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Synlett 2005(13): 2047-2051  
DOI: 10.1055/s-2005-872239
LETTER
© Georg Thieme Verlag Stuttgart · New York

Indium Trichloride Catalyzed Synthesis of 2-Aryl-3-aminobenzofuran ­Derivatives by a Three-Component Reaction of Phenols, Arylglyoxal ­Monohydrates and para-Toluenesulfonamide

Cong-Xi Chena,b, Li Liua, Dong-Peng Yanga, Dong Wang*a, Yong-Jun Chen*a
a Laboratory of Chemical Biology, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, P. R. China
Fax: +86(10)62554449; e-Mail: yjchen@iccas.ac.cn;
b Graduate School of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100080, P. R. China
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Publication History

Received 15 May 2005
Publication Date:
22 July 2005 (online)

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Abstract

A concise and efficient synthetic approach to 2-aryl-3-aminobenzofuran derivatives via an InCl3-catalyzed three-component reaction of arylglyoxal monohydrates, phenols and para-toluenesulfonamide has been developed. The benzofuran derivatives were obtained in good to excellent yields while the formation of α-diketones as by-products was effectively inhibited. The influences of reaction temperature, solvent and the order of the addition were also investigated.

Key words

benzofuran - phenol - indium trichloride - three-component reaction - arylglyoxal monohydrate

13

Unpublished results.

16

Typical Experimental Procedure.
Phenylglyoxal monohydrate (1a, 167 mg, 1.1 mmol), TsNH2 (171 mg, 1.0 mmol) and InCl3 (22 mg, 0.1 mmol) were mixed in 10 mL CH2Cl2 at r.t. and stirred for 30 min, then p-(t-Bu)PhOH (2a, 150 mg, 1.0 mmol) was added and the reaction system was warmed 40 °C. TLC showed that the starting materials were consumed completely about 6 h and cooled the reaction mixture to r.t. and 10 mL of H2O was added to quench the reaction. The aqueous layer was extracted with CH2Cl2 (3 × 20 mL) and organic solvent was combined and dried with anhyd Na2SO4. The solvent was evaporated and the residuum was purified by silica gel column chromatography (EtOAc-n-hexane, 1:6 in volume) to give benzofuran product 3aa in 82% yield and its analytic data are as follows: mp 163-164 °C. IR (neat): ν = 3291, 2961, 1597, 1478, 1446, 1397, 1362, 1331, 1167, 1092, 883, 816, 768, 709, 690, 666 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.15 (s, 9 H), 2.27 (s, 3 H), 6.20 (s, 1 H), 6.81 (s, 1 H), 7.05-7.08 (d, 2 H, J = 8.1 Hz), 7.19-7.34 (m, 5 H), 7.57-7.59 (d, 2 H, J = 8.1 Hz), 7.86-7.89 (t, 2 H, J = 8.0 Hz). 13C NMR (75 MHz, CDCl3): δ = 21.5, 31.5, 34.6, 110.7, 112.5, 115.1, 123.1, 126.5, 127.5, 128.4, 128.6, 129.0, 129.0, 129.7, 136.9, 144.0, 146.2, 151.0, 152.1. HRMS (FAB): m/z calcd for C25H25NO3S [M]+: 419.1550; found: 419.1552. Anal. Calcd for C25H25NO3S: C, 71.57; H, 6.01; N, 3.34. Found: C, 71.38; H, 6.09; N, 3.13.