Alpha- and beta-glycosyl sulfonium ions: generation and reactivity.

Low-temperature electrochemical oxidation of thioglycosides gave glycosyl triflates from which glycosyl sulfonium ions were produced (see scheme). The latter were characterized by NMR spectroscopy and cold-spray mass spectrometry as a mixture of alpha- and beta-isomers (45:55). The alpha-glycosyl sulfonium ion exhibited higher reactivity than the beta-glycosyl sulfonium ion in the reaction with methanol, which gave a mixture of alpha- and beta-methyl glycosides (41:59).