Step b Synthesis of 4-chloro-6,7-dimethoxy-2-methylquinazoline: 6,7-dimethoxy-2-methylquinazolin-4(3H)-one (1.0 g) was mixed with phosphorus trichloride (20 mL) and heated to reflux for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, slowly poured into ice water and stirred for 10 min. The aqueous phase was extracted with chloroform (3 x 100 mL), the organic phases were combined, washed sequentially with water and saturated saline, and dried over anhydrous sodium sulfate. The desiccant was removed by filtration and the filtrate was concentrated under reduced pressure to give the yellow solid product 4-chloro-6,7-dimethoxy-2-methylquinazoline (1.0 g, 92% yield) with a melting point of 182-184 °C. 1H NMR (400 MHz, CDCl3): δ 7.36 (1H, s), 7.30 (1H, s), 4.06 (6H, s), 2.81 (3H, s); LC-MS (positive ion mode): m/z 239, 241 [M+H]+.
