The general procedure for the synthesis of 2-chloro-1,6-naphthyridine from 1,6-naphthyridin-2(1H)-one was as follows: 1,6-naphthyridin-2(1H)-one (2 g, 13.68 mmol) was dissolved in phosphorus trichloride (20 mL) and the reaction was carried out at reflux for 16 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the reaction solution was subsequently concentrated under reduced pressure. The concentrated residue was dissolved in dichloromethane (100 mL) and washed with saturated aqueous sodium bicarbonate (100 mL). The organic layer was dried with anhydrous sodium sulfate, filtered and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography with the eluent being a dichloromethane solution containing 1-2% methanol to give 2-chloro-1,6-naphthyridine as a yellow solid. The product was identified by mass spectrometry (ESI, m/z) as 165.0 [M + 1]+; 1H NMR (300 MHz, DMSO-d6) δ 9.43 (s, 1H), 8.83 (d, J = 6.0 Hz, 1H), 8.69 (d, J = 11.7 Hz, 1H), 7.88 (d, J = 5.7 Hz, 1H), 7.86 (d, J = 9.6Hz, 1H).
