General procedure for the synthesis of 7-bromoquinazoline-2,4(1H,3H)-dione from methyl 2-amino-4-bromobenzoate and sodium cyanate: firstly, 87.0 g (1.33 mol) of sodium cyanate was added to 1.2 liters of acetic acid solution containing 269.0 g (1.17 mol) of methyl 2-amino-4-bromobenzoate and stirred at room temperature. Subsequently, the reaction mixture was continued to be stirred for 22 hours. Upon completion of the reaction, the reaction mixture was diluted with 1.5 liters of water and the solid residue was isolated by diafiltration. Next, 0.42 liters of 32% sodium hydroxide solution was added to the resulting solid and the mixture was diluted with 3.5 liters of water and subsequently heated on a steam bath for 4 hours. The reaction mixture was cooled and the solid residue was again separated by diafiltration. After conventional post-processing, 205.2 g of 7-bromo-1H-benzo[d]-1,3-oxazine-2,4-dione was finally obtained as a solid, which showed (M + H)+ = 243 by HPLC/MS.
