In 127 ml of ethanol is dissolved 12.7 g of 1-benzyl 2-ethyl (2S,4R)-4-(tetrahydro-2H-pyran-2-yloxy)-1,2-pyrrolidinedicarboxylate. After adding 37.0 ml of 1 mol/L sodium hydroxide solution at 5-10° C., the mixture thus obtained is stirred at ambient temperature for 1.5 hours. The solvent is distilled off from the reaction mixture under reduce pressure, the residue thus obtained is dissolved in 90 ml of N,N-dimethylformamide, 10.9 ml of diphenylphosphoryl azide, 14.1 ml of triethylamine and 3.94 g of N,O-dimethylhydroxylamine hydrochloride are successively added at 5-10° C., and the mixture thus obtained is stirred at ambient temperature for one hour. Ethyl acetate and water are added to the reaction mixture, pH is adjusted to 6.5 with 6 mol/L hydrochloric acid, and the organic layer is separated. The organic layer is washed with water and saturated aqueous solution of sodium chloride successively and dried over anhydrous sodium sulfate, and then the solvent is distilled off under reduced pressure. The residue thus obtained is purified by silica gel column chromatography (eluent; n-hexane:ethyl acetate=4:1) to obtain 3.75 g of benzyl (2S,4R)-2-{[methoxy(methyl)amino]carbonyl}-4-(tetrahydro-2H-pyran-2-yloxy)-1-pyrrolidinecarboxylate as a light yellow oily product.
