General procedure for the synthesis of 4-bromo-5-chloro-2-methoxyaniline from 4-chloro-2-aminoanisole: N-bromosuccinimide (86.7 g, 0.487 mol) was added in batches to a solution of 5-chloro-2-methoxyaniline (Intermediate 5, 76.7 g, 0.487 mol) in acetonitrile (500 mL) at 0 °C, and the addition process lasted for 2 hours. After completion of the addition, the solvent was removed by distillation under reduced pressure. The residue was purified by column chromatography (silica gel: 200-300 mesh, 200 g) with petroleum ether/ethyl acetate as eluent (ratio tapered from 20:1 to 4:1) to afford 4-bromo-5-chloro-2-methoxyaniline as a light yellow solid (40.2 g, 35% yield). The product was analyzed by LCMS (A): retention time (Rt) 1.63 min, molecular ion peak (MH+) m/z 236/238. 1H NMR (300 MHz, CDCl3) δ 6.93 (s, 1H), 6.78 (s, 1H), 3.83 (s, 3H).
