Resolution of secondary alcohols using 2-acyl-3-phenyl-l-menthopyrazoles as enantioselective acylating agents
作者:Choji Kashima、Saori Mizuhara、Yohei Miwa、Yukihiro Yokoyama
DOI:10.1016/s0957-4166(02)00472-x
日期:2002.8
The chelation of AlCl3 with N-acylpyrazoles leads to structural fixation of the acyl moiety and an acceleration in the rate of acylation of secondary alcohols. The chiral environment of the fixed acyl moiety of 2-acyl-3-phenyl-1-menthopyrazole 2 causes diastereofacial selectivity in the reaction with secondary alcohols, and thus 2 behaves as an enantioselective acylating agent. By the use of 2.4 molar equivalents of racemic 1-phenylethanol 3a, 2-acetyl-3-phenyl-1-menthopyrazole 2a afforded (S)-1-phenylethyl acetate (S)-4aa enantioselectively and unreacted 3a was recovered with (R)-configuration. Furthermore, the inverse configurational preferences were observed to give (R)-4aa and (S)-3a by the addition of strongly basic amines, which sometimes behaved as catalysts for enolate formation from 2 and AlCl3. These dramatic changes in stereoselective preference should be useful properties of 2-acyl-3-phenyl-1-menthopyrazole 2 as an enantioselective acylating agent. (C) 2002 Elsevier Science Ltd. All rights reserved.