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

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 l -3-(1-pyrenyl)alanine, a non-natural amino acid with a bulky side chain, which is connected to l -proline and then to 310-helical ( l -Leu- l -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 Julia–Colonna reaction, oligo- l -Leu-catalyzed epoxidation of enones, while both of the peptide catalysts consist of l -amino acids.