New α-selective thermal glycosylation of acetyl-protected 2-acetamido-2-deoxy-β-d-glucopyranosyl diphenylphosphinate

This paper describes new α-selective thermal glycosylation using acetyl-protected 2-acetamido-2-deoxy-β-d-glucopyranosyl diphenylphosphinate (4) as a glycosyl donor. When the glycosylation of 4 with 1-hexanol was carried out under various conditions, the conditions using trimethylsilyl trifluoromethanesulfonate as a promoter in nitromethane at reflux temperature were most suitable for the formation of the α anomer. The glycosylation of 4 with the other common alcohols gave corresponding α-glycosides in relatively high yields under the conditions. When cholesterol, a very steric hindered alcohol, was used as a glycosyl acceptor, α-glycoside was also produced predominantly.