Anomerization and transglycosylation reactions of permethylated methyl d-glycopyranosides

초록

The anomerization reactions of permethylated methyl d-glycopyranosides in the presence of various Lewis acid catalysts, such as Me<inf>3</inf>SiOTf, Me<inf>3</inf>SiOMs, BF<inf>3</inf>·OEt<inf>2</inf>, or TiCl<inf>4</inf> were examined in dichloromethane solution. β Anomers of the glycosides anomerized to the α anomer very rapidly, but the anomerizations in the opposite direction were slower. Transglycosylation reactions of the glycosides in the presence of similar catalysts and ethanol gave preferably the α anomers with most substrates employed. No anomerization was observed in the case of the α-mannoside, probably because the α anomer is strongly favored at equilibrium. Nevertheless, transglycosylation took place. © 1993.