General procedure for the synthesis of 2-(2-hydroxyphenyl)-4H-benzo[E][1,3]oxazin-4-one from 2-hydroxy-N-(2-hydroxybenzoyl)benzamide: Toluene (1,400 mL) and 10.5 g of p-toluenesulfonic acid monohydrate were added to 140 g of the synthesis intermediate mA, and the reaction mixture was stirred and reacted for 6 hours at 150 °C. Upon completion of the reaction, the mixture was cooled to 60 °C, followed by the addition of 14 mL of triethylamine to the reaction solution and continued cooling to room temperature. The resulting solid was collected by filtration and washed with distilled water to yield 122 g of the synthesized intermediate mB in 94% yield.
