2-aMino-4,6-diMethoxybenzaMide

21577-57-1

63920-73-0

General procedure for the synthesis of 2-amino-4,6-dimethoxybenzamide from 2-amino-4,6-dimethoxybenzoic acid: first, 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 into the solution over 45 min. After keeping the reaction at 10°C for 45 minutes, the mixture was filtered, washed with isopropyl acetate (4L) and dried under high vacuum at 45°C overnight to obtain the hydrochloride salt (242.3 g, 98% yield) as a white solid. Next, the above hydrochloride (20 g, 0.105 mol) was mixed with oxalyl chloride (33 mL) in a three-necked flask equipped with a reflux condenser and heated with stirring at an external temperature of 170 °C 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, and then the reaction mixture was heated to reflux for 45 min, filtered while hot, and washed with methanol (80 mL) to afford 4,6-dimethoxyisatin (17.2 g, 79% yield) as a yellow-green solid. Subsequently, 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 an external temperature of 70 °C 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, the foamed reaction mixture was continued to be stirred at 70 °C for 2 hours, then cooled to room temperature and stirred overnight. Heated again to 70 °C, additional H2O2 (75 mL) was added and stirring was continued at 70 °C for 2 hours until the reaction was complete. After cooling to 10°C (bath temperature), saturated aqueous Na2S2O3 solution (150 mL) was added. The pH of the mixture was adjusted to 6 with 37% HCl (1.6 L) and glacial acetic acid (75 mL), taking care to keep the temperature of the reaction mixture from exceeding 40°C. The reaction mixture was filtered and washed with water (4 L) to obtain the target amino acid (83.7 g, 55% yield) as a brown solid. Next, the amino acid (82.7 g, 0.42 mol) was dissolved in anhydrous THF (4.2 L), and EDCI (89.2 g, 0.48 mol), HOBT (65 g, 0.48 mmol) and NMM (51.3 mL) were added, and stirred for 3 hours at room temperature. Then 50% aqueous NH3 solution (83 mL) was added and stirring was continued for 16 hours at room temperature. Water (1.25 L) was added and the mixture was extracted with DCM (2 x 250 mL). The organic phases were combined and washed with water (2 x 500mL). After concentration, a slurry was made with ether (550 mL), filtered and dried under high vacuum to give 2-amino-4,6-dimethoxybenzamide (46.7 g, 57% yield) as a brown solid. Finally, 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 mixed in DMF (20 mL) and heated at 80 °C for 12 hour. After cooling to room temperature, it was poured into crushed ice. The solid was collected and purified by column chromatography to afford 2-(4-hydroxy-3,5-dimethylphenyl)-5,7-dimethoxyquinazolin-4(3H)-one (0.9 g, 51% yield) as a white solid. Melting point: 291-293°C.