A molecular electron density theory study of the [3 + 2] cycloaddition reaction of nitronic ester with methyl acrylate

The [3 + 2] cycloaddition (32CA) reaction of nitronic ester with methyl acrylate has been studied within the molecular electron density theory to analyse the mechanism and experimentally observed regioselectivity. Electron localisation function (ELF) study predicts zwitter-ionic character of the nitrone, allowing its participation in zw-type 32CA reactions associated with high energy barrier demanding overcome through appropriate electrophilic–nucleophilic interactions. Analysis of the CDFT indices predict the global electronic flux from the strong nucleophilic nitrone to the electrophilic methyl acrylate. These 32CA reactions are exergonic with negative reactions Gibbs free energies along ortho regiochemical pathway. Among the ortho and meta regiochemical pathways, ortho path is preferred owing to the higher thermodynamic stability of the cycloadducts. Bonding evolution theory (BET) study predicts one-step mechanism with early transition states for the ortho and meta pathways, in conformity with the ELF topological study at the transition states.