Methyl (2S,4R)-4-amino-1-tert-butoxycarbonylpyrrolidine-2-carboxylate [product of Reference Example 4(2), 3.32 g] and triethylamine (1.4 mL) were dissolved in tetrahydrofuran (20 mL). 2-Chlorobenzoxazole (0.86 mL) was added thereto and the mixture was stirred at room temperature for 48 hr. The reaction mixture was added to water and extracted with ethyl acetate. The extract was washed with saturated aqueous sodium hydrogencarbonate solution and brine, and dried. The solvent was evaporated under reduced pressure and the residue was purified by silica gel chromatography to give methyl (2S,4R)-4-(2-benzoxazolyl)amino-1-tert-butoxycarbonylpyrrolidine-2-carboxylate (1.48 g) as a white solid.
