Computational DFT study of the 1,3-dipolar cycloadditions of 1-phenylethyl-trans-2-methyl nitrone to styrene and 1-phenylethyl nitrone to allyl alcohol

Theoretical calculations were performed at the modest B3LYP/6-31G(d) level of DFT to interpret the regioselectivity and enantioselectivity and also to predict diastereofacial selecitivity for 1,3-dipolar cycloaddition reaction of two known nitrones leading to a diastereomeric excess of the products. In this respect, N-substituted and C-substituted nitrones were considered for reactions with the substituted dipolarophiles like styrene and allyl alcohol. The reactions were studied by calculating the potential energy surface of the addition process and rationalizing in terms of the reactivity index of global electrophilicity. For the reactions considered, trends in reactivity, i.e., the regio- and exo/endo-selectivity and product ratios have been explained in terms of frontier orbitals interaction, electrophilicity difference, the rate constant values and an analysis of Pauling's bond order and Wiberg bond index in the transition state. All these were found to be in good agreement with the experimental findings.