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

Abstract

The mechanism of the asymmetric epoxidation of enones with tert-butyl hydroperoxide promoted by a,a-l-diarylprolinols has been studied by second order Møller-Plesset 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.

DFT predictions of the oxidation potential of organic dyes for opto-electronic devices

“…To approach the problematic task of evaluating Gibbs free energies in solution with quantum chemical computations [46,47], the term in square brackets in Eq. (2) is usually determined by using a thermodynamic cycle (Fig.…”

Organocatalysts for enantioselective synthesis of fine chemicals: definitions, trends and developments

“…For the first organocatalytic addition of benzotriazole (58) to the enone 57, the authors hypothesise an H-bond network acting in the transition state towards the induction of a moderate enantioselectivity in the subsequent formation of the product 59. The group of Lattanzi, in the last decade achieved very good results in the epoxidation of electron deficient alkenes, such as enones and acrylonitriles, in addition to some elucidations on the reaction mechanism, which confirm the hypothesis of an H-bonding catalysis [65]. Furthermore, some interesting results have been achieved in the epoxidation of α-ylidenoxindoles, which are electron-poor alkenes bearing an oxindole core.…”

Organocatalysts for enantioselective synthesis of fine chemicals: definitions, trends and developments

“…For the first organocatalytic addition of benzotriazole (49) to the enone 48, the authors hypothesize a hydrogen bond network acting in the transition state towards the induction of a moderate enantioselectivity in the subsequent formation of the product 50. The group of Lattanzi in the last decade achieved very good results in the epoxidation of electron deficient alkenes, such as enones and acrylonitriles, in addition to some elucidations on the reaction mechanism, which confirm the hypothesis of a hydrogen bond catalysis [69]. Furthermore, some interesting results have been achieved in the epoxidation of α-ylidenoxindoles, which are electron-poor alkenes bearing an oxindole core.…”