General procedure for the synthesis of 4-chloro-5-nitro-2-trifluoromethylpyridine from 5-nitro-2-(trifluoromethyl)pyridin-4-ol: to a stirred mixed solution of 5-nitro-2-(trifluoromethyl)pyridin-4-ol (3.9 g, 0.01 mol), PCl5 (4.5 g, 0.02 mol) and POCl3 (2 mL, 0.02 mol) The reaction was heated to 80°C for 16 hours. The reaction progress was monitored by TLC to confirm the completion of the reaction. The reaction mixture was cooled to room temperature, diluted with dichloromethane (DCM) and washed sequentially with water (100 mL), saturated NaHCO3 solution (100 mL) and brine (100 mL). The organic phase was dried with anhydrous Na2SO4, filtered and concentrated under reduced pressure to give 4-chloro-5-nitro-2-(trifluoromethyl)pyridine as a yellow oil. Yield: 3 g (94%); 1H NMR (400 MHz, DMSO-d6): δ 9.42 (s, 1H), 8.56 (s, 1H); MS (ESI+) m/z 227.34 [M+H]+.
