Reaction of Some 1,2-Diaza-1,3-butadienes with Activated Methine Compounds. A Straightforward Entry to 1,4-Dihydropyridazine, Pyridazine, and 4,5(4H,5H)-Cyclopropylpyrazole Derivatives

1-Aminocarbonyl-1,2-diaza-1,3-butadienes with β-tri- or β-dicarbonyl compounds containing at least two keto functions give 1,4-dihydropyridazines, while hydrazone 1,4-adducts are obtained in the case of compounds containing one or no keto function. 1,4-Dihydropyridazines are transformed into pyridazines. The same substrates with 3-phenoxypentane-2,4-dione afford pyridazines. Surprisingly, 1-alkoxycarbonyl-1,2-diaza-1,3-butadienes with methyl 2-acetylacetoacetate produce 1-alkoxycarbonyl-4,5(4 H,5 H )-(alkoxycarbonylcyclopropyl)pyrazoles deriving from 1-alkoxycarbonyl-1,2-dihydropyridazine intermediates by ring contraction. These pyrazole derivatives with acetic acid show ring expansion to 1-alkoxycarbonyl-1,4-dihydropyridazines that can be converted into 1,4-dihydropyridazines with sodium hydroxide. 1-Alkoxycarbonyl-4,5(4 H,5 H )-(alkoxycarbonylcyclopropyl)pyrazoles or 1-alkoxycarbonyl-1,4-dihydropyridazines with trifluoroacetic acid provide 1-aminopyrroles via 1-alkoxycarbonyl-1,4-dihydropyridazine intermediates in the case of pyrazoles. The X-ray crystal structure of 1- tert -butoxycarbonyl-3,5-dimethyl-4-methoxycarbonyl-4,5(4 H,5 H )-(methoxycarbonylcyclopropyl)-1 H -pyrazole was determined.