Tetrasubstituted pyridazines

A procedure based on benzylidene azines also appeared. Reactions of dibenzoylacetylene with 296 yielded tetrasubstituted pyridazines 297 via cycloaddition and subsequent spontaneous oxidation of the tetrahydropyridazines (Equation 74) <2005CJC57>. 

Cycloaddition of dimethyl l,2,4,5-tetrazine-3,6-dicarboxylate with EWG-substituted primary ketene N,0-acetals provides a tetrasubstituted pyridazine, methyl 4-amino-5,7-dioxo-6,7-dihydro-5/7-pyrrolo[3,4-4pyridazine-3-carboxylate <200681513>. 

Many alkyl- or aryl-substituted pyridazines (14) have been prepared by a direct one-step cyclization from an unsaturated 1,4-diketone (diacylethylene) and hydrazine. In the main symmetrically substituted diketones were employed, carrying aliphatic " or aromatic groups. Ethylene-substituted unsaturated 1,4-diketones afford tri- or tetrasubstituted pyridazines (14, R = =Rg = Rg = alkyl or aryl).2 -23 ... 

In this work the possibility of the existence of 1,2-dihydro isomer with the core structure 42 was not considered. Recently, however, it was shown that 1,2-dihydropyridazines could be prepared by careful electroreduction of the corresponding pyridazines, and that their stability depends significantly on the ring substitutions. Thus, dimethyl l,2-dihydropyridazine-3,6-dicarboxylate 43a (R = H) is reasonably stable and rearranges into the 1,4-dihydro tautomer 43b only at a more negative potential, while the tautomerization in its tetrasubstituted analog 43a (R = COOMe) occurs more readily (Scheme 14) [00TL647]. 

Supurgibekov MB, Yanyuk NS, Nikolaev VA (2011) Diaza-wittig reactions of diketoesters phosphazines synthesis of tetrasubstituted fluoroalkyl-containing pyridazines Russ. J Org Chem 47 1252-1255... 

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