Triethylamine → Methyl [(5-chloropyridin-2-yl)amino](oxo)acetate

2-Amino-5-chloropyridine (1.16 g) and triethylamine (1.51 ml) were dissolved in methylene chloride (26 ml), ethyl chlorooxoacetate (1.10 ml) was added to the solution under ice cooling, and the mixture was stirred at room temperature for 14 hours. After a saturated aqueous solution of sodium hydrogencarbonate was added to the reaction mixture to conduct liquid separation, the resultant organic layer was dried over anhydrous sodium sulfate, and the solvent was distilled off under reduced pressure. The residue was purified by column chromatography on silica gel (hexane:ethyl acetate=3:1). The thus-obtained pale yellow solids were dissolved in methanol (20 ml), and the solution was stirred at 50° C. for 11 hours. The reaction mixture was concentrated under reduced pressure, and crystals deposited were collected by filtration and dried to obtain the title compound (0.43 g).