Synthesis of 6-amino-2-methoxy-4-pyrimidinone (compound a): was carried out with reference to the method described by W. Pfleiderer (Chem. Ber., 90: 2272 (1957). The steps were as follows: sodium methanol solution was prepared by dissolving sodium metal (15 g, 652 mmol) in 200 mL of methanol in batches. To this solution, O-methylisourea sulfate (30.6 g, 248 mmol) and ethyl cyanoacetate (30 g, 265 mmol) were added sequentially. The reaction mixture was heated to reflux and stirred continuously for 4.5 hours. After completion of the reaction, the mixture was cooled to room temperature, the solid product was collected by filtration and the solid was washed with a small amount of methanol. The filtrate and washings were combined and concentrated to dryness under reduced pressure to give a white solid residue. The residue was dissolved in 300 mL of hot water and the pH of the solution was adjusted with acetic acid to 7. Subsequently, the precipitated solid was filtered, washed with water, and dried to give 28 g (80% yield) of the target product, 6-amino-2-methoxy-4-pyrimidinone, as a white solid.
