1.46 g of 1,4-dioxopyrazinamide (2) was homogeneously mixed with 5 mL of chlorobenzene and 12.1 g of trichlorophosphorus. The mixture was heated to 50 °C and the reaction was stirred for 50 minutes, followed by warming to 70 °C for 1 hour. Upon completion of the reaction, the mixture was cooled to room temperature, 1.52 g of pyridine was added, and the reaction was continued to 110 °C and maintained for 8 hours. The completion of the reaction was confirmed by TLC monitoring. The reaction mixture was evaporated to dryness under reduced pressure, washed with 5 mL of ice water and subsequently extracted with ethyl acetate (10 mL x 3). The organic phase was combined and washed twice with saturated brine. The organic phase was dried over anhydrous sodium sulfate and filtered, and the filtrate was evaporated to dryness under reduced pressure. Purification by chromatography, separation and vacuum drying gave 1.45 g of light yellow solid 3,6-dichloro-2-cyanopyrazine (3) in 52.55% yield.
