Abstract
The cycloaddition of the ethoxycarbonylformonitrile N-arylimides 2 to benzylideneacetone afforded two regioisomers, 5-acetyl- and 4-acetyl-dihydropyrazoles, but the cycloaddition of 2 to benzoylacetone afforded 4-acetyl- and 4-benzoyl-pyrazole; some pyrazolopyridazin-7-one and pyrazolopyridazine derivatives were also synthesized.