Stereospecific synthesis of α-C-glycosyl derivatives ('α-C-glycosides') of N-acetylneuraminic acid by samarium-mediated reductive desulfonylation of a glycosyl phenylsulfone

A samarium-mediated Barbier reaction was performed to afford N-acetylneuraminic acid α-C-glycosyl compounds ('α-C-glycosides') in excellent yield. The neuraminic acid phenyl sulfone or 2-pyridyl sulfone derivatives reacted with ketones or aldehydes resulting in the instantaneous and stereospecific formation of Neu5Ac α-C-glycosides. The phenyl and the 2-pyridyl sulfone derivatives were equally effective in this reaction. Finally, this procedure was successfully applied to the preparation of C-disaccharide, α-Neu5Ac-(2-&gt6) Gal.