DFT study on the intramolecular nitrone–alkene cycloaddition reaction of the N-3-alkenylnitrone

Intramolecular nitrone–alkene cycloaddition (INAC) of the N-alkenylnitrone represents an appealing method for the syntheses of bicyclic and polycyclic isoxazolidines. In this paper, we have conducted the systematic theoretical study on the regioselectivity in the INAC reactions of various N-3-alkenylnitrones which carry synthetically relevant substituents by using DFT method. Substitution at the C2- or C6-position exhibits the Z-selectivity almost exclusively, while substitution at the C1-position enhances the E-selectivity. Marcus theory analyses show the involvement of both the thermodynamic and intrinsic contributions in determining the Z-selectivity. In addition, the introduction of the substituents on the olefinic bond can reduce the rate of the INAC reaction. However, an additional method, namely the incorporation of an aromatic ring into the N-3-alkenylnitrone backbone at the C3- and C4-positions, has been provided. This method can not only enhance the Z-selectivity but also increase the rate of the INAC reaction.