1H-[1, 2, 4, 5] oxatriazino [4, 5-b] phthalazine-6, ll-diones. The latter compounds are hydrolyzed in aqueous methanol to 4-hydroxy-l (2H)-phthalazinone, ketones, and nitrones. It1 was1 also shown that 2-isopropenyl-4-hydroxy-1 (2H)-phthalazinone reacted with nitrones in benzene to also form 1H-[1, 2, 4, 5] oxatriazino [4, 5-b] phthalazine-6, ll-diones in low yields.