General procedure for the synthesis of ethyl 3-bromo-4-aminobenzoate from ethyl 4-aminobenzoate: ethyl 4-aminobenzoate (10 g, 61 mmol) was dissolved in DMF (150 mL) under cooling conditions in an ice bath. Subsequently, N-bromosuccinimide (NBS, 10.8 g, 61 mmol) was added in batches and stirred continuously at the same temperature for 30 min. Upon completion of the reaction, the ice bath was removed and the reaction mixture was allowed to continue stirring at room temperature overnight (~18 hours). The reaction mixture was poured into water (500 mL) and the precipitate was collected by filtration. The resulting orange solid was washed with water (50 mL x 2) and recrystallized by ethanol to give the light yellow crystalline product ethyl 3-bromo-4-aminobenzoate (13.3 g, 91% yield). The product was detected by thin layer chromatography (TLC) with an Rf value of 0.38 (Expander ratio: petroleum ether:ethyl acetate=5:1). The melting point was 86-88°C. 1H-NMR (CDCl3, 300MHz) δ: 8.07 (s, 1H), 7.79 (t, J = 11.55Hz, 1H), 6.70 (d, J = 8.10Hz, 1H), 4.58 (br, 2H), 4.37 (dd, J = 6.6Hz, J = 6.6Hz, 2H), 1.34 ( t, J = 7.2 Hz, 3H).
