General procedure for the synthesis of 6-amino-3H-quinazolin-4-one from 4-hydroxy-6-nitroquinazoline: a methanol (500 ml) solution of intermediate 5A (1 g, 5.23 mmol) was added to a 1 L three-necked flask to form a yellow suspension. Subsequently 10% palladium/carbon catalyst (0.056 g, 0.523 mmol) was added. The reaction mixture was stirred at room temperature and reacted for 4 hours under hydrogen balloon atmosphere. Upon completion of the reaction, the catalyst was removed by filtration and the filtrate was concentrated to give 0.84 g of yellow solid product (100% yield). The structure of the product was confirmed by 1H NMR (500 MHz, DMSO-d6) with chemical shifts δppm of 5.60 (s, 2H), 7.05 (dd, J = 8.80,2.75Hz, 1H), 7.16 (d, J = 2.75Hz, 1H), 7.36 (d, J = 8.80Hz, 1H), 7.74 (s, 1H ) and 11.80 (s, 1H).
