Pyridazines Knoevenagel reaction

Knoevenagel reactions of azaenaminones 608 with Meldrum s acid give the azadienaminones 609, which undergo either base-catalyzed cyclization to the 3-oxopyridazin-4-carboxyxlic acids 610 or flash vacuum pyrolysis to the pyridazin-3-ones 611, Scheme 166 [82JCS(P1)1845],... 

The reactivity of pyridazine-3- and 4-carbaldehydes towards active methylene reagents under the conditions of Knoevenagel, Wittig, and Hantzsch-type reactions has been examined. The 4-aldehyde reacts readily with malononitrile and methyl cyanoacetate, and less readily with triethyl phos-phonoacetate, indane-l,3-dione and alkyl acetoacetates/ammonia (e.g.. Scheme 52). Condensation with nitroethane is successful, but nitromethane gives an unstable intermediate which decomposes. The 3-aldehyde has similar reactivity to the 4-aldehyde, but some reactions are unsuccessful due to reduced reactivity, or instability of the products <90JHC1313>. 

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