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Synlett 2011(20): 3026-3030  
DOI: 10.1055/s-0031-1289908
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© Georg Thieme Verlag Stuttgart ˙ New York

Regiospecific Synthesis of 3,4-Dihydrocoumarins via Substrate-Controlled [1,3]- or [3,3]-Sigmatropic Rearrangement

Xiangsheng Xu*, Xiaoqing Li, Xinhuan Yan, Hanshen Wang, Yun Deng, Jiangbin Shao
College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
Fax: +86(571)88320799; e-Mail: future@zjut.edu.cn;
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Publication History

Received 21 October 2011
Publication Date:
28 November 2011 (online)

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Abstract

A regiospecific synthesis of 3,4-dihydrocoumarin derivatives has been achieved involving tandem rearrangement-cyclization of (E)-2-(aryloxymethyl)alk-2-enoates catalyzed by a Pd/Cu bimetallic system. Unexpected substrate-controlled [1,3]- or [3,3]-sigmatropic rearrangement was observed in the transformations.

Key words

[1,3]-sigmatropic rearrangement - [3,3]-sigmatropic ­rearrangement - palladium/copper bimetallic catalyst - substrate-­controlled selectivity - 3,4-dihydrocoumarin

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General Experimental Procedure and Spectroscopic Data
Compound 1a (268.3 mg, 1.0 mmol), Pd(OAc)2 (11.2 mg, 0.05 mmol), Cu(OTf)2 (18.1 mg, 0.05 mmol), and DCE (2 mL) were added to a 10 mL sealed vessel protected under Ar. Then the reaction mixture was stirred under reflux conditions for 15 h. Upon completion of the reaction, the resulting mixture was diluted with CH2Cl2 (10 mL) and filtered through Celite. After evaporation of the solvent under vacuum, the residue was purified by column chromatography on silica gel (200-300 mesh) using cyclohexane-EtOAc (12:1) as eluent to give pure 2a (153.7 mg, 65%) as a white solid. ¹H NMR (CDCl3, 500 MHz): δ = 4.09 (d, J = 2.0 Hz, 2 H), 7.01-7.18 (m, 3 H), 7.35-7.57 (m, 6 H), 7.99 (t, J = 2.0 Hz, 1 H).