Are Glycosyl Triflates Intermediates in the Sulfoxide Glycosylation Method? A Chemical and 1H, 13C, and 19F NMR Spectroscopic Investigation
摘要:
The title question is addressed by low-temperature H-1, C-13, and F-19 NMR spectroscopies in CD2Cl2 as well as by the preparation of authentic samples from glycopyranosyl bromides and AgOTf. At -78 degrees 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 degrees C in CD2Cl2 and allowed to warm gradually until decomposition was detected by H-1 and F-19 NMR spectroscopy. The decomposition temperature and products are functions of the protecting groups employed.