Asymmetric Epoxidation of Enones by Peptide-Based Catalyst: A Strategy Inverting Juliá–Colonna Stereoselectivity

Abstract

A resin-supported peptide catalyst with an N-terminal primary amino group was developed for asymmetric epoxidation of enones through iminium activation. The peptide has N-terminal <sc>l</sc>-3-(1-pyrenyl)alanine, a non-natural amino acid with a bulky side chain, which is connected to <sc>l</sc>-proline and then to 3₁₀-helical (<sc>l</sc>-Leu-<sc>l</sc>-Leu-Aib)₂ (Aib: 2-aminoisobutyric acid). This peptide successfully catalyzed the asymmetric epoxidation of β-aryl-substituted enones with electron-withdrawing groups on the aryl group. The feature of the present peptide catalyst is that the sense of the enantioselectivity is opposite to that of Juliá–Colonna reaction, oligo-<sc>l</sc>-Leu-catalyzed epoxidation of enones, while both of the peptide catalysts consist of <sc>l</sc>-amino acids.