The Lewis acid catalyzed addition reactions of allylic sulfides to methyl propiolate (MP) and dimethyl acetylenedicarboxylate (DMAD) have been investigated. The stereochemical outcome is considerably influenced by the Lewis acid. While the AlCl,-catalyzed reactions of MP afforded E adducts 2 as the major products, the use of ZnC12 resulted in the inversion of stereoselectivity to give Z adducts 3 mainly. The reactions of DMAD showed the similar ...