To a solution of (2R)-2-allyloxycarbonylamino-2-methyl-4-[5-(4-cyclohexyloxybut-1-ynyl)furan-2-yl]butan-1-ol (0.6202 g, 1.54 mmol) obtained in Example (26a) in dichloromethane (15 ml) were added successively 1H-tetrazole (0.7220 g, 10.31 mmol) and diallyl diisopropylphosphoramidite (0.81 ml, 3.06 mmol) with stirring under ice-cooling, and then the reaction mixture was stirred at room temperature for 2 hours. After stirring, to the reaction mixture was added m-chloroperbenzoic acid (content: 70%) (0.7556 g, 3.07 mmol) with stirring under ice cooling, and the resulting mixture was stirred at the same temperature for 10 minutes. After stirring, to the reaction mixture was added 10% aqueous sodium thiosulfate solution to quench the reaction, and the resulting mixture was extracted with dichloromethane. The extract was washed successively with saturated aqueous sodium hydrogencarbonate solution and saturated aqueous sodium chloride solution and dried over anhydrous sodium sulfate. After filtration, the solvent was removed in vacuo, and the residue was purified by chromatography on a silica gel column using a mixed solvent of hexane and ethyl acetate (3:2) as the eluent to afford the title compound (0.7049 g, yield: 81%)
