Regioselectivity of [2+3] Cycloaddition of Triphenylnitrone to Nitroethene - AM1/COSMO Computational Study

Abstract

Two isomeric pathways for the [2+3] cycloaddition of triphenylnitrone to nitroethene in a dielectric medium corresponding to the relative permittivity of toluene was evaluated in therms of AM1/COSMO calculations. It was found that reaction leading to 4-nitro-2,3,3-triphenylisoxazolidine (path A) occurs via a zwitterionic intermediate, whereas the reaction leading to 5-nitro-2,3,3-triphenylisoxazolidine (path B) takes place in concerted way. The activation parameters estimated for both reaction pathways indicate that A is favored (∆GTSA = 34.33 kcal/mol; ∆GTSB = 43.37 kcal/mol). The reaction regioselectivity is in good agreement with the experimental data.