To a solution of dry pyridine (0.456 mL) in methylene chloride (20 mL) cooled to -15° C. was added trifluoromethanesulfonic anhydride (0.864 mL). The mixture was stirred during 15 min at -10° C., then methyl 2,3,4-tri-O-benzyl-β-D-glucopyranoside (1.2 g, 2.58 mmol) in methylene chloride (30 mL) was added [P. Kovac, J. Alfoldi and M. Kosik, Chem. Zvesti 28, 820, (1974)]. The mixture was stirred during 1.5 h at -10° C. The reaction mixture was washed with water. The organic layer was dried over sodium sulfate, filtered and concentrated under reduced pressure to afford an oil. Flash chromatography on silica gel and elution with a 7:2 mixture of hexane and ethyl acetate afforded the expected compound methyl 2,3,4-tri-O-benzyl-6-O-trifluoromethylsulfonyl -β-D-glucopyranoside (1.408 g, 89%) as an oil, which crystallized in the fridge.
