Abstract
AbstractA reaction involving 1‐hydrazinophthalazine (hydralazine, 1)designed to give a condensed heterocyclic system in which an eight membered ring is fused to phthalazine was investigated. With phthalaldehydic acid (2) the expected system was obtained. However, it occurs as an easily convertible mixture of ring‐chain tautomers. It was found that the course of the reaction depends on the solvent. Thus, 6,7‐dihydro‐7‐hydroxy‐12H‐phthalazino[2,1‐b][2,4]benzodiazocin‐12‐one (5) and 2‐(2‐formylbenzoyl)‐1‐hydrazono‐1,2‐dihydrophthalazine (6) were the products of the reaction of 1 with 2 in aqueous medium. Upon prolonged standing this mixture converts into 3‐(2‐carboxyphenyl)‐s‐triazolo[3,4‐a]phthalazine (8). In contrast, the isomeric ring‐chain tautomers 2‐(1‐aminophthalazino)‐3‐hydroxy‐1‐oxoisoindole (12) and 1‐[2‐(2‐formylbenzoyl)hydrazino]phthalazine (13) were formed when the reaction was run in ethanol as solvent.
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