Anomerization and transglycosylation reactions of permethylated methyl D-glycopyranosides

Article abstract of DOI:10.1016/0008-6215(93)84183-7

The anomerization reactions of permethylated methyl D-glycopyranosides in the presence of various Lewis acid catalysts, such as Me₃SiOTf, Me₃SiOMs, BF₃ · OEt₂, or TiCl₄ 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. The anomerization reactions of permethylated methyl D-glycopyranosides in the presence of various Lewis acid catalysts, such as Me₃SiOTf, Me₃SiOMs, BF₃·OEt₂, or TiCl₄ were examined in dichloromethane solution. β Anomers of the glycosides anomerized to the α anomer very rapidly, but the anomerization 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 amerization was observed in the case of the α-mannoside, probably because the α anomer is strongly favored at equilibrium. Nevertheless, transglycosylation took place.