A mixture of (2H)-pyrazinone (4.2 g, 0.044 mmol) and phosphorous oxybromide (25 g, 0.088 mole) was heated at 105 °C for 1.5 h. After cooling to room temperature, the mixture was poured on crushed ice (300 g) and made neutral with sodium hydrogen carbonate. The mixture was extracted with dichloromethane (2 x 100 mL). The extract was dried with magnesium sulfate and evaporated under vacuum. The residue was distilled under vacuum (70 °C, 12 torr). 2-Bromopyrazine (3.2 g, 46 %) was obtained as a colourless liquid[1].
[1] Laurence Decrane, Alain Turck, Nelly Plé. “Metalation of bromodiazines. Diazines XL.” Journal of Heterocyclic Chemistry 42 4 (2009): 509–513.
