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 methanesulfinylmethyl 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-diazonium chloride to yield isoxazolylhydrazonopropanals 2g,h. Compounds 1a,b couple with 5-methylpyrazole-3-diazonium chloride to yield pyrazolylhydrazonopropanals that readily cyclise to the corresponding pyrazolo[5,1-c][1,2,4]triazines. The reactivity of 2-arylhydrazono-3-oxopropanals 2a–f towards a variety of active methylene reagents was investigated.