Substituted Hydrazonals as Building Blocks in Heterocyclic Synthesis: A New Route to Arylhydrazonocinnolines

Abstract

2-heteroylhydrazonopropanals 2a–e and 3-oxo-2-arylhydrazonopropanals 2f–k were prepared via coupling of enaminones 1 with aromatic diazonium salts. Compounds 2a–c condensed with hydrazine hydrate to yield the corresponding hydrazones 3a–c which afford on cyclisation the cinnoline derivatives 6a–c, while condensation of 2g, j with hydrazine hydrate directly yielded the pyrazole derivatives 4g–j. Condensation of 2a–c, f, g with phenyl hydrazine gave the corresponding phenyl hydrazone derivatives 7a–c, f, g. Structures of 2a, h and 3a were assessed by single crystal X-ray analyses.