7-Chloro-1,6-diazanaphthalen-4(1H)-one (340 mg, 1.89 mmol) was used as starting material and dissolved in 1,2-dichloroethane. Under stirring conditions, N,N-diisopropylethylamine (DIEA, 653 μL, 3.95 mmol) and phosphorochloridic acid (345 μL, 3.78 mmol) were added sequentially. The reaction mixture was stirred at 70 °C for 30 min. After completion of the reaction, the mixture was cooled to room temperature and slowly poured into ice water. The pH was adjusted to 8 with 2N NaOH solution and subsequently extracted with ethyl acetate (EA). The organic phase was washed with saturated ammonium chloride (NH4Cl) solution and dried with anhydrous sodium sulfate (Na2SO4). The solvent was removed by concentration under reduced pressure and the resulting residue was purified by column chromatography to afford the target product 4,7-dichloro-1,6-naphthyridine in 94% yield. The structure of the product was confirmed by 1H NMR (300 MHz, DMSO-d6): δ 9.47 (d, J = 0.6 Hz, 1H), 9.10 (d, J = 4.7 Hz, 1H), 8.18 (s, 1H), 7.94 (dd, J = 4.8 Hz, 1H).
