Reactions of N-alkylhydrazones of aliphatic ketones

Abstract

For the first time data concerning the reactions of N-alkylhydrazones of aliphatic ketones have been systematized. The possible reaction centres of hydrazones and the main lines of attack for electrophilic and nucleophilic reagents have been distinguished. Differences in the reactivity of N-alkyl and N-arylhydrazones have been studied. The types of tautomerism of hydrazones and their impact on the reactivity of these compounds have been considered. Most reactions occurring on the sp2-hybridized carbon atom lead to formation of azocompounds, which are generally aliphatic radical sources or initiators of radical processes. The interaction of hydrazones with oxidising reagents leading to the corresponding bisazocompounds has been studied. For a number of N-acylation hydrazones the ring-chain tautomerism has been described, as a result these compounds exist in cyclic and acyclic forms. The general methods for construction of heterocyclic compounds based on N-alkylhydrazones of aliphatic ketones due to cyclization of hydrazones with bis-functional reagents on both nitrogen atoms, as well as the nitrogen atom and the carbon atom have been considered. Hydrazone-enhyidrazine tautomerism is inherent to hydrazones of aliphatic ketones with the α-methylene group; it causes a simultaneous attack of dielectrophiles on the sp3-hybridized carbon atom and the nitrogen atom of hydrazone and can be used to construct derivatives of pyridazine and pyrazole, and the use of compounds of phosphorus and of silicon as dielectrophiles results in formation of phosphodiazoles and silapyrazolines, respectively. Reduction reactions for C=N bond of N-alkylhydrazones of aliphatic ketones have been studied.