2‐Deoxyglycosyl fluorides in oligosaccharide synthesis

Abstract

Abstract 3,4‐Di‐ O ‐acetyl‐2,6‐dibromo‐2,6‐dideoxy‐α‐ D ‐mannopyranosyl fluoride ( 1 ) was treated with Lewis acid catalysts to give α‐glycosides exclusively. Reactions with α‐ and β‐glucosyl analogs yield α/β mixtures under the same conditions. With no assistance of anchimeric substituents at C‐2 the stereoselectivity is directed by a glycosyl fluoride/catalyst/solvent complex. As shown in the 2‐deoxy‐ arabino ‐hexopyranosyl series this leads to improved α/β ratios and yields.