Synthesis of 2-(trimethylsilyl)ethyl α-D-mannopyranosides revisited

Glycosylation of 2-(trimethylsilyl)ethanol with various ethyl 1-thioglycosides, which were activated with N-iodosuccinimide and silver triflate, was studied. The starting thioglycosides, some prepared for the first time, were obtained conventionally from the corresponding alpha-1-acetates. When beta-1-acetates were more readily available, these were converted to the alpha-anomers by anomerization, prior to the glycosylation. Using ethyl 1-thioglycosides as glycosyl donors, especially those bearing a pivaloyl or a nonparticipating group at O-2, the corresponding 2-(trimethylsilyl)ethyl alpha-D-mannopyranosides were obtained in excellent yields.