5- Hydrazino-3 -pyridazinones, reaction

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... 

Reaction of monosubstituted hydrazines with the readily available spirocyclic cyclo-propanedicarboxylates (163) gives 1-substituted l,4,5,6-tetrahydropyridazin-3(2/i)-ones (164) in a one-pot reaction (Scheme 123). Initial attack is thought to be a homo-Michael type of addition by the substituted hydrazine nitrogen decarboxylation occurs under the reaction conditions. The formation of the alternative pyridazinone (165) by attack of the unsubstituted hydrazino nitrogen was only observed (<5%) with (4-chloro-2-methylphenyl)hydrazine <93H(36)219>. 

During the synthesis of oxadiazolyl pyridazinones, by treating 2- crr-butyl-4-chloro-5-(ethoxycarbonylmethoxy) -3(2H)-pyridazinone (Ci) with hydrazine hydrate in ethanol at reflux for 6-8 hours (Scheme 7), we obtain an unexpected product El in good yield, instead of the anticipated product of the corresponding acetylhydrazine. Alazawe had previously reported that methoxyl group at 6-position of the pyridazinone could be replaced by the hydrazino group. For this reason, we assume that the key step of this reaction is the formation of intermediate D. In fact, we also found that 2-(un)substituted-4, 5-... 

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