Methyl 4-butoxy-2-oxo-3-butenoate (37 g, 200 mmol) and guanidine hydrochloride (23 g, 240 mmol) were suspended in propionitrile (50 mL) and triethylamine (29 mL, 210 mmol) was added. The reaction mixture was stirred at 100 °C for 4 hours. Upon completion of the reaction, the reaction mixture was concentrated under reduced pressure and the residue was purified by silica gel column chromatography to afford 18 g of methyl 2-aminopyrimidine-4-carboxylate and its mixture in the form of butyl ester as an off-white solid (yield: 60%). The product was characterized by 1H-NMR (500 MHz, DMSO-d6): δ 3.85 (s, 3H), 6.99-7.06 (m, 3H), 8.48 (d, J = 4.8 Hz, 1H).
