A solution of 2-tert-butoxycarbonylamino-4-methylpyridine (20 g, 97 mmol) in anhydrous tetrahydrofuran (300 mL) was cooled to −78° C. and a solution of 1.6 M n-butyllithium in hexane (140 mL, 0.22 mol) was added dropwise with stirring. After complete addition, the mixture was stirred at room temperature for 30 minutes. And then, the mixture was cooled to −78° C. A solution of N-(4-methoxybenzoyl)propyleneimine in anhydrous tetrahydrofuran (50 mL) was added dropwise to the mixture. After complete addition, the mixture was stirred at room temperature for 2 hours. Water (100 mL) and diisopropyl ether (300 mL) were added to the reaction mixture and the resulting crude crystals were collected by filtration. The crude crystals were recrystallized from tetrahydrofuran-hexane to obtain 23 g of the title compound (67 mmol, yield 69%).
