Synthesis of benzoxazole-5-carboxylic acid: 3-amino-4-hydroxybenzoic acid (500 mg, 3.26 mmol) was mixed with trimethyl orthoformate (5 mL) under argon protection and the reaction was heated at 65°C for 2 hours. After completion of the reaction, the mixture was cooled to room temperature, filtered and washed with hexane. The filtrate was concentrated in vacuum to give a white solid product benzoxazole-5-carboxylic acid (78 mg, 15% yield). The product was characterized by the following data: 1H NMR (500 MHz, CDCl3): δ 8.57 (d, J = 1.5 Hz, 1H), 8.20 (dd, J = 8.4, 1.8 Hz, 1H), 8.20 (s, 1H), 7.67 (d, J = 9.0 Hz, 1H). Mass spectrum (MS): m/z 164 (M + H).
