[3+2] Cycloaddition Reaction of C-Phenyl-N-methyl Nitrone to Acyclic-Olefin-Bearing Electron-Donating Substituent: A Molecular Electron Density Theory Study

The [3 + 2] cycloaddition (32CA) reactions of C-phenyl-N-methyl nitrone to acyclic olefins bearing electron donating and weak electron withdrawing groups lead to complete ortho regiose-lectivity. The experimentally observed ortho selectivity can be rationalized from the activation energies of the located transition states at DFT/MPW1PW91/6-311G(d,p) level of theory. The reaction of this nitrone to ethyl vinyl ether is predicted to be non-polar by global electron density transfer (GEDT) calculations. Bonding evolution theory (BET) study led to topological characterization of the reaction pathway into different phases and indicated initial rupture of the olefinic double bond followed by the formation of pseudoradical centres and earlier formation of C-C bond. Quantum theory of atoms in molecules (QTAIM) study of electron density was performed for (3,-1) critical points at the region near the forming C-C and C-O bonds and was found to be in complete agreement with the Electron localization function (ELF) topological analysis. Electrostatic potential surface study for the transition states indicated greater mutual penetration distances of C-C forming bond compared to the C-O forming bond.