Step 1: Synthesis of 2,6-dichloro-4-methyl-3-nitropyridine from 2,6-dichloro-4-methylpyridine
1.1 Suspend 2,6-dichloro-4-methylpyridine (1 g, 6.17 mmol) in trifluoroacetic anhydride (5 mL, 35.4 mmol) and cool to 0 °C.
1.2 Nitric acid (0.579 mL, 12.96 mmol) was slowly added dropwise to the above suspension at 0 °C.
1.3 After the dropwise addition was completed, the reaction mixture was stirred at room temperature for 18 hours.
1.4 The reaction mixture was slowly added to a pre-cooled aqueous solution (8 mL) of sodium metabisulfite (1.183 g, 6.17 mmol) and stirring was continued for 2 hours at room temperature.
1.5 The pH of the reaction mixture was adjusted to 7 using 8N NaOH solution.
1.6 The reaction mixture was extracted twice with dichloromethane (CH2Cl2).
1.7 The organic layers were combined, washed with brine, dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated under reduced pressure to afford the target product 2,6-dichloro-4-methyl-3-nitropyridine (1.187 g, 5.73 mmol, 93% yield) as a white solid.
1.8 Product identification: retention time (tR) 1.07 min (LC-MS 2); electrospray ionization mass spectrometry (ESI-MS): 208 [M + H]+ (LC-MS 2); 1H NMR (400 MHz, DMSO-d6) δ ppm 2.39 (s, 3H), 7.90 (s, 1H).
