To a solution of (1S,2S,3S,4R,5S)-3,4-dibenzyloxy-5-[4-chloro-3-[(4-ethoxyphenyl)methyl]phenyl]-1-(hydroxymethyl)-6,8-dioxabicyclo[3.2.1]octan-2-ol 28d (11.68 g, 18.9 mmol) in dichloromethane (40 mL) were added tert-butyldimethylsilyl chloride (3.4 g, 22.68 mmol), imidazole (2.57 g, 37.8 mmol) and a catalytic amount of 4-dimethylaminopyridine in turn at 0° C. The mixture was stirred at room temperature for 30 min and adjusted with saturated aqueous sodium bicarnonate till pH becomes 7. The resulting mixture was extracted with dichloromethane (50 mL×3). The combined organic phases were washed with saturated aqueous sodium chloride (30 mL×2), dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated in vacuo to give the title compound 28e as a white solid (15.9 g, 100%). The crude product was used for next step without further purification.
