Step B: Preparation of 2,4,7-trichloroquinazoline. 7-Chloro-1H-quinazoline-2,4-dione (2.0 g, 10 mmol) was suspended in acetonitrile (ACN, 50 mL), followed by the addition of phosphorus oxychloride (POCl3, 5.0 mL, 55 mmol) and diisopropylethylamine (DIEA, 5.0 mL, 28 mmol). The reaction mixture was heated to reflux for 36 hours. Upon completion of the reaction, it was cooled to room temperature and concentrated under reduced pressure. The residue was carefully quenched with ice water and sodium bicarbonate solution. The resulting solid product was collected by filtration and dried. Finally, purification by column chromatography (eluent: ethyl acetate/hexane, 0:100 to 10:90) afforded the target compound 2,4,7-trichloroquinazoline (2.1 g, 89% yield). The mass spectrometry (MS) and nuclear magnetic resonance (NMR) data were consistent with those reported in the literature (Bioorganic and Medicinal Chemistry, 2003, 11, 2439-2444).1H NMR (400 MHz, DMSO-d6) δ: 8.32 (d, J = 8.7 Hz, 1H), 8.20 (d, J = 1.9 Hz, 1H), 7.93 (dd, J = 9.0, 2.1 Hz, 1H).
