Acetic Anhydride → 1,2,3,4,6-penta-O-acetyl-L-mannopyranose

L-(−)-mannose (9.0 g, 49.96 mmol) was dissolved in pyridine (120 ml), and the resulting solution was cooled in ice. Acetic anhydride (60 ml) was added dropwise thereto over about 15 minutes. The resulting solution was stirred overnight while gradually returning to room temperature. Thereafter, the reaction mixture was concentrated under reduced pressure. Toluene was added to the resulting residue, and an azeotropic distillation procedure was performed twice. Ethyl acetate was added to the residue to dissolve the residue, and the resulting solution was washed sequentially with saturated NaHCO3 solution, water, and saturated saline. The organic layer was dried over anhydrous magnesium sulfate and filtered, and the filtrate was concentrated under reduced pressure. The obtained residue was dried well under reduced pressure, whereby a target product was obtained (crude yield: 21.04 g (which exceeded the theoretical yield because ethyl acetate and the like were contained, and therefore, the molar amount thereof was taken as 49.96 mmol, and the subsequent reaction was performed)).