General procedure for the synthesis of 5-amino-2-bromobenzoic acid from 3-aminobenzoic acid: 3-aminobenzoic acid (3.00 g, 21.9 mmol) was dissolved in N,N-dimethylformamide (18.0 mL) and cooled to below 5 °C. In another vessel, a solution was prepared by mixing N,N-dimethylformamide (9.00 mL) with N-bromosuccinimide (4.09 g, 23.0 mmol). This solution was slowly added to the cooled 3-aminobenzoic acid solution, keeping the reaction temperature at 5 °C or lower. The reaction mixture was stirred at 5 °C for 1 h. After the reaction mixture was stirred for 1 h, water (60.0 mL) was added and the stirring was continued for 12 h at 5 °C. Upon completion of the reaction, the solid product was collected by filtration, and the filtrate was washed with water (5.00 mL) and dried to give 5-amino-2-bromobenzoic acid (3.68 g, 78% yield). The structure of the product was confirmed by 1H-NMR (400 MHz, DMSO-D6): δ 5.49 (s, 2H), 6.59 (dd, J = 8.5,2.9Hz, 1H), 6.93 (d, J = 2.9Hz, 1H), 7.25 (d, J = 8.5Hz, 1H), 13.04 (s, 1H).
