A novel approach to the stereocontrolled synthesis of C-vinyl β-d-galactopyranosides

Reaction of a lithiated dithiinyl reagent with a O-perbenzylated d-glycono-δ-lactone readily generates the corresponding masked C-vinyl galactosides in high yields and full β-selectivity. Removal of the sulfur mask renders the free vinyl aglycone with the vinyl group in either the Z or E configuration, depending on the desulfurization conditions chosen.