Ferric Chloride: A Mild and Versatile Reagent for the Formation of 1,6-Anhydro Glucopyranoses.

A novel method for the preparation of 1,6-anhydro glucopyranoses (mono- and disaccharides) utilizing anhydrous FeCl3 as Lewis acid is described. Treatment of methyl 6-O-benzyl and 6-O-p-methoxybenzyl-α/β d-glucopyranosides derivatives with FeCl3 in CH2Cl2 at room temperature and 40°C afforded 1,6-anhydro glucopyranosides in moderate to good yields, through a debenzylation and intramolecular glycosidation in one step. A plausible reaction pathway is proposed.