21038-67-5

908240-50-6

To a mixture of pyrido[3,4-d]pyrimidine-2,4(1H,3H)-dione (2b, 20.00 g, 122.60 mmol) and phosphorus oxychloride (POCl3, 328.03 g, 2.14 mol) in toluene (200 mL) was added dropwise N,N-diisopropylethylamine (DIEA, 31.69 g, 245.20 mmol ). The reaction mixture was stirred at 25 °C for 18 h to obtain a suspension. Upon completion of the reaction, the solvent and unreacted phosphorous trichloride were removed by distillation under reduced pressure. The residue was diluted with dichloromethane (DCM, 50 mL) and neutralized with DIEA to pH=7 at -20 °C. After concentration again, the residue was purified by silica gel column chromatography (eluent: 20-50% ethyl acetate/petroleum ether) to afford the target product 2,4-dichloropyrido[3,4-d]pyrimidine (2c, 20.00 g, 99.99 mmol, 82% yield) as a yellow solid. ), as a yellow solid. The product was confirmed by 1H NMR (400 MHz, CDCl3): δ 9.52 (s, 1H), 8.92 (d, J=5.6 Hz, 1H), 8.04 (d, J=5.6 Hz, 1H). the LCMS analysis showed m/z [M+H]+ of 200.0.