General procedure for the synthesis of 4,6-dichloronicotinonitrile from 4,6-dichloropyridine-3-amide: Pyridine (20.3 mL, 250 mmol) was slowly added to an acetonitrile (180 mL) suspension of 4,6-dichloronicotinamide (8.00 g, 41.9 mmol) at room temperature. Subsequently, phosphorous trichloride (11.7 mL, 126 mmol) was added dropwise over 3 minutes. The reaction mixture was heated to 60 °C with continuous stirring for 1.5 hours. Upon completion of the reaction, the solution was cooled to room temperature and carefully poured into 0.8 M aqueous sodium hydroxide solution (600 mL). Multiple extractions were performed with ethyl acetate (6 x 400 mL) and the organic phases were combined. The organic phase was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The residue was purified by silica gel fast column chromatography (30% ethyl acetate/hexane as eluent) to afford 4,6-dichloronicotinonitrile as a light orange solid (6.41 g, 88% yield).1H NMR (400 MHz, CDCl3) δ 8.67 (s, 1H), 7.58 (s, 1H).
