Direct Ferrier rearrangement on unactivated glycals catalyzed by indium(III) chloride

Anhydrous InCl3 has been shown to efficiently catalyze the Ferrier rearrangement by a direct allylic substitution of the hydroxyl group at C-3 position of glycals to afford the corresponding 2,3-unsaturated glycosides in high yields at ambient temperature. This methodology obviates the need for protecting and/or activating the C-3 hydroxyl group of glycals. The reaction works in equal ease with both 4,6-di-O-benzyl-d-glucal and 4,6-di-O-benzyl-d-galactal. The mildness of InCl3 makes this approach compatible for glycosyl acceptors with acid labile groups. The generality of the reaction has been demonstrated with a diversity of alcohols, phenols, and sugar nucleophiles.