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 beta-tri- or beta-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-butadiene with methyl 2-acetylacetoacetate produce 1-alkoxycarbonyl-4,5(4H,5H)-(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(4H, 5H)-(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(4H,5H)-(methoxycarbonylcyclopropyl)-1H-pyrazole was determined.