To a solution of an optically-active compound of 3-amino-3-(2-hydroxyethyl)piperidine-1-carboxylic acid tert-butyl ester (6.46 g), triphenylphosphine (12.5 g) and triethylamine (13.3 ml) in dichloromethane (226 ml) cooled to 0° C. was added carbon tetrabromide (15.8 g). The reaction mixture was stirred at room temperature for 40 minutes and cooled to 0° C. again. Then, thereto were added triethylamine (5.5 ml) and benzyl chloroformate (4.9 ml), and the mixture was stirred for 3.5 hours at room temperature. To the mixture was added water (200 ml), and the mixture was extracted with chloroform (100 ml). The organic layer was washed with saturated aqueous sodium chloride solution, and concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (eluent: n-hexane/ethyl acetate=5/1) to give the titled compound (5.35 g).
