Understanding the different reactivity of ()- and ()-β-nitrostyrenes in [3+2] cycloaddition reactions. An MEDT study.

The experimental reactivity of isomeric ()- and ()-β-nitrostyrenes participating in [3+2] cycloaddition (32CA) reactions has been analysed on the basis of molecular electron density theory (MEDT) at the HF/6-311G(d,p), B3LYP/6-311G(d,p) and B97X-D/6-311G(d,p) computational levels. It was found that the polar 32CA reactions with 5,5-dimethylpyrroline--oxide proceed a one-step mechanism, characterised by the attack of the nucleophilic oxygen centre of the nitrone on the electrophilically activated β-position of these nitrostyrenes. This behaviour is completely understood by means of the analysis of the conceptual DFT reactivity indices.