Asymmetric Epoxidation of Enones by Peptide-Based Catalyst: A Strategy Inverting Julia-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-LeuAib) 2 (Aib: 2-aminoisobutyric acid). This peptide successfully catalyzed the asymmetric epoxidation of a-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.