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Synlett 2005(18): 2739-2742  
DOI: 10.1055/s-2005-918928
LETTER
© Georg Thieme Verlag Stuttgart · New York

One-Pot Synthesis of Benzo[b]thiophenes and Naphtho[2,1-b]thiophenes in the Presence of Acidic and Basic Supported Reagents

Tadashi Aoyama*a, Toshio Takidoa, Mitsuo Kodomarib
a Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University, Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan
Fax: +81(3)32590818; e-Mail: aoyama@chem.cst.nihon-u.ac.jp;
b Department of Applied Chemistry, Shibaura Institute of Technology, Shibaura, Minato-ku, Tokyo 108-8548, Japan
Further Information

Publication History

Received 28 July 2005
Publication Date:
10 October 2005 (online)

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Abstract

A simple and efficient method has been developed for the synthesis of benzo[b]thiophenes and naphtho[2,1-b]thiophenes from aryl thiols and α-halo ketones by using an acid- and a base-supported reagent system, Na2CO3/SiO2-PPA/SiO2. Reaction of α-halo ketones with aryl thiols is promoted by Na2CO3/SiO2 to afford α-phenylthio ketones, which cyclizes in the presence of PPA/SiO2 to give the corresponding arylthiophenes in one-pot.

Key words

one-pot synthesis - benzo[b]thiophenes - naphtho[2,1-b]thiophenes - supported reagents

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Typical Procedure. A mixture of α-haloketone (1 mmol), arylthiol (1 mmol), Na2CO3/SiO2 (1.0 g, 1.5 mmol) and PPA/SiO2 (3.5 g, 10 wt%) in chlorobenzene (15 mL) was stirred at 135 °C for 6 h, and then used supported reagents were removed by filtration. The filtrate was evaporated to leave crude product, which was purified by flash column chromatography to give the desired product.

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Preparation of Na 2 CO 3 /SiO 2 .
Silica gel [Wakogel C-200 (Wako Pure Chemical Ind. LTD.), 16.82 g] was added to a solution of sodium carbonate (30 mmol, 3.18 g) in distilled H2O, and the mixture was stirred at r.t. for 0.5 h. Then, H2O was removed by rotary evaporator under reduced pressure, and the resulting reagent was dried in vacuo (10 mmHg) at 160 °C for 5 h.

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Preparation of PPA/SiO 2 .
The PPA (2.0 g) and CHCl3 (100 mL) were placed in a round-bottom flask, and the mixture was stirred at 50 °C for 1 h. SiO2 [Wakogel C-200 (Wako Pure Chemical Ind. Ltd.), 18.0 g], which was dried in vacuo at 160 °C for 2 h, was added to the mixture, and the mixture was stirred for another 1 h. Then, CHCl3 was removed with rotary evaporator and the resulting solid was dried in vacuo at r.t. for 3 h.

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Compound 3b: mp 46-47 °C. 1H NMR (400 MHz, CDCl3): δ = 2.33 (3 H, s), 2.46 (3 H, s), 4.17 (2 H, s), 7.09 (1 H, d, J = 8.3 Hz), 7.18-7.29 (5 H, m), 7.42 (1 H, s), 7.59 (1 H, d, J = 8.3 Hz). 13C NMR (100 MHz, CDCl3): δ = 11.7, 21.5, 34.4, 121.5, 121.8, 125.4, 126.4, 127.3, 128.4, 128.5, 133.5, 135.7, 137.7, 139.8, 141.1. HRMS (TOF-CI): m/z calcd for C17H17S [MH+]: 253.1050; found: 253.1056.
Compound 3d: mp 60-61 °C. 1H NMR (400 MHz, CDCl3): δ = 2.36 (3 H, s), 2.47 (3 H, s), 4.20 (2 H, s), 7.07 (1 H, d, J = 7.3 Hz), 7.18-7.30 (6 H, m), 7.48 (1 H, d, J = 7.6 Hz). 13C NMR (100 MHz, CDCl3): δ = 11.9, 20.2, 34.4, 119.1, 124.1, 124.3, 126.4, 128.3, 128.5, 128.5, 131.6, 137.2, 138.7, 139.8, 140.7. HRMS (TOF-CI): m/z calcd for C17H17S [MH+]: 253.1050; found: 253.1044.
Compound 3e: 1H NMR (400 MHz, CDCl3): δ = 2.33 (3 H, s), 4.19 (2 H, s), 7.21-7.32 (5 H, m), 7.36 (1 H, dd, J = 8.5, 2.0 Hz), 7.56 (1 H, d, J = 8.5 Hz), 7.76 (1 H, d, J = 2.0 Hz). 13C NMR (100 MHz, CDCl3): δ = 11.7, 34.4, 118.0, 123.5, 124.3, 126.6, 126.6, 127.0, 128.5, 128.6, 137.2, 139.3, 139.9, 142.6. HRMS (EI): m/z calcd for C16H13BrS [M+]: 315.9921; found: 315.9922.
Compound 3f: 1H NMR (400 MHz, CDCl3): δ = 2.33 (3 H, s), 3.88 (3 H, s), 4.18 (2 H, s), 6.92 (1 H, dd, J = 8.8, 2.4 Hz), 7.08 (1 H, d, J = 2.4 Hz), 7.21-7.31 (5 H, m), 7.59 (1 H, d, J = 8.8 Hz). 13C NMR (100 MHz, CDCl3): δ = 11.8, 34.5, 55.6, 104.3, 113.4, 122.8, 126.5, 127.4, 128.4, 128.5, 130.9, 139.1, 139.7, 141.9, 157.4. HRMS (TOF-CI): m/z calcd for C17H17OS [MH+]: 269.1000; found: 269.1001.
Compound 3g: mp 98-100 °C. 1H NMR (400 MHz, CDCl3): δ = 2.80 (3 H, s), 4.30 (2 H, s), 7.20-7.32 (5 H, m), 7.48-7.59 (2 H, m), 7.65 (1 H, d, J = 8.8 Hz), 7.75 (1 H, d, J = 8.8 Hz), 7.93 (1 H, dd, J = 8.0, 1.2 Hz), 8.71 (1 H, d, J = 8.5 Hz). 13C NMR (100 MHz, CDCl3): δ = 16.9, 34.5, 120.7, 123.3, 124.5, 124.7, 125.8, 126.5, 128.4, 128.6, 129.0, 130.4, 130.5, 132.1, 134.7, 136.5, 137.5, 139.8. HRMS (TOF-CI): m/z calcd for C20H17S [MH+]: 289.1050; found: 289.1049.
Compound 3k: mp 103-104 °C. 1H NMR (400 MHz, CDCl3): δ = 1.24 (3 H, t, J = 7.1 Hz), 4.22 (2 H, q, J = 7.1 Hz), 4.29 (2 H, s), 7.41 (1 H, s), 7.50-7.62 (2 H, m), 7.72 (1 H, d, J = 8.7 Hz), 7.85 (1 H, d, J = 8.7 Hz), 7.95 (1 H, dd, J = 8.0, 1.2 Hz), 8.43 (1 H, d, J = 8.3 Hz). 13C NMR (100 MHz, CDCl3): δ = 14.1, 38.4, 61.1, 121.1, 122.9, 124.9, 125.3, 125.7, 126.2, 129.0, 129.9, 130.8, 131.9, 132.8, 139.4, 170.9. HRMS (TOF-CI): m/z calcd for C16H15O2S [MH+]: 271.0792; found: 271.0798.
Compound 3m: mp 166-168 °C. 1H NMR (400 MHz, CDCl3): δ = 7.15-7.29 (6 H, m), 7.36-7.45 (6 H, m), 7.51 (1 H, d, J = 8.5 Hz), 7.75 (1 H, d, J = 8.8 Hz), 7.89 (2 H, d, J = 8.5 Hz). 13C NMR (100 MHz, CDCl3): δ = 120.4, 123.7, 124.8, 125.6, 125.7, 127.4, 127.8, 128.2, 128.8, 128.9, 129.7, 130.1, 130.8, 132.2, 134.5, 134.5, 135.7, 137.1, 138.3, 139.9. HRMS (TOF-CI): m/z calcd for C24H17S [MH+]: 337.1050; found: 337.1045.