6-Methoxy-1,5-naphthyridin-4-ol (21.5 g) was dissolved in DMF (150 mL) under nitrogen protection and stirred at 0 °C. Phosphorus tribromide (13.5 mL) was slowly added dropwise, and after the dropwise addition was completed, the reaction mixture was gradually warmed up to room temperature, and the reaction was continued to be stirred for 90 min. Upon completion of the reaction, the reaction was quenched by the addition of water (375 mL) and the pH was adjusted with solid sodium carbonate to 7. The precipitated solid product was collected by diafiltration and dried by suction with a sintered funnel for 2 h, followed by drying under vacuum at 45 °C to afford the target compound 8-bromo-2-methoxy-1,5-naphthyridine (26.0 g, 90% yield). The product was characterized by 1H-NMR (DMSO-d6) with the following chemical shifts (δ, ppm): 8.59 (d, 1H), 8.30 (d, 1H), 8.08 (d, 1H), 7.33 (d, 1H), 4.06 (s, 3H).
