GENERAL METHOD: Sodium metal (12.9 g, 0.56 mol) was dissolved in anhydrous ethanol (300 mL) under argon protection while stirring vigorously using a mechanical stirrer. The reaction flask was equipped with a reflux condenser with a calcium chloride drying tube. After all the sodium was completely dissolved, the reaction mixture was cooled to room temperature. Guanidine hydrochloride (21.02 g, 0.22 mol) and monosubstituted diethyl malonate (0.2 mol) were added sequentially under continuous vigorous stirring. Stirring became difficult after 2 h of continued vigorous stirring due to the large amount of solid products produced during the reaction. Subsequently, anhydrous ethanol (200 mL) was added and the reaction mixture was refluxed for 1 hour while stirring was maintained. Upon completion of the reaction, a portion of the ethanol (about 200-300 mL) was evaporated under reduced pressure using a rotary evaporator, and then water (500 mL) was added to the reaction mixture. After stirring, the product was almost completely dissolved in the form of sodium salt. Next, the reaction mixture was neutralized by dropwise addition of acetic acid, resulting in immediate quantitative precipitation of the target product 2-amino-5-ethyl-6-hydroxypyrimidin-4(3H)-one as a fine solid. The mixture was heated under reflux conditions for 10 minutes and then cooled to room temperature. This heating and cooling process was repeated twice to obtain a solid product that could be easily filtered. The solid was collected by filtration and washed sequentially with water (2 x 50 mL), ethanol (2 x 50 mL) and acetone (2 x 50 mL). Finally, the product was dried under high vacuum at 60 °C for 2 days. The resulting product was pure enough to be used in subsequent reactions and was analyzed to contain only water of crystallization.
