Copper-Catalyzed (4+1) Cascade Annulation of Terminal Alkynes with 2-(Tosylmethyl)anilines: Synthesis of 2,3-Disubstituted Indoles

Xu Yan, Chun-Fang Liu, Xian-Tao An, Xiao-Min Ge, Qing Zhang, Lin-Han Pang, Xu Bao* and Chun-An Fan*

*College of Chemistry and Chemical Engineering, Lanzhou University, 222 Tianshui Nanlu, Lanzhou 730000, China, Email: baoxulzu.edu.cn, fanchunanlzu.edu.cn

X. Yan, C.-F. Liu, X.-T. An, X.-M. Ge, Q. Zhang, L.-H. Pang, X. Bao, C.-A. Fan, Org. Lett., 2021, 23, 8905-8909.

DOI: 10.1021/acs.orglett.1c03402

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Abstract

A Cu-catalyzed (4+1) cascade annulation of terminal alkynes as one-carbon synthons with 2-(tosylmethyl)anilines provides synthetically and structurally interesting 2,3-disubstituted indoles.

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General Procedure

To an oven dried 10 mL Schlenck flask equipped with a stirring bar was added 2-(tosylmethyl)aniline (0.2 mmol), CuI (0.02 mmol), and Cs₂CO₃ (0.2 mmol). The resultant mixture was degassed three times by argon, and then terminal alkyne (0.4 mmol), DBU (0.04 mmol), and PhCl (2 mL) were added under argon atmosphere. The reaction mixture was stirred in an oil bath at 120°C for the indicated time until 2-(tosylmethyl)aniline was consumed (monitored by TLC). Then the reaction mixture was purified by flash column chromatography on silica gel eluting with petroleum ether/ethyl acetate (V_{Petroleum ether}/V_EtOAc = 60:1 to V_{Petroleum ether}/V_EtOAc = 20:1), giving the corresponding product 2,3-disubstituted indole.

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Key Words

indoles

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ID: J54-Y2021