ASYMMETRIC CYCLOPROPANATION BY REACTION OF A GAMMA-CHLOROMETHYLATED CHIRAL VINYLIC SULFOXIDE WITH ALLYLMAGNESIUM BROMIDE

An optically active vinylic sulfoxide bearing a leaving group at the g amma-position was stereoselectively transformed into a chiral cyclopro pane by means of a Michael addition with an allylmagnesium bromide. Th e Michael induced ring-closure reaction requires both allylmagnesium b romide as a nucleophile and chloride as a leaving group for high diast ereoselectivity. The absolute stereochemistry of the cycloadduct was c onfirmed by X-ray analysis.