General procedure for the synthesis of 2-phenylnaphtho[2,3-D]oxazole-4,9-dione from 2-amino-3-hydroxynaphthalene-1,4-dione and trimethyl orthobenzoate: 2-amino-3-hydroxynaphthalene-1,4-dione (500 mg, 1.0 eq.), trimethyl orthobenzoate (3.6 mL, 8.0 eq.) and pyridinium p-toluenesulfonate (PPTS, 66 mg , 0.1 eq.) were mixed and the reaction was heated in a 90 °C oil bath for 2 hours. After confirming complete consumption of the raw materials by LC-MS analysis, the reaction mixture was diluted with ether (Et2O) and the resulting yellow precipitate was collected. The precipitate was washed sequentially with ether and ethyl acetate (EtOAc) and dried to afford the target product 2-phenylnaphtho[2,3-D]oxazole-4,9-dione (472 mg, 65% yield) as a bright yellow fluffy solid. The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3) and LRMS (M + H)+: 276.19. 1H NMR data were as follows: δ 7.53-7.62 (3H, m), 7.81 (2H, dd, J = 3.5, 5.9 Hz), 8.25 (1H, dd, J = 3.3, 5.7 Hz), 8.29 (1H , dd, J = 3.1, 5.9 Hz), 8.31-8.34 (2H, m).
