title: Transition state studies on the dioxirane-mediated asymmetric epoxidation via kinetic resolution and desymmetrization.
abstract: This paper describes an efficient kinetic resolution process of trisubstituted cyclic olefins via a chiral dioxirane generated in situ from a fructose-derived ketone and Oxone. The substrates presented include a variety of 1,3-disubstituted and 1,6-disubstituted cyclohexenes with the stereogenic centers at allylic positions. A sequential desymmetrization and kinetic resolution of 1,4-cyclohexadienes by the chiral dioxirane was also found to be feasible. The initially formed monoepoxides can be kinetically resolved by continuing the reaction, leading to the increase or decrease of the ee values of monoepoxides depending on the diene systems. In some cases, a prochiral directing group is not required and the first formed epoxide stereoselectively directs the second epoxidation. When the coupled desymmetrization and kinetic resolution is used synergistically, high enantiopurity can be obtained for an epoxide from an intrinsically less enantioselective substrate. The observed absolute and relative stereochemistry as well as the changing optical purity can be effectively rationalized by transition state analysis.
authors.affiliation: Department of Chemistry, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Jon C
authors.initials: JC
authors.lastname: Lorenz
authors.forename: Michael
authors.initials: M
authors.lastname: Frohn
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Zhou
authors.forename: Jian-Rong
authors.initials: JR
authors.lastname: Zhang
authors.forename: Yong
authors.initials: Y
authors.lastname: Tang
authors.forename: Christopher
authors.initials: C
authors.lastname: Burke
authors.forename: Yian
authors.initials: Y
authors.lastname: Shi
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D004852:Epoxy Compounds / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry; D007700:Kinetics; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D004852:Epoxy Compounds; D007659:Ketones; C061799:dioxirane