New synthetic approaches to condensed pyridazinones: Alkylpyridazinyl carbonitriles as building blocks for the synthesis of condensed pyridazinones

Article abstract of DOI:10.1016/0040-4020(95)00829-W

The pyridazinyl-5-carbonitriles (3a-d) were prepared via condensing the aryl hydrazones 2a-d with ethyl cyanoacetate. Similar condensation of 2a with malononitrile gives the pyrido[2,3-c]pyridazine derivative (8). Compounds 3a-d reacted with elemental sulphur in refluxing ethanolic solutions in the presence of triethylamine to yield the thieno[3,4-d]pyridazinones 9a-d. The 1,3,4-thiadiazaacenaphthene 12 was prepared via reacting 9e with diethyl fumarate. In contrast, only the phthalazines 14a-c were produced from the reaction of 13a-c with 9e. Compounds 9a-c reacted with acrylonitrile to yield the 1,3,4-thiadiazaacenaphthenes 18a, b. Compound 3a condensed with benzaldehyde to yield 19a. Condensation of 3a, c, d with dimethylformamide dimethylacetal afforded 19b-d. Compound 19b cyclized into 20b when refluxed in acetic acid in the presence of ammonium acetate. This same product was obtained from the reaction of the amide 3g with formaldehyde in refluxing pyridine. The reaction of 3a, c with arylidenemalononitrile (23a, b) gives the tetrahydrophthalazines 25a-c. The pyridazin-4-ones 26a-d were prepared from the reaction of 2a-d with dimethylformamide dimethylacetal in refluxing dioxane. The crystal and molecular structure of compound 18a was solved by X-ray analysis.