Are Glycosyl Triflates Intermediates in the Sulfoxide Glycosylation Method? A Chemical and 1H, 13C, and 19F NMR Spectroscopic Investigation

The title question is addressed by low-temperature 1 H, 13 C, and 19 F NMR spectroscopies in CD 2 Cl 2 as well as by the preparation of authentic samples from glycopyranosyl bromides and AgOTf. At −78 °C glycosyl triflates are cleanly generated with either nonparticipating or particpating protecting groups at O-2. The glycosyl triflates identified in this manner were allowed to react with methanol, resulting in the formation of methyl glycosides. Glycosyl triflates were generated at −78 °C in CD 2 Cl 2 and allowed to warm gradually until decomposition was detected by 1 H and 19 F NMR spectroscopy. The decomposition temperature and products are functions of the protecting groups employed.