General procedure for the synthesis of 2-chloro-3-iodopyridine from 2-chloropyridine: 2,2,6,6-tetramethylpiperidine (17 mL, 14 g, 0.1 mol) and 2-chloropyridine (9.5 mL, 11.5 g, 0.1 mol) were sequentially added to a hexane solution of 1.6 M n-butyllithium (62.5 mL, 0.1 mol) at -78 °C with a solvent of 150 mL of tetrahydrofuran. After maintaining the reaction temperature at -78 °C with stirring for 2 h, a tetrahydrofuran solution (50 mL) of iodine (25.5 g, 0.1 mol) was added dropwise to the reaction mixture and stirring was continued for 30 min. Subsequently, the reaction mixture was partitioned between water (100 mL) and ether (3 x 50 mL). The organic layers were combined, washed with saturated aqueous sodium thiosulfate solution (2 x 50 mL), dried over anhydrous magnesium sulfate, filtered and concentrated in vacuum to give the crude product. The crude product was purified by fast chromatography (eluent: heptane/ethyl acetate, 90/10) to give a yellow solid product in 72% yield (17.3 g). The structure of the product was analyzed by 1H NMR (CDCl3): δ 8.38 (dd, J = 4.6/1.7 Hz, 1H), 8.16 (dd, J = 8.0/0.16 Hz, 1H), 6.96 (dd, J = 8.0/4.6 Hz, 1H); 13C NMR (CDCl3): δ 154.5, 148.9, 148.8, 123.2 , 94.9; MS (EI) m/z 240 (M + 1) confirmed.
