(Step 2) To ethyl 4-hydroxy-1-methyl-6-oxo-1,6-dihydropyridine-3-carboxylate (9.2 g, 47 mmol) obtained in Step 1 was added phosphorous trichloride (26.1 mL, 280 mmol) and triethylamine (6.5 mL, 47 mmol). The reaction mixture was stirred at 50 °C for 3 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the solvent was removed by evaporation under reduced pressure. Saturated aqueous sodium bicarbonate (100 mL) was added to the residue, which was subsequently extracted with ethyl acetate (3 × 50 mL). The organic layers were combined, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford ethyl 4-chloro-1-methyl-6-oxo-1,6-dihydropyridine-3-carboxylate (6.0 g, 60% yield). The product was confirmed by electrospray ionization mass spectrometry (ESIMS), m/z: 216 (M + H)+.
