At -10 °C, sodium nitrite (4.18 g, 60.7 mmol) in water (6 mL) was added to a 48% HBr solution of 3-amino-6-chloropyridazine (3.0 g, 23.3 mmol). Bromine (11.2 g, 3 eq) was slowly added, and the reaction was stirred at room temperature for 48 hours. A solution of NaOH (16.8 g) in water (42 mL) was added, and the organic layer was extracted with Et2O, dried over Na2SO4, and evaporated. The title compound was given as a white solid in 44% yield after rapid chromatographic purification using DCM/cyclohexane 50/50 as eluent.
