Synthesis
General procedure for the synthesis of 2-chloro-5-iodo-6-methylpyridine from 2-amino-5-iodo-6-methylpyridine: 5-iodo-6-methylpyridin-2-ylamine (25 g, 107 mmol, 1 equiv.) was added to a stirred solution of concentrated hydrochloric acid (233 mL) at 0 °C, followed by a slow, dropwise addition of pre-dissolved sodium nitrite (29.5 g, 427 mmol, 4 eq.) solution in water (150 mL). The reaction mixture was stirred at room temperature for 16 hours. After complete consumption of the ingredients, 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 Na2SO4 and concentrated under reduced pressure to give a brown oily crude (20 g). The crude was purified by column chromatography on silica gel (100-200 mesh) using a hexane solution of 4% ethyl acetate as eluent to afford 2-chloro-5-iodo-6-methylpyridine as a brown oil (8 g, 30% yield). The product was confirmed by 1H NMR (400 MHz, CDCl3): δ 2.69 (s, 3H), 6.88 (d, J = 8.04 Hz, 1H), 7.95 (d, J = 8.24 Hz, 1H).LC-MS (m/z): 254.0 (M + H).
References
[1] Tetrahedron Letters, 2003, vol. 44, # 14, p. 2971 - 2973
[2] Patent: WO2014/39484, 2014, A1. Location in patent: Page/Page column 50; 51
