SYNTHESIS AND STRUCTURE OF PARA-SUBSTITUTED ARYLHYDRAZONES OF ETHYL 2,4-DIOXOPENTANOATE

Acyl- and thioacylhydrazones of 1,3-diketones constitute a class of compounds of considerable interest in terms of their tautomeric possibilities and continue to attract increasing attention. Interest in the detailed structure of acylhydrazones stems primarily from their ability to exist in different tautomeric forms. Depending on the structural features of the dicarbonyl component, a three-way ring–chain equilibrium may be expected among the linear (hydrazone and enehydrazine) and cyclic 5-hydroxy-2-pyrazoline tautomeric forms of acylhydrazones of 1,3-diketones. It should be noted that a two-form prototropic equilibrium has been observed for acylhydrazones of both 1,3-ketoesters and 1,3-ketoaldehyde derivatives.