General procedure for the synthesis of 3-bromo-1,5-naphthyridine from 1,5-naphthyridine: To a 10 mL solution of glacial acetic acid containing compound 4 (2.7 g, 20.76 mmol) and NaOAc (3.41 g, 41.52 mmol), stirred at 85 °C, 1 M of bromine in acetic acid (35 mL) was slowly added, and the reaction lasted for 5 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the acetic acid was removed by vacuum concentration. The product was purified by column chromatography (petroleum ether/ethyl acetate = 2:1) to give compound 5 (2.36 g, 55% yield) as a white solid. Melting point: 107-108 °C (literature value: 108-109 °C).1H NMR (400 MHz, CDCl3): δ 8.96 (d, J = 2.1 Hz, 2H), 8.56 (s, 1H), 8.36 (d, J = 8.5 Hz, 1H), 7.69-7.56 (m, 1H).
