35 mg (66%), light yellow oil, Rf 0.4 (petroleum ether–ethyl acetate, 20:1). 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.65–7.70 m (1H), 7.42–7.46 m (1H), 7.24–7.29 m (4H), 7.15 d (2H, J = 8.0 Hz), 4.23 s (2H), 2.58 t (2H, J = 7.7 Hz), 1.53–1.61 m (2H), 1.29–1.38 m (2H), 0.91 t (3H, J = 7.3 Hz).

2-(4-Methoxybenzyl)-1,3-benzoxazole (3af) [5]. Yield 28 mg (58%), light yellow solid, Rf 0.2 (petro­leum ether–ethyl acetate, 10:1), mp 45–47°C; published data [42]: mp 43–45°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.67–7.69 m (1H), 7.45–7.49 m (1H), 7.25–7.33 m (4H), 6.87–7.91 m (1H), 4.21 s (3H), 3.79 s (3H).

2-(4-Fluorobenzyl)-1,3-benzoxazole (3ag) [5]. Yield 25 mg (56%), light yellow solid, Rf (petroleum ether–ethyl acetate, 20:1), mp 35–37°C. 1H NMR spec­trum (400 MHz, CDCl3), δ, ppm: 7.69–7.76 m (1H), 7.31–7.48 m (5H), 7.05 d (2H, J = 7.7 Hz), 4.25 s (2H).

2-(4-Chlorobenzyl)-1,3-benzoxazole (3ah) [5]. Yield 32 mg (65%), light yellow solid, Rf 0.3 (petro­leum ether–ethyl acetate, 20:1), mp 79–81°C; published data [43]: mp 78–80°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.68–7.69 m (1H), 7.46–7.47 m (1H), 7.26–7.32 m (6H), 4.24 s (2H).

2-(4-Bromobenzyl)-1,3-benzoxazole (3ai) [44]. Yield 30 mg (52%), light yellow solid, Rf 0.4 (petro­leum ether–ethyl acetate, 20:1), mp 93–95°C; published data [44]: mp 92–95°C. 1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.67–7.72 m (1H), 7.46–7.48 m (3H), 7.26–7.32 m (4H), 4.22 s (2H).

2-(4-tert-Butylbenzyl)-1,3-benzoxazole (3aj) [13]. Yield 31 mg (59%), light yellow solid, Rf 0.3 (petro­leum ether–ethyl acetate, 25:1), mp 71–73°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.68–7.70 m (1H), 7.45–7.48 m (1H), 7.38 d (2H, J = 8.4 Hz), 7.32 d (2H, J = 8.4 Hz), 7.28–7.30 m (2H), 4.25 s (2H), 1.31 s (9H).

2-([1,1′-Biphenyl]-4-ylmethyl)-1,3-benzoxazole (3ak) [10]. Yield 39 mg (69%), light yellow solid, Rf 0.2 (petroleum ether–ethyl acetate, 20:1), mp 96–98°C; published data [45]: mp 91°C. 1H NMR spec­trum (400 MHz, CDCl3), δ, ppm: 7.70–7.73 m (1H), 7.57–7.59 m (4H), 7.42–7.50 m (5H), 7.36 d (1H, J = 7.0 Hz), 7.30–7.32 m (2H), 4.33 s (2H).

2-[4-(Trifluoromethyl)benzyl]-1,3-benzoxazole (3al) [10]. Yield 31 mg (56%), light yellow solid, Rf 0.3 (petroleum ether–ethyl acetate, 30:1), mp 51–53°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.69–7.71 m (1H), 7.61 d (2H, J = 8.1 Hz), 7.45– 7.51 m (3H), 7.25–7.32 m (2H), 4.32 s (2H).

2-(3-Methylbenzyl)-1,3-benzoxazole (3am) [13]. Yield 26 mg (59%), light yellow oil, Rf 0.3 (petroleum ether–ethyl acetate, 20:1). 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.73–7.75 m (1H), 7.49–7.51 m (1H), 7.28–7.36 m (3H), 7.22 d (2H, J = 7.4 Hz), 7.13 d (2H, J = 7.3 Hz), 4.27 s (2H), 2.38 s (3H).

2-(3-Methoxybenzyl)-1,3-benzoxazole (3an) [5]. Yield 26 mg (54%), light yellow solid, Rf 0.2 (petro­leum ether–ethyl acetate, 10:1), mp 71–73°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.68–7.72 m (1H), 7.46–7.48 m (1H), 7.25–7.32 m (3H), 6.82– 6.98 m (3H), 4.25 s (2H), 3.80 s (3H).

2-(3-Fluorobenzyl)-1,3-benzoxazole (3ao) [10]. Yield 23 mg (50%), light yellow oil, Rf 0.3 (petroleum ether–ethyl acetate, 20:1). 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.69–7.72 m (1H), 7.46–7.49 m (1H), 7.25–7.34 m (3H), 7.09–7.17 m (2H), 6.96–7.00 m (1H), 4.27 s (2H).

2-(3-Chlorobenzyl)-1,3-benzoxazole (3ap) [30]. Yield 27 mg (56%), light yellow oil, Rf 0.3 (petroleum ether–ethyl acetate, 20:1). 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.68–7.71 m (1H), 7.45–7.48 m (1H), 7.38 s (1H), 7H), 7.10 s (1H), 4.26 s (2H), 2.45 s (3H).

2-(2-Chlorobenzyl)-1,3-benzoxazole (3aq) [5]. Yield 29 mg (60%), yellow oil, Rf 0.3 (petroleum ether–ethyl acetate, 30:1). 1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.71–7.73 m (1H), 7.39–7.50 m (3H), 7.26–7.33 m (4H), 4.45 s (2H).

2-(3-Bromobenzyl)-1,3-benzoxazole (3ar) [46]. Yield 27 mg (47%), yellow oil, Rf 0.3 (petroleum ether–ethyl acetate, 20:1). 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.69–7.71 m (1H), 7.41–7.55 m (3H), 7.55–7.58 m (1H), 7.20–7.31 m (4H), 4.24 s (2H).

2-(Naphthalen-1-ylmethyl)-1,3-benzoxazole (3as) [47]. Yield 25 mg (49%), light yellow solid, Rf 0.2 (petroleum ether–ethyl acetate, 20:1), mp 67–69°C; published data [47]: mp 68°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 8.16 d (1H, J = 3.6 Hz), 7.80–7.85 m (2H), 7.67 d (1H, J = 3.3 Hz), 7.39– 7.52 m (5H), 7.23–7.29 m (2H), 4.70 s (2H).

2-(Naphthalen-2-ylmethyl)-1,3-benzoxazole (3at) [5]. Yield 32 mg (62%), light yellow solid, Rf 0.2 (petroleum ether–ethyl acetate, 20:1), mp 60–62°C. 1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.82–7.86 m (4H), 7.69–7.72 m (1H), 7.43–7.52 m (4H), 7.28–7.34 m (2H), 4.44 s (2H).

2-Benzyl-5-methyl-1,3-benzoxazole (3ba) [48]. Yield 27 mg (61%), light yellow solid, Rf 0.3 (petro­leum ether–ethyl acetate, 20:1). mp 48–50°C; published data [48]: mp 49.5–51°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.26–7.47 m (7H), 7.10 s (1H), 4.26 s (2H), 2.45 s (3H).

2-Benzyl-6-methyl-1,3-benzoxazole (3ca) [5]. Yield 29 mg (66%), light yellow solid, Rf 0.3 (petro­leum ether–ethyl acetate, 20:1), mp 49–51°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.53–7.55 m (1H), 7.26–7.44 m (6H), 7.10 d (1H, J = 7.3 Hz), 4.24 s (2H), 2.45 s (3H).

2-Benzyl-5-methoxy-1,3-benzoxazole (3da) [30]. Yield 27 mg (56%), light yellow solid, Rf 0.2 (petro­leum ether–ethyl acetate, 10:1), mp 147–149°C. 1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.26–7.39 m (6H), 7.18 s (1H), 6.89 d (1H, J = 8.9 Hz), 4.25 s (2H), 3.83 s (3H).

2-Benzyl-5-fluoro-1,3-benzoxazole (3ea) [13]. Yield 22 mg (48%), light yellow solid, Rf 0.3 (petro­leum ether–ethyl acetate, 30:1), mp 46–48°C; published data [13]: mp 48–49°C. 1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.26–7.37 m (7H), 6.99–7.05 m (1H), 4.26 s (2H).

2-Benzyl-5-chloro-1,3-benzoxazole (3fa) [5]. Yield 22 mg (45%), light yellow solid, Rf 0.3 (petro­leum ether–ethyl acetate, 20:1), mp 45–47°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.67 d (1H, J = 1.9 Hz), 7.26–7.44 m (7H), 4.27 s (2H).

2-Benzyl-6-fluoro-1,3-benzoxazole (3ga). Yield 34 mg (74%), light yellow solid, Rf 0.3 (petroleum ether–ethyl acetate, 25:1), mp 124–126°C. 1H NMR spectrum (500 MHz, CDCl3), δ, ppm: 7.61 d.d (1H, J = 8.7, 4.9 Hz), 7.34–7.38 m (1H), 7.28–7.31 m (1H), 7.19 d.d (1H, J = 8.0, 3.3 Hz), 7.03–7.07 m (1H), 4.26 s (2H). 13C NMR spectrum (125 MHz, CDCl3), δC, ppm: 166.0, 151.1, 139.7, 134.3 d (J = 8.1 Hz), 130.5, 128.9 d (J = 12.6 Hz), 127.4, 125.0, 120.2, 119.9 d (J = 16.6 Hz), 112.2 d (J = 40.9 Hz), 111.1, 35.1. Mass spectrum: m/z 228.10199 [M + H]+. Found, %: C 73.86; H 4.41; N 6.14. C14H10NOF. Cal­cu­lated, %: C 74.00; H 4.44; N 6.16. M + H 228.08192.

2-Benzyl-6-chloro-1,3-benzoxazole (3ha) [5]. Yield 27 mg (56%), light yellow solid, Rf 0.3 (petro­leum ether–ethyl acetate, 20:1), mp 50–52°C. 1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.59 d (1H, J = 8.6 Hz), 7.47 s (1H), 7.29–7.38 m (6H), 4.26 s (2H).

2-Benzylnaphtho[2,3-d][1,3]oxazole (3ia) [49]. Yield 35 mg (67%), light yellow solid, Rf 0.3 (petro­leum ether–ethyl acetate, 20:1), mp 140–143°C; pub­lished data [49]: mp 140–142°C. 1H NMR spectrum (400 MHz, CDCl3), δ, ppm: 7.77–7.82 m (2H), 7.55 s (1H), 7.44–7.46 m (1H), 7.26–7.36 m (7H), 4.50 s (2H).

N-(2-Hydroxyphenyl)-2-phenylacetamide (4) [35]. Yield 1.862 g (82%), light yellow solid, mp 148–150°C; published data [46]: 149–150°C. 1H NMR spec­trum (400 MHz, DMSO-d6), δ, ppm: 9.75 br.s (1H), 9.31 br.s (1H), 7.76 d (1H, J = 7.9 Hz), 7.22– 7.37 m (5H), 6.83–6.95 m (2H), 6.72–6.77 m (1H), 3.74 s (2H).

1-(1,3-Benzoxazol-2-yl)-1-phenylmethanone (5) [50]. Yield 99 mg (89%), light yellow solid, Rf 0.4 (petroleum ether–ethyl acetate, 30:1), mp 73–75°C; published data [51]: mp 74°C. 1H NMR spectrum (500 MHz, CDCl3), δ, ppm: 8.54 d (2H, J = 7.6 Hz), 7.92 d (1H, J = 8.0 Hz), 7.64–7.69 m (2H), 7.51– 7.56 m (3H), 7.43–7.46 m (1H).

2-(1-Phenylheptyl)-1,3-benzoxazole (6) [11]. Yield 120 mg (82%), colorless liquid, Rf 0.3 (petroleum ether–ethyl acetate, 60:1). 1H NMR spectrum (500 MHz, CDCl3), δ, ppm: 7.74–7.76 m (1H), 7.43–7.48 m (3H), 7.27–7.37 m (5H), 4.26 t (1H, J = 7.8 Hz), 2.39–2.46 m (1H), 2.12–2.20 m (1H), 1.29–1.39 m (8H), 0.89 t (3H, J = 6.9 Hz).

2-(1,2-Diphenylethyl)-1,3-benzoxazole (7) [52]. Yield 90 mg (60%), colorless oil, Rf 0.3 (petroleum ether–ethyl acetate, 50:1). 1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.74–7.77 m (1H), 7.45–7.48 m (1H), 7.14–7.40 m (12H), 4.49 t (1H, J = 7.8 Hz), 3.81 d.d (1H, J = 7.8, 5.9 Hz), 3.43 d.d (1H, J = 7.8, 5.9 Hz).

CONCLUSIONS

A sulfur-mediated metal-free protocol has been developed to prepare 2-(arylmethyl)benzoxazoles. Dipotassium hydrogen phosphate was found to be an effective base for this transformation with broad functional group tolerance. The reactions proceeded in moderate to good yields, and a gram-scale reaction was carried out. Preliminary mechanistic investigations suggested participation of thioamide intermediate, namely N-(2-hydroxyphenyl)-2-phenylethanethio­amide. Further application of this methodology is ongoing in our laboratory.