Density Functional Theory Study on the Mechanism of Organophos-phine-Catalyzed [4+2] Cycloaddition Reaction

Organophosphine-catalyzed cycloaddition reaction provides an efficient method for the construction of valuable heterocycles. In this article, density functional theory calculations were performed on the mechanism of a phosphine-catalyzed [4 +2] cycloaddition between conjugated dienes and enones reported recently. The overall reaction consisted of four sequential processes, namely the formation of the zwitterionic intennediate, intermolecular nucleophilic addition, intramolecular cyclization, and removal of the organophosphine. The activation free-energy barrier was estimated to be 84.4 kJ/mol, and the overall free-energy change was computed to be -18.8 kJ/mol. For the asymmetric variant of the reaction, the predicted enantioselectivity results were consistent with experimental findings, and what's more, a distortional strain model was proposed to understand the observed enantioselectivity. Lastly, the substituent effects concerning the diene substrate were explored, which revealed that an ester group on the C(2) position would exert a much stronger influent on the reactivity than that on the C(1) position. The conclusions drawn in this work can help organic chemists to optimize experimental conditions and design new reactions.

Automated summary

In this article, density functional theory calculations were performed on the mechanism of a phosphine-catalyzed cycloaddition reaction. The predicted enantioselectivity results were consistent with experimental findings, and the substituent effects concerning the diene substrate were explored.