One-step ring condensation of hydrazine derivatives and cyclic anhydrides

•Ring-condensation.•Pyridazinone.•Over-accommodation effects.•Molecular and crystal structure.

Hydroxypyridazinone and pyrroledione rings condensation in the reactions of hydrazine hydrate with citraconic, 2,3-dimethylmaleic, succinic and cis-cyclohexanedicarboxylic anhydrides have been conducted in the HCl aqueous solution. The pyridazine-ring condensation yields products unexpected for these conditions. They have been identified by 1H/13C NMR and X-ray diffraction. The course of the reaction toward the five- and six-membered ring condensation strongly depends on methyl and other substituents in the anhydrides and in hydrazine. The obtained products indicate that the ring condensation is controlled by the molecular strains and steric hindrances between the substituents in anhydrides and pyridazinone products. The condensation of cyclic anhydrides with hydrazines has been reduced to one-step reaction and its yield significantly increased.

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