Ethyl-4-amino-1-tert-butoxycarbonyl-1,2,5,6-tetrahydropyridine-3-carboxylate (23.6 g) was dissolved in methylene chloride (460 ml), and pyridine (13 ml) and phenyl chlorocarbonate (15 ml) were added under ice cooling and the resultant mixture was stirred for one hour at the same temperature. To the reaction solution, water was added and the mixture was extracted with methylene chloride. After the organic layer was washed sequentially with 1 N hydrochloric acid and saturated saline solution in this order, the organic layer was dried over sodium sulfate, filtrated and concentrated under reduced pressure. To the resultant residue, diethyl ether was added to obtain a precipitate by filtration. The titled compound (10.57 g) was obtained as a colorless solid substance. Furthermore, the filtrate was concentrated under reduced pressure. Thereafter, the resultant residue was purified by medium-pressure silica gel column (solvent; ethyl acetate:hexane=10:90 to 50:50). The resultant crude crystal was washed with a solvent mixture of diethyl ether-hexane to obtain the titled compound (11.10 g) as a slightly yellow solid substance.
