Structure-reactivity correlation for the kinetics of the reaction of substituted 4-phenyl-1,4-dihydropyridines formation

Abstract

Quantitative structure-reactivity correlations for the kinetics of the Hantzsch's synthesis of substituted 4-phenyl-1,4-dihydropyridines in the reaction between ethyl m- and p-substituted benzylidene acetoacetate and enamine has been studied. The reaction kinetics was followed using spectrophotometric measurements. It was found that the reaction correspond to the second-order kinetics. Quantitative structure-reactivity correlations of log k with the corresponding substituent constants (s,s+,sI and sR+) using Hammett and extended Hammett equation (DSP equation). They show linear relationship with positive values of reaction constants (r). The obtained data were processed by the linear regression analysis. It is confirmed that Michael's addition of enamine to benzylidene represents the slow step of the reaction with high positive charge at the benzylidene molecule. MO calculations were performed and they were also in agreement with the conclusions derived from structure-reactivity correlations.