General procedure for the synthesis of 5-amino phthalazine using 5-nitro phthalazine as starting material: 0.88 g (5.0 mmol) of 5-nitro phthalazine was dissolved in 30 mL of tetrahydrofuran at 50 °C, followed by the addition of 4.37 g (25.1 mmol) of sodium bisulfite dissolved in a solution of 15 mL of water. The reaction mixture was stirred continuously at 50 °C for 15 min. Upon completion of the reaction, the organic phase was extracted with ethyl acetate (3 x 100 mL) and the combined organic phases were washed with brine (50 mL) and dried with anhydrous magnesium sulfate. After filtration, the solvent was removed by concentration under reduced pressure to give the crude product as a bright yellow precipitate. The crude product was recrystallized in hot methanol to give 0.49 g (67% yield) of purified 5-aminophthalazine. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6) and 13C NMR (100.17 MHz, DMSO-d6) as follows: 1H NMR δ: 9.80 (s, 1H), 9.60 (s, 1H), 7.60 (dd, J = 4.6, 7.6 Hz, 1H), 7.20 (dd, J = 1.9, 4.6 Hz, 1H), 7.02 (d, J = 7.6 Hz, 1H), 6.50 (s, 2H); 13C NMR δ: 150.1,146.5,145.1,133.2,126.1,114.7,114.1,112.2.
