Acetylacetaldehyde Dimethyl Acetal as Versatile Precursors for the Synthesis of Arylazonicotinic Acid Derivatives: Green Multicomponent Syntheses of Bioactive Poly-Heteroaromatic Compounds

A simple and efficient one-pot synthesis of interesting arylhydrazonals could be achieved via coupling of acetylacetaldehyde dimethyl acetal with aromatic diazonium salts. Dimroth type rearrangement was observed during the reaction of the arylhydrazonals with malononitrile or ethyl cyanoacetate leading to the formation of arylazonicotinic acid derivatives. The reaction of arylhydrazonals with malononitrile and aldehydes in the presence of DABCO afforded 4-styryl-1,2-dihydropyridine-3-carbonitrile whose structure was established by X-ray crystallography. Pyrazolyl-enaminone was accomplished and used as a scaffold to synthesize bioactive fused heterocyclic compounds such as 1,2,4-triazolo[1,5-a]pyrimidine 28, benzo[4,5]imidazo[1,2-a]pyrimidine 30 and pyrazole[1,5-a]pyrimidine derivatives 32.