General procedure for the synthesis of 4-chloro-6-bromoquinazoline from 6-bromo-3H-quinazolin-4-one (20 g, 89 mmol): 6-bromo-3H-quinazolin-4-one was suspended in 140 mL of phosphorus oxychloride (POCl3), and the reaction was stirred for 3 hr at 140 °C. After completion of the reaction, the reaction mixture was concentrated under vacuum and the residue was dissolved in 500 mL of dichloromethane (CH2Cl2). The reaction solution was neutralized with 200 g of solid sodium bicarbonate (NaHCO3), filtered, and the filtrate was evaporated under vacuum to afford 4-chloro-6-bromoquinazoline (21 g, 95% yield) as a beige solid. The product was characterized by 1H-NMR (400 MHz, CDCl3, 298 K): δ 7.98 (d, 1H), 8.09 (d, 1H), 8.5 (s, 1H), 9.1 (s, 1H). Mass spectrometry (MS) analysis showed [M + 1]+ m/z 243.0-244.9, retention time (Rt) = 1.24 min.
