Convertible bonds dilution effect

The steric effect has an important influence on pyridazine formation. This is particularly the case when the double bond of the anhydride is incorporated in a cyclic system, or with cyclic 1,2 diesters. At least four types of products can be produced and they were identified as a monohydrazide as 24, a dihydrazide as 27, an iV-aminomaleimide derivative as 25, or a pyridazinone as 21. The dihydrazides are relatively easily converted into pyridazinones when heated with excess hydrazine or in dilute hydrochloric acid, and treatment with nitrous acid has the same effect. - ... 

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