tert-Butyl cis(±)-4-amino-3-methoxypiperidine-1-carboxylate obtained by the method described in Example (1e) (3.0 g, 13.0 mmol) was dissolved in THF (60 mL), followed by cooling to 0° C. Thereafter, aqueous sodium carbonate solution (30 mL) and benzyl chloroformate (2.8 mL, 19.6 mmol) were added, and the mixture was stirred for one hour. Ethyl acetate was added to the reaction solution, and the organic layer was washed with brine and dried over anhydrous sodium sulfate. Following concentration under reduced pressure, the residue was purified by silica gel column chromatography (elution solvent: hexane/ethyl acetate=90/10, 50/50) to obtain 4.29 g of the title compound as a pale yellow solid (90%).
