Introduction
Acid hydrazides are organic derivatives of hydrazine. Transformations using these species to synthesize heterocycles have been research objectives for over a century.[1] Because of their wide utility, acid hydrazides have always been attractive precursors for the synthesis of heterocycles. They have been used for the synthesis of five- and six-membered heterocycles incorporating two or more heteroatoms in the ring, such as indoles, pyrazoles, oxadiazoles, and triazoles which display a wide spectrum of biological activities.[2] Hydrazide analogues[3] also possess useful biological activities.[4] Isonicotinic acid hydrazide has been used in medical practice.[5] In organic synthesis, acid hydrazides have similarities with Weinreb amides, as plenty of sites are available for forming a stable metal chelate. Thus, they are used as effective acyl donors for the synthesis of ketones[6] and amides.[7] Acid hydrazides can be easily prepared by the combination of hydrazine with various acyl derivatives, including esters, cyclic anhydrides, and acyl halides.
