Glycosyl triflates, which serve as important intermediates in glycosylation reactions, were generated and accumulated by the low-temperature electrochemical oxidation of thioglycosides such as thioglucosides, thiogalactosides, and thiomannosides in the presence of tetrabutylammonium triflate (Bu(4)NOTf) as a supporting electrolyte. Thus-obtained solutions of glycosyl triflates (glycosyl triflate pools) were characterized by low-temperature NMR measurements. The thermal stability of glycosyl triflates and their reactions with glycosyl acceptors were also examined.

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).

Glycosyl sulfonium ions, which serve as persistent glycosyl cation equivalents, were prepared by the addition of diorganosulfides to an electrochemically generated glycosyl triflate. Low-temperature and variable-temperature NMR studies were performed to reveal the structure, stability, and reactivity of glycosyl sulfonium ions. The glycosyl sulfonium ions could be used as storable intermediates for reactions with various glycosyl acceptors including thioglycosides to give the corresponding disaccharides.