8-Bromoquinazoline-2,4(1H,3H)-dione (12.1 g, 50 mmol, 1 eq.) was used as starting material, which was dissolved in phosphorous trichloride (POCl3, 130 mL), followed by the addition of N,N-dimethylformamide (DMF, 0.5 mL) as catalyst. The reaction mixture was stirred at 130 °C for 12 h. After completion of the reaction, the reaction was cooled to room temperature. The reaction mixture was concentrated by rotary evaporator. The concentrated residue was dissolved in ethyl acetate (EA, 100 mL) and quenched by slowly pouring into ice water under vigorous stirring. The organic phase was separated, washed with saturated saline, dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated again. Finally, the target product 8-bromo-2,4-dichloroquinazoline was purified by column chromatography (eluent: petroleum ether/ethyl acetate = 10:1, v/v) as a yellow solid (9.1 g, 60% yield).
