title: Design of new chiral phase-transfer catalysts with dual functions for highly enantioselective epoxidation of alpha,beta-unsaturated ketones.
abstract: A new chiral ammonium bromide, 1-Br, possessing diarylmethanol functionality as a substrate recognition site has been designed as a promising, dual-functioning catalyst for the highly enantioselective epoxidation of alpha,beta-unsaturated ketones under mild phase-transfer conditions. For instance, vigorous stirring of a mixture of chalcone, 1-Br (3 mol %), and 13% NaOCl in toluene at 0 degrees C for 24 h gave rise to epoxy chalcone quantitatively with 96% ee. A variety of alpha,beta-unsaturated ketones can also be epoxidized with rigorous stereochemical control, clearly demonstrating the effectiveness and utility of the present system. Further, a successful single-crystal X-ray diffraction analysis of 1-PF6 uncovered its distinctive three-dimensional molecular architecture and provided useful information for postulating the transition state.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ooi
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ohara
authors.forename: Masazumi
authors.initials: M
authors.lastname: Tamura
authors.forename: Keiji
authors.initials: K
authors.lastname: Maruoka