Synlett 2006(12): 1962-1964  
DOI: 10.1055/s-2006-947363
LETTER
© Georg Thieme Verlag Stuttgart · New York

Bu4N[AuCl4]-Catalyzed Synthesis of Highly Substituted Furans from 2-(1-Alkynyl)-2-alken-1-ones in Ionic Liquids: An Air-Stable and Recyclable Catalytic System

Xueyuan Liua, Zhenliang Pana, Xingzhong Shua, Xinhua Duana, Yongmin Liang*a,b
a State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. of China
Fax: +86(931)8912582; e-Mail: liangym@lzu.edu.cn;
b State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. of China
Further Information

Publication History

Received 6 April 2006
Publication Date:
24 July 2006 (online)

Abstract

The cyclization of 2-(1-alkynyl)-2-alken-1-ones proceeded smoothly in the presence of various nucleophiles with a ­catalytic amount of Bu4N[AuCl4] in [bmim]BF4, leading to the formation of highly substituted furans. This system is air-stable and ­recyclable. The catalyst is inexpensive and readily available.

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Representative Procedure.
To the appropriate 2-(1-alkynyl)-2-alken-1-one (0.2 mmol) and nucleophile (1.5 equiv) in [bmim]BF4 (1 mL) was added Bu4N[AuCl4] (1 mol%). The mixture was stirred at r.t. for 3 h unless otherwise specified. The mixture was extracted with Et2O (2 ¥ 5 mL). The isolated ether layer was concentrated in vacuo and the residue was purified by flash chromatography on silica gel.

12

Recycling Procedure.
To the 2-phenylethynyl-2-cyclohexen-1-one (1.0 mmol) and MeOH (1.5 equiv) in [bmim]BF4 (3 mL) was added Bu4N[AuCl4] (1 mol%). The mixture was stirred at r.t. for 3 h. The product was extracted from the reaction mixture by addition of Et2O (2 ¥ 20 mL). The ether layer was separated. The ionic liquid layer containing Au catalyst was pumped for several minutes and reused for the next reaction.

13

Spectral Data of the Representative Product 2a.
1H NMR (300 MHz, CDCl3): δ = 1.79-1.93 (m, 2 H), 1.94-2.05 (m, 2 H), 2.59-2.75 (m, 2 H), 3.43 (s, 3 H), 4.28 (t, J = 3.9 Hz, 1 H), 6.64 (s, 1 H), 7.18-7.23 (m, 1 H), 7.31-7.36 (m, 2 H), 7.60-7.63 (m, 2 H). 13C NMR (75 MHz, CDCl3): δ = 18.8, 23.2, 28.3, 56.1, 72.3, 105.3, 119.9, 123.3, 126.8, 128.5, 131.1, 152.2, 152.8.