Unveiling the mechanism, regiochemistry and substituent effects of the [3 + 2] cycloaddition reactions of C, N-diaryl nitrile imine to ethylene derivatives from the molecular electron density theory perspective

Abstract

The [3 + 2] cycloaddition (32CA) reactions of C-(4-methoxyphenyl)-N-phenyl nitrile imine (NI) with a series of ethylene derivatives of increased electrophilic character have been studied within the framework of Molecular Electron Density Theory (MEDT). These 32CA reactions are kinetically controlled with activation Gibbs free energies between 14.8 and 24.0 kcal mol−1, and with the preferred regioselectivity involving the nucleophilic attack of the carbenoid carbon of NI on the non-substituted carbon of the electrophilic ethylenes in agreement with the experimental outcomes. The presence of electron-withdrawing substituents in the ethylene makes the 32CA reaction of forward electron density flux (FEDF) more quickly, relative to that with nucleophilic propene, showing the highest activation parameters and non-polar character. Electron localization function (ELF) and atom-in-molecules (AIM) topological analysis of the electron density at the transition state structures characterize the non-concerted nature of these one-step cb-type 32CA reactions.