SYNTHESIS OF 2-(TRIMETHYLSILYL)ETHYL α-d-MANNOPYRANOSIDES REVISITED

Abstract

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 α-1-acetates. When β-1-acetates were more readily available, these were converted to the α-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 α-d-mannopyranosides were obtained in excellent yields.

Keywords:

• 2-(Trimethylsilyl)ethyl glycosides
• Glycosylation
• NIS/AgOTf
• Anomerization

Acknowledgments

Notes

^aNo physical constants or spectral data were reported for this substance, and the compound, as well as its HO-2-free precursor, are erroneously shown (Ref. [5]) as α-anomers.

^bThat ratio had not changed when, in a separate experiment, the reaction time was extended to 48 h, as showed by ¹H NMR spectroscopy. The two anomers show almost identical mobility on TLC.