The Chemistry of Heterocyclic Hydrazonoyl Halides

Abstract

Hydrazonoyl halides have emerged as an important class of intermediates, particularly for the synthesis of heterocyclic compounds. This chapter discusses the synthesis, properties, and reactions of Hydrazonoyl Halides. The mechanisms of some of the reactions and the structures of some of the products are outlined. Direct halogenation of arylhydrazone derivatives of both aliphatic and aromatic aldehydes with the appropriate halogen in glacial acetic acid is an excellent method for the synthesis of the corresponding hydrazonoyl halides. Halides are also obtained by refluxing with N- bromosuccinimide in dry carbon tetrachloride. Furthermore, bromination of aldehyde N-heteroarylhydrazones in acetic acid in the presence of sodium acetate sometimes leads to intramolecular cyclization of the initial hydrazonoyl bromides to yield the corresponding cyclized products. However, from the foregoing survey of heterocyclic hydrazonoyl halides, it appears that the main emphasis has been restricted to both their preparation and use as intermediates for further synthesis. Large areas of their chemistry, particularly regarding their physical and biological properties, remain to be developed.