The general procedure for the synthesis of ethyl 4-hydroxy-6-methyl-2-oxo-1,2-dihydropyridine-3-carboxylate from ethyl 3-aminocrotonate and diethyl malonate was as follows: ethyl 3-aminocrotonate (100 g, 0.7752 mol) was added to a reactor, followed by the addition of sodium ethoxide (65 g, 0.9559 mol) and anhydrous ethanol (240 g). The reaction system was slowly heated to 80-90 °C, kept at reflux, and the reaction was stirred at this temperature for 24 hours. Upon completion of the reaction, the system was cooled to 50-60 °C and concentrated under reduced pressure to remove about 100 g of ethanol. The concentrated solution was slowly poured into 1000 ml of water, 10 g of basic activated carbon was added, stirred for 1 hour and filtered. The filtrate was cooled to below 0°C and the pH was adjusted to 2 to 3 with ammonium chloride, at which time a large amount of solid precipitated, and the solid was collected by filtration. The resulting solid was dried at 50 to 60°C to give white needle-like crystals of ethyl 2,4-dihydroxy-6-methyl-nicotinate in a yield of 125 g (yield = 81.85%, HPLC purity = 99.5%).
