The general procedure for the synthesis of 2-chloro-4-methyl-5-iodopyridine from 2-amino-5-iodo-4-methylpyridine was as follows: to a stirred solution of concentrated hydrochloric acid (233 mL) at 0 °C was added 5-iodo-4-methylpyridin-2-ylamine (25 g, 107 mmol, 1 eq.), followed by sodium nitrite (29.5 g, 427 mmol, 4 eq.), which had been pre-dissolved in water (100 mL). 427 mmol, 4 eq.), and the titration process was controlled to be completed within 30 min. The reaction mixture was stirred at room temperature for 16 hours. After confirming complete consumption of the feedstock by TLC monitoring, the reaction mixture was cooled to 0 °C and the pH was adjusted to 12 with saturated aqueous sodium hydroxide solution. the reaction mixture was extracted with dichloromethane (3 x 200 mL). The organic layers were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to give a brown oily crude product (23 g). The crude product was purified by column chromatography on silica gel (100-200 mesh) using a hexane solution of 4% ethyl acetate as eluent.The fraction containing the target compound was collected and concentrated under reduced pressure to give 2-chloro-4-methyl-5-iodopyridine as a brown oil (8 g, 30% yield). The product was confirmed by 1H NMR (400 MHz, CDCl3): δ 2.38 (s, 3H), 7.21 (s, 1H), 8.59 (s, 1H).LC-MS (m/z): 253.7 (M + H).
