Transglycosylation of Permethylated Methyl D-Glycopyranosides in the Presence of Trimethylsilyl Trifluoromethanesulfonate

초록

Transglycosylation reactions among methyl 2,3,4,6-tetra-O-methyl-D-glycopyranosides and isomeric butyl alcohols or cyclohexanol took place in the presence of trimethylsilyl triflouromethanesulfonate (TMSOTf) in dichloromethane. The extent of the reaction after 1 h and 24 from mixing was determined by gas chromatography (GC). Anomerization of the substrate took place during the course of transglycosylation, which favors α anomer regardless of the anomeric configurations of the starting glycosides. Transglycosylation also favors the α anomer regardless of the steric bulkiness of the alcohol. tert-Butyl alcohol did not give any transglycosylation, suggesting the steric hindrance of approaching the bulky alcohol to the oxonium intermediate. A mechanism for the transglycosylation have been proposed.