Asymmetric cyclopropanation of (5S,S-S)-3-p-tolylsulfinyl-5-ethoxyfuran-2(5H)-one with sulfonium ylides: influence of the sulfur ylide substituents on stereoselectivity

摘要

The cyclopropanation of title compound 1 with various sulfur ylides has been examined. A very high pi-facial selectivity was observed in the reaction with diphenylsulfonium ylides, Ph2S=CRR' (anti attack with respect to the alkoxy group in 1 is clearly preferred) whereas the endo-selectivity was found when Rnot equalR' is dependent on their relative size. Reactions with dimethylsulfonium ylides Me2S=CRR' occurred with a moderate pi-facial selectivity and exo-selectivity, the former being dependent on the solvent polarity. The stereochemical course of the cyclopropanation reactions is rationalized in terms of steric and electrostatic interactions. (C) 2004 Elsevier Ltd. All rights reserved.