Heteroaromatic hydrazides

By reaction with hydrazides. In these reactions, aliphatic, aromatic and heteroaromatic hydrazides 118 condense and cyclize with ethyl (or methyl) 3-oxobutanoate 1 to give pyrazol-3-ones 3 or 4 in one... 

Hydrazides of vicinal acetylene-substituted derivatives of benzoic and azole carboxylic acids are important intermediate compounds because they can be used for cyclization via both a- and /3-carbon atoms of a multiple bond involving both amine and amide nitrogen atoms (Scheme 131). Besides, the hydrazides of aromatic and heteroaromatic acids are convenient substrates for testing the proposed easy formation of a five-membered ring condensed with a benzene nucleus and the six-membered one condensed with five-membered azoles. 

The cyclization of hydrazides of aromatic and heteroaromatic acids is likely to give four most probable products diazepines, diazines, 5-iV-aminolactams, and y -iV-aminolactams. 

Direct amination of 3(2//)-pyridazinones occurs when they are heated with hydrazine hydrate and this is a convenient route to many 4-amino-6-substituted-3(2//)-pyridazinones (Scheme 11). The reaction generally gives high yields and amination is regiospecific when the 6-position is occupied by an aromatic or heteroaromatic ring, but the parent 3(2/ -pyridazinone gives a mixture of the 4- and 5-amino-3(2//)-pyridazinones. The reaction tolerates jV-methyl substitution of the pyridazinone, but is sensitive to steric factors the presence of a 5-substituent causes a marked reduction in reaction rate, and amination does not occur with 4-phenyl-3(2//)-pyridazinone. With maleic hydrazide 4-hydrazination occurs, possibly by displacement of an intermediate amino compound or by oxidation of an intermediate 4,5-dihydro-4-hydrazino adduct both 4-hydrazino- and... 

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