5-Bromo-3-hydroxyisobenzofuran-1(3H)-one (954 mg, 4.17 mmol) was used as starting material and suspended in isopropanol (10 mL). The suspension was heated to 90 °C and maintained for 1.5 hours. Subsequently, hydrazine monohydrate (0.4 mL, 8.25 mmol) was added in four portions. Upon completion of the reaction, the resulting suspension was filtered and the filter cake was washed with isopropanol to yield 6-bromophthalazin-1(2H)-one (813 mg, 87% yield) as a beige solid.The molecular weight was determined to be 227.12 (M + H)+ by LC-MS.
