Step 1: 2-Amino-3-fluorobenzoic acid (1.0 g, 6.45 mmol) was dissolved in N,N-dimethylformamide (DMF, 10 mL) at -10 °C. Subsequently, a solution of N-bromosuccinimide (NBS, 1.15 g, 6.45 mmol) in DMF (4 mL) was added dropwise to the above solution over 10 min. After the dropwise addition was completed, the reaction mixture was kept at -10°C and stirring was continued for 1 hour. Upon completion of the reaction, the reaction was quenched with aqueous sodium bisulfate (50 mL), at which point a large amount of solid precipitated. The solid product was collected by filtration and dried under vacuum to give 2-amino-5-bromo-3-fluorobenzoic acid (1.2 g, yield: 80%) as a yellow solid.
