Stereo- and regio-selectivity of diethylaminosulfur trifluoride as a fluorinating reagent for methyl glycosides.

Methyl glycopyranosides reacted with diethylaminosulfur trifluoride (DAST) in the absence of solvent to yield methyl dideoxy-difluoro and deoxy-fluoro glycopyranosides. Methyl alpha-D-glycopyranosides produced 6-deoxy-6-fluoro- and 4,6-dideoxy-4,6-difluoro derivatives with Walden inversion at C-4. Methyl beta-D-glucopyranoside also produced a 3,6-dideoxy-3,6-difluoro derivative, with Walden inversion at C-3. Methyl 6-O-trityl-alpha-D-glucopyranoside, reacted with DAST to yield the corresponding 4-deoxy-4-fluorogalactopyranoside derivative.