1-substituted 3-dimethylaminoprop-2-en-1-ones as building blocks in heterocyclic synthesis: new routes to 6-aroylpyridazin-3-ones, 4,6-diaroylpyridazin-3-imines and 3-aroylpyrazolo[5,1-c][1,2,4]triazines

The Wittig reaction of 3-aryl/heteroaryl-2-arylhydrazono-3-oxopropanals 2c, d with ethyl triphenylphosphonioacetate in the presence of methanesulfinylm ethyl carbanion affords 2-substituted 6-aroylpyridazin-3(2H)-ones (5a,b) in moderate yields. Compounds 5a,b were also obtained from the reaction of 2c ,d with acetic anhydride in presence of potassium acetate. 1-Substituted-3- dimethylaminoprop-2-ene-1-ones 1b,d couple with 5-methylisoxazole-3-diazoni um chloride to yield isoxazolylhydrazonopropanals 2g,h. Compounds 1a,b coup le with 5-methylpyrazole-3-diazonium chloride to yield pyrazolylhydrazonopr opanals that readily cyclise to the corresponding pyrazolo[5,1-c][1,2,4]tri azines. The reactivity of 2-arylhydrazono-3-oxopropanals 2a-f towards a var iety of active methylene reagents was investigated.