Highly 1,2-trans Stereoselective Allylations of 1,2-O-Isopropylidene-Protected Glycofuranosides

Abstract

A remarkable bicyclic acetal template effect is responsible for the complete 1,2-trans stereoselectivity achieved in Lewis acid promoted allylations of 1,2-O-isopropylidene-protected furanosides [Eq. (1)]. This stereoselectivity occurs regardless of the other substituents on the tetrahydrofuran ring. The bicyclic acetal acts as a basic, stable anomeric protecting group, and activates the carbohydrate anomeric position and directs the stereochemical outcome of the substitution reaction at this center.