1. 3,5-Dimethoxyaniline (199 g, 1.30 mol) was dissolved in ether (5.0 L) in a 5 L three-necked flask and cooled to 0°C. HCl gas (227 g) was passed over 45 min. After keeping the reaction at 10°C for 45 min, the mixture was filtered, washed with isopropyl acetate (4L) and dried under high vacuum at 45°C overnight to give 3,5-dimethoxyaniline hydrochloride (242.3 g, 98%) as a white solid.
2. The above hydrochloride (20 g, 0.105 mol) was reacted with oxalyl chloride (33 mL) in a 3-necked flask equipped with a reflux condenser, heated to 170 °C (external temperature) with stirring for 2 h, during which oxalyl chloride was distilled from the reaction mixture. The flask was cooled to 0 °C, methanol (40 mL) was added, heated to reflux for 45 min, filtered while hot and washed with methanol (80 mL) to give 4,6-dimethoxyisatin (17.2 g, 79%) as a yellow-green solid.
3. To a 40% aqueous NaOH solution (1.5 L) of indigo red (162 g, 0.78 mol), 35% H2O2 (405 mL) was slowly added at 70 °C (external temperature) for 2 hours. The internal reaction temperature was increased from 64°C to a maximum of 80°C after each addition of H2O2. After addition, stirring was continued at 70 °C for 2 h, then cooled to room temperature overnight. Heat again to 70 °C, add additional H2O2 (75 mL) and continue stirring at 70 °C for 2 hours until the reaction is complete. Cooled to 10 °C (bath temperature), saturated aqueous Na2S2O3 solution (150 mL) was added. The pH was adjusted to 6 with 37% HCl (1.6 L) and glacial acetic acid (75 mL) and the reaction temperature was kept at no more than 40°C. The reaction mixture was filtered and washed with water (4L) to obtain the target amino acid (83.7 g, 55%) as a tan solid.
4. The amino acid (82.7 g, 0.42 mol) was dissolved in anhydrous THF (4.2 L), EDCl (89.2 g, 0.48 mol), HOBT (65 g, 0.48 mol) and NMM (51.3 mL) were added and stirred at room temperature for 3 hours. Add 50% aqueous NH3 solution (83mL) and continue stirring at room temperature for 16 hours. Water (1.25 L) was added and extracted with DCM (2 x 250 mL). The organic phases were combined, washed with water (2 x 500 mL), concentrated, slurried with ether (550 mL), filtered and dried under high vacuum to give 2-amino-4,6-dimethoxybenzamide (46.7 g, 57%) as a brown solid.
5. 2-Amino-4,6-dimethoxybenzamide (1.06 g, 5.4 mmol), 3,5-dimethyl-4-hydroxybenzaldehyde (0.810 g, 5.4 mmol), K2CO3 (0.747 g, 5.4 mmol), and I2 (1.645 g, 6.5 mmol) were dissolved in DMF (20 mL), and heated at 80 °C for 12 hours . Cooled to room temperature, poured into crushed ice, collected the solid and purified by column chromatography to give 2-(4-hydroxy-3,5-dimethylphenyl)-5,7-dimethoxyquinazolin-4(3H)-one (0.9 g, 51%) as a white solid. Melting point: 291-293°C.
