On the Mechanism of Asymmetric Epoxidation of Enones Catalyzed by α,α-L-Diarylprolinols: A Theoretical Insight

The mechanism of the asymmetric epoxidation of enones with tert-butyl hydroperoxide promoted by a,a-L-diarylprolinols has been studied by second order MollerPlesset perturbation theory (MP2) and density functional theory (DFT) computations. The non-covalent activation of the reactants, through an effective network of hydrogen bonding interactions, initially hypothesized on the basis of the available experimental data, is shown to constitute an energetically viable pathway. According to the non-covalent route, the reaction follows a two-step nucleophilic epoxidation mechanism, with the first oxa-Michael addition being the rate- and stereoselectivity-determining step. Formation of the (2R,3S)-enantiomer of the epoxide derived from trans-chalcone is predicted to be energetically favoured, in agreement with the experimental findings.