Nucleophilic addition of potassium alkynyltrifluoroborates to D-glucal mediated by BF3 x OEt2: highly stereoselective synthesis of alpha-C-glycosides.

A convenient, mild and highly stereoselective method for C-glycosidation (alkynylation) of D-glucal with various potassium alkynyltrifluoroborates, mediated by BF3x OEt2 and involving oxonium intermediates, preferentially provides the alpha-acetylene glycoside products with good yields.