General procedure for the synthesis of 2,4-dichloro-5-methoxyquinazoline from 5-methoxyquinazoline-2,4(1H,3H)-dione (310 mg, 1.6 mmol): 5-methoxyquinazoline-2,4(1H,3H)-dione was added to a dry flask, followed by phosphorus trichloride (10 mL) and N,N-dimethylaniline (0.2 mL). After the addition was completed, the reaction mixture was heated to reflux for 4 hours. After completion of the reaction, the volatile components were evaporated under reduced pressure to obtain the crude product. Saturated sodium bicarbonate solution was added to the crude product, followed by ethyl acetate for extraction. The organic phase was separated, dried over anhydrous sodium sulfate and filtered. The solvent was again evaporated under reduced pressure to give another crude product. The crude product was purified by silica gel column chromatography with an eluent of 10% to 20% ethyl acetate/hexane mixed solvent, resulting in 2,4-dichloro-5-methoxyquinazoline (180 mg, 49% yield) as a white solid.1H NMR (400 MHz, CDCl3) δppm: 4.03 (s, 3H), 7.02 (d, J=8.35 Hz. 1H), 7.55 (d, J=8.35Hz, 1H), 7.85 (t, J=8.35Hz, 1H).
