The intramolecular addition of incipient amine anions to chiral (E)- and (Z)-vinyl sulfoxides occurs in the same diastereofacial sense, giving chiral isoquinoline and piperidine derivatives that differ in relative stereochemistry at C-2. In contrast, the conjugate addition reactions of (E)- and (Z)-/?-styryl p-tolyl sulfoxide with benzylamine and LiCH(C02Et)2 are diastereoconvergent processes. The same major diastereomeric product is obtained in each case. We have attempted to rationalize the stereochemical outcome of the addition of nucleophiles to chiral vinyl sulfoxides according to the type of nucleophilic reagent employed (either chelating/hydrogen bonding or nonchelating) and from a consideration of possible transition states. © 1990, American Chemical Society. All rights reserved.