Example 1 Step a: Synthesis of 2-bromo-4-fluoro-6-methylaniline
N-Bromosuccinimide (18.7 g, 0.105 mol) was dissolved in 70 mL of N,N-dimethylformamide, and the solution was added slowly and dropwise to a solution containing 4-fluoro-2-methylaniline (dissolved in 70 mL of N,N-dimethylformamide) at a reaction temperature of 20 °C. The reaction mixture was stirred overnight. The dark colored reaction solution was poured into a mixture consisting of water (1000 mL), brine (50 mL) and ethyl acetate (300 mL). The mixture was transferred to a dispensing funnel, shaken well and separated. The aqueous phase was extracted with ethyl acetate (4 x 150 mL). The organic layers were combined, washed sequentially with water (5 x 100 mL) and brine (2 x 100 mL), dried over anhydrous sodium sulfate, filtered and concentrated. The purity of the raw material was shown to be ≥95% by 1H NMR analysis. The product was further purified by silica gel column chromatography (elution system: ethyl acetate/hexane, 1:8). The pure fractions were combined and evaporated to give 14.9 g of product. The impure fractions were combined, concentrated and redissolved in ether (30 mL) and extracted with 5% hydrochloric acid (5 x 10 mL). The acidic aqueous phase was alkalized with aqueous potassium hydroxide and then extracted with ether to give 0.8 g of the target compound. The total yield was 15.7 g (77% yield).
1H NMR (400 MHz, DMSO-d6) δ ppm: 7.16 (dd, 3JH-F = 8.3 Hz, 4JH-H = 2.9 Hz, 1H, Ar), 6.91 (dd, 3JH-F = 9.3 Hz, 4JH-H = 2.9 Hz, 1H, Ar), 4.83 (br.s, 2H, NH2), 2.16 (s 3H, CH3).
