General procedure for the synthesis of 2,3,5,6,7,8-hexahydrophthalazine-1,4-dione from 3,4,5,6-tetrahydrophthalic anhydride: 3,4,5,6-tetrahydrophthalic anhydride (25 g, 0.164 mol) was dissolved in a 40% aqueous acetic acid solution (500 ml) containing sodium acetate trihydrate (26.8 g, 0.197 mol), followed by hydrazine hydrate ( 9.58 ml, 0.197 mol). The reaction mixture was heated to reflux overnight and then cooled to room temperature. The resulting solid product was collected by filtration, washed sequentially with water and ether and finally dried under vacuum to afford the target compound 2,3,5,6,7,8-hexahydrophthalazine-1,4-dione (23 g, 84% yield). The product was characterized by 1H NMR (250 MHz, d6-DMSO): δ 1.64 (4H, br s, 2×CH2), 2.34 (4H, br s, 2×CH2), 11.30 (2H, br s, 2×NH); the mass spectrum (ES+) showed m/e 167 [MH]+.
