1,2,4,6-Tetra-O-acetyl-3-deoxy-3-[4-(methoxycarbonyl)-1H-1,2,3-triazol-1-yl]-D-galactopyranose 23 (33 mg, 0.072 mmol) was dissolved in dichloromethane (1 ml) which had been dried over 4 Å molecular sieves. Acetic anhydride (14 l, 0.20 mmol) and HBr (0.2 ml of a 33% solution in AcOH) were added, and the mixture was stirred under N2 at room temperature. After 3 h 15 min, the reaction mixture was diluted with dichloromethane (30 ml) and poured into ice-water (30 ml). The organic phase was washed with NaHCO3 (30 ml of a saturated aqueous solution), dried (MgSO4), filtered and concentrated in vacuo. The residue was purified by flash column chromatography to give 24 (16 mg, 46%), which was used immediately in the synthesis of 25.
