Ethyl-4-phenoxycarbonylamino-1-tert-butoxycarbonyl-1,2,5,6-tetrahydropyridine-3-carboxylate (5.0 g) was dissolved in THF (50 ml), and propargylamine (1.32 ml) and 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) (0.2 ml) were added and the resultant mixture was stirred at room temperature for 2 hours. After production of an intermediate (urea) was confirmed by TLC, a 5 N aqueous sodium hydroxide solution (5 ml) was added and the resultant mixture was further stirred at room temperature for 2 hours. To the reaction solution, 6 N hydrochloric acid was added to neutralize and the resultant mixture was then concentrated. To the residue, water was added and the mixture was extracted with ethyl acetate. After the organic layer was washed with a saturated saline solution, the organic layer was dried over sodium sulfate, filtrated and concentrated under reduced pressure. A precipitate was obtained by filtration. The titled compound (3.78 g) was obtained as a white powder.
