Stereoselective 2-deoxy-β-O-glycoside synthesis based on remote activation of novel oxathiine donors

Stable glyco-fused 1,4-oxathiine derivatives, prepared by inverse electron-demand Diels-Alder reactions between suitable 1-glycals and 3-thioxopentane-2,4-dione, have been transformed into unusual glycosyl donors which, after "remote activation", react efficiently with glycosyl acceptors to afford 2-thio-beta -O-glycosides with total stereoselectivity. Several O-nucleophiles were successfully glycosylated. Reductive removal of sulfur transformed the 2-thio-beta -O-glycosides into the corresponding 2-deoxy-beta -O-glycosides without affecting the stereochemistry of the anomeric carbon atom.