Thermodynamics versus kinetics in hetero-Michael cyclizations: a highly stereoselective approach to access both epimers of a C-d-mannopyranoside

A simple method for the stereocontrolled synthesis of both α and β pseudo-anomers of a thio-functionalized C-glycoside is described. A 2,3:4,6-di-O-isopropylidene manno scaffold is employed to allow a strict control of the diastereoselectivity of the base-catalyzed intramolecular hetero-Michael addition of an alcohol to a vinyl sulfone, by simply changing the temperature of the reaction.