General procedure for the synthesis of 6-nitrobenzo[d]oxazole: To a stirred solution of 2-amino-5-nitrophenol (0.5 g, 1 eq.) in triethyl orthoformate (2.7 mL, 5 eq.) was added p-toluenesulfonic acid monohydrate (0.031 g, 0.5 eq.). The reaction mixture was heated at 80 °C for 1 hour. Upon completion of the reaction, the mixture was cooled to 0 °C and the precipitate formed was collected by filtration. The precipitate was washed sequentially with ice-cold ether and water. Finally, the solid product was dried under vacuum to afford 6-nitrobenzo[d]oxazole (0.38 g, 72% yield). The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 9.12 (s, 1H), 8.79 (s, 1H), 8.34 (d, J = 8.40 Hz, 1H), 8.07 (d, J = 8.80 Hz, 1H).
