General procedure for the synthesis of 3-bromo-5-iodopyridine from 3,5-dibromopyridine: 3,5-dibromopyridine (0.52 g, 2.19 mmol) was dissolved in anhydrous tetrahydrofuran (4 mL) at -10 °C, keeping the internal temperature below -5 °C. Subsequently, tetrahydrofuran solution of 2M isopropylmagnesium chloride (0.25 g, 2.11 mmol) and anhydrous tetrahydrofuran solution of iodine (0.62 g, 2.11 mmol) were added sequentially and slowly and stirred for about 5 minutes. After completion of the reaction, the reaction mixture was diluted with ethyl acetate and saturated aqueous sodium bisulfite. The organic layer was separated, dried over magnesium sulfate, filtered and concentrated to afford 3-bromo-5-iodopyridine (4.85 g, 98% yield), which can be used directly for further purification. The product characterization data were as follows: 1H NMR (400 MHz, CDCl3) δ 7.54-7.51 (m, 1H), 8.26 (s, 1H), 8.42 (s, 1H); MS (ES): m/z = 284 [M + H]+.
