Highly diastereoselective formation of 1,2,3-trisubstituted cyclopropane derivatives

A highly diastereoselective formation of cyclopropane derivatives was reported. When the chiral phenylvinyl epoxide reacted with lithiated 2-alkyl-1,3-dithiane or lithiated alkyl carbonanion in the presence of HMPA, cyclopropanes bearing stereochemistry at all three positions on the ring were readily obtained in high yields of 80-97% and high dr values of 68:32-99:1. This reaction was supposed to be a tandem conjugation addition-epoxide opening sequence. [reaction: see text]