Step 1. Synthesis of 1-bromo-3-chloro-2-iodobenzene: To an anhydrous THF (664 mL) solution containing diisopropylamine (76 mL, 0.4 mol) was slowly added dropwise a n-hexane (220 mL) solution of 2.5 M n-butyllithium (n-BuLi, 160 mL, 0.4 mol) at -78 °C for 1 h under nitrogen protection. The reaction temperature was maintained at -78 °C and stirring was continued for 1 h. A solution of 1-bromo-3-chlorobenzene (76 g, 0.4 mol) in anhydrous THF (300 mL) was added slowly dropwise. After the dropwise addition, the reaction was kept at -78 °C for 1 h. Subsequently, a solution of anhydrous THF (400 mL) with iodine (101 g, 0.4 mol) was added slowly dropwise. The reaction system was gradually warmed to room temperature over 2 hours and stirring was continued at room temperature for 18 hours. After completion of the reaction, the mixture was concentrated under reduced pressure to give the crude product (120 g). The crude product was purified by distillation under reduced pressure to give 1-bromo-3-chloro-2-iodobenzene (115 g, 91% yield). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3) and mass spectrometry (MS): 1H NMR δ 7.12-7.18 (t, 1H), 7.35-7.41 (dd, 1H), 7.49-7.54 (dd, 1H); MS (E/Z): 317 (M+H+).
