[1,2]- vs [2,3]-Wittig Rearrangement in Carbohydrate Derived Alkenyl Systems.

A simple and efficient strategy for the regio- and stereoselective synthesis of carbon-branched sugar derivatives is described. The successful implementation of Wittig rearrangement on substrates derived by Ferrier rearrangement of various glycals and 3-O-alkenyl glycals is studied extensively. A highly selective [1,2]- or [2,3]-Wittig rearrangement is revealed that provides a novel class of stereodefined 3-C-branched glycals and C-glycosides, which are otherwise difficult to obtain.