(Step 2) Synthesis of 2,4-dichloro-6-fluoroquinazoline: Phosphorus pentachloride (12.5 g, 60.0 mmol) was added to phosphorus trichloride (46.0 mL, 502.5 mmol), followed by the slow addition of 6-fluoroquinazoline-2,4(1H,3H)-dione (3.6 g, 20.0 mmol) under stirring. The reaction mixture was heated to reflux and stirred for 9 hours. After completion of the reaction, the mixture was cooled and the solvent was removed under vacuum. An ice-water mixture (400 mL) was added to the residue and stirring was continued for 0.5 hours. The mixture was extracted with dichloromethane (DCM, 250 mL x 3). The DCM layers were combined, dried with anhydrous sodium sulfate, filtered, and the filtrate was concentrated under vacuum. The residue was purified by silica gel column chromatography (eluent: petroleum ether/ethyl acetate, v/v=30/1) to afford the title compound 2,4-dichloro-6-fluoroquinazoline as a white solid (3.735 g, 86.0% yield). m/z MS (ESI, cationic): 216.9 [M + H]+; 1H NMR (CDCl3, 400 MHz) δ ( ppm): 8.03 (dd, J=9.2 Hz, 4.9 Hz, 1H), 7.86 (dd, J=8.1 Hz, 2.7 Hz, 1H), 7.79-7.73 (m, 1H).
