On the Influence of the C2−O2 and C3−O3 Bonds in 4,6-O-Benzylidene-Directed β-Mannopyranosylation and α-Glucopyranosylation

Abstract

The synthesis of 4,6-O-benzylidene-protected 2-deoxyarabino-, 3-deoxyarabino-, and 3-deoxyribothioglycosides is described and their glycosylation reactions, with activation by either 1-benzenesulfinyl piperidine/trifluoromethansulfonic anhydride or diphenyl sulfoxide/trifluoromethanesulfonic anhydride, studied. In contrast to the corresponding 4,6-O-benzylidene-protected glucosyl and mannosyl donors, which are α- and β-selective, respectively, poor diastereoselectivity is observed in all cases. The reasons for this poor selectivity are discussed in terms of the interaction between the C2−O2 and C3−O3 bonds in the glucosyl and mannosyl donors and of the influence of this interaction on the ease of formation of the intermediate glycosyl oxacarbenium ions.