A MOLECULAR ELECTRON DENSITY THEORY STUDY OF MECHANISM AND SELECTIVITY OF THE INTRAMOLECULAR [3+2] CYCLOADDITION REACTION OF A NITRONE–VINYLPHOSPHONATE ADDUCT

Abstract

The selectivity and the molecular mechanism of the intramolecular [3+2] cycloaddition reaction of a nitrone–vinylphosphonate adduct was
computationally studied within the molecular electron density theory using density functional theory method at the B3LYP/6-31G(d,p)
level of theory. Conceptual density functional theory indices show that the nitrone–vinylphosphonate adduct has dual strong electrophilic
and nucleophilic character. Local Parr functions reactivity indices reveal that this reaction favors the formation of the fused regioisomers
in accordance with the experimental data. Analysis of different energetic profiles indicates that the fused-endo competitive pathway is
favored kinetically, whereby this intramolecular reaction is characterized by exothermic and exergonic character. The geometry of
transition states structures shows that the mechanism of this cycloaddition reaction is synchronous. Electron localization function
topological analysis of the changes in electron density during the most favored reaction pathway shows that the mechanism is
synchronous non-concerted.