General procedure for the synthesis of 5,6-dichloronicotinonitrile from 5,6-dichloronicotinamide: 5,6-dichloronicotinamide (8.4 g, 44 mmol) was suspended in 76 mL of thionyl chloride. The reaction mixture was stirred under reflux conditions for 72 hours. Upon completion of the reaction, the solvent was removed by vacuum concentration and the residue was dissolved in chloroform. The organic layer was washed with water and dried with anhydrous sodium sulfate. After removal of the solvent by concentration under reduced pressure, the crude product was first purified by reversed-phase column chromatography (eluent: acetonitrile/dichloromethane), followed by crystallization in ethyl acetate to afford the target product, 5,6-dichloronicotinonitrile, in 78% (5.95 g) yield. The structure of the product was confirmed by 1H-NMR (CDCl3): δ = 8.05 (s, 1H), 8.60 (s, 1H).
