The general procedure for the synthesis of 5-bromo-6-phenylpyridazin-3(2H)-one from 3,4-dibromo-5-phenylfuran-2(5H)-one was as follows: to a solution of 3,4-dibromo-5-phenylfuran-2(5H)-one (600 mg, 1.887 mmol) in ethanol (5 mL) at 0 °C, hydrazine hydrate (0.102 mL, 2.076 mmol). The reaction mixture was stirred at room temperature for 10 min, followed by heating to reflux and kept for 2 h. The reaction was carried out on a cooled surface with the addition of hydrazine hydrate (1.076 mmol). Upon completion of the reaction, the mixture was cooled to room temperature, at which time a precipitate was generated. The precipitate was collected by filtration and washed with cold ethanol to give the final 5-bromo-6-phenylpyridazin-3(2H)-one (458 mg, 99% yield) as a light orange solid.LCMS analysis showed m/z = 251 [M + H]+ .
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