Synthesis
The general procedure for the synthesis of 4-bromo-3,6-pyridazinedione from bromomaleic anhydride was as follows: hydrazine sulfate (2.25 g, 17.2 mmol) was dissolved in boiling water (20 mL) under stirring conditions. Bromomaleic anhydride (2.6 mL, 28.2 mmol) was added dropwise to this solution through an addition funnel. The reaction mixture was heated under reflux conditions (100 °C) for 19 h and subsequently cooled to room temperature. The reaction mixture was filtered through a medium glass material sintered glass funnel and a white precipitate was collected. The precipitate was washed with acetone (3 x 5 mL) and then dried under vacuum to afford the target product 4-bromo-1,2-dihydropyridazine-3,6-dione (2.85 g) as a white powder in 87% yield (based on gravimetric analysis) with a melting point of 262°C.
References
[1] Journal of Organic Chemistry, 2014, vol. 79, # 21, p. 10311 - 10322
[2] Patent: WO2014/145485, 2014, A2. Location in patent: Paragraph 00207; 00290
[3] Tetrahedron Letters, 2017, vol. 58, # 14, p. 1373 - 1375
[4] Patent: US6579875, 2003, B1
[5] Patent: US6303605, 2001, B1
