Under ice-cooling, triethylamine (0.46 ml) and methanesulfonyl chloride (217 μl, 2.80 mmol) were added to dichloromethane (10 ml) solution of 4-(R)-[1-hydroxy-1-phenylmethyl]-1-[1-(R)-phenylethyl]-2-pyrrolidone [F1] (738 mg, 2.50 mmol), and the mixture was stirred at the same temperature for 1 hour. The reaction solution was mixed with 10% citric acid (20 ml) under ice-cooling and extracted with chloroform (30 ml×2). The organic layer was washed with saturated brine (100 ml) and then dried over anhydrous sodium sulfate. The solvent was evaporated under a reduced pressure, and the resulting residue was dissolved in N,N-dimethylformamide (10 ml), mixed with sodium azide (488 mg, 7.50 mmol) and then heated at 60° C. for 1.5 hours. After spontaneous cooling, the reaction solution was mixed with water (50 ml) and extracted with ethyl acetate (70 ml×3), and the organic layer was washed with saturated brine (150 ml) and then dried over anhydrous sodium sulfate. The solvent was evaporated under a reduced pressure and the resulting residue was applied to a silica gel column chromatography. By eluting with n-hexane:ethyl acetate (3:2), 701 mg (87%) of the title compound was obtained as a colorless oil.
