Reinvestigation of SnCl catalyzed efficient synthesis of 2,3-unsaturated glycopyranosides.

The Ferrier rearrangement is a powerful tool to prepare 2,3-unsaturated glycopyranosides. We have reinvestigated SnCl catalyzed Ferrier rearrangements through direct allylic substitution of the hydroxyl group at the C-3 position of glycals, resulting in the formation of stereoselective 2,3-unsaturated glycosides at 0 °C. The catalytic amount of SnCl (0.1 equiv.) was successfully used to promote this transformation on 3,4,6-tri-O-acetyl-D-glucal, 3,4,6-tri-O-acetyl-D-galactal and 3,4-di-O-acetyl-D-arabinal using various nucleophiles viz alcohols, azide and thiols to form a variety of 2,3-unsaturated glycopyranosides (pseudoglycals). This straightforward process is notable for its strong anomeric selectivity, excellent yields and shorter reaction time.