Geometrical distortions and charge transfer in munchnöne regio-selectivity: A conceptual density functional study

International Journal of Quantum Chemistry

4 years ago

Geometrical distortions and charge transfer in munchnöne regio-selectivity: A conceptual density functional study

Ramón Alain Miranda-Quintana, Marco Martínez González, Luis A. Montero-Cabrera, David Hernández-Castillo

Dipolar cycloaddition reactions involving munchnönes and simple dipolarophiles provide a versatile synthetic route toward pyrrole derivatives. However, despite their widespread use, there are still debates regarding the factors governing the regio-selectivity of these reactions. In this contribution, we study the regio-selectivity of 1,3-dipolar cycloadditions of munchnönes and alkenes, and the ability of conceptual density functional theory (c-DFT) descriptors to correctly study these processes. We base our analysis on the variation of different reactivity descriptors along the reaction path, calculated for the whole reacting complex, and for the isolated species, with the strained geometries they present within this supra-molecular aggregate. The study of several global descriptors indicates that the path leading to the preferred product proceeds via an asynchronous mechanism, with the maximum extent of charge transfer occurring after the transition state. This helps to understand why several reactivity principles fail to correctly account for the position of the transition state in this case. This also explains why local c-DFT descriptors fail to predict the observed majoritarian regio-isomer. These results highlight the fundamental role of the distortion effects for determining the extent of charge transfer between the reactants, and thus their impact on the reactivity and regio-selectivity in these reactions. Dipolar cycloadditions involving munchnönes are a powerful tool in the synthesis of many heterocyclic compounds. Therefore, there is recent increasing interest in the elucidation of the factors governing their regio-selectivity. First-principles calculations show that the geometrical distortion of the reactants, and the charge transfer between them, must be taken into account to accurately predict the formation of the preferred regio-isomer.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/qua.25444