[Cl:1][C:2]1[CH:3]=[N:4][NH:5][C:6](=[O:9])[C:7]=1[Cl:8].[Br:10]Br>O>[Br:10][C:3]1[C:2]([Cl:1])=[C:7]([Cl:8])[C:6](=[O:9])[NH:5][N:4]=14,5-dichloro-1H-pyridazin-6-one (1.95 g, 11.8 mmol) and bromine (0.73 ml, 14.2 mmol) are suspended in water (10 ml) and the mixture heated under microwave irradiation to 180° C. for 30 min. The resulting reaction mixture is filtered and the crude solid obtained washed thoroughly with water, then DCM, to yield 3-bromo-4,5-dichloro-1H-pyridazin-6-one, 2.06 g, as a white solid (71.5% yield).
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