2,5-Dichloronicotinaldehyde was prepared as follows: to a solution of 4-chloro-but-3-enonitrile (2.25 g, 22.3 mmol) in dimethylformamide (8.6 mL) was added phosphoryl chloride (10.4 mL, 111 mmol). The resulting reaction mixture was heated to 100 C overnight, cooled to 0 C and quenched with water. The product was extracted with dichloromethane and the organic layer was dried over magnesium sulfate, filtered and concentrated in vacuum. Recrystallization from hexane gave 2,5-dichloronicotinaldehyde.
