title: Asymmetric 1,3-dipolar cycloadditions of N-benzyl and N-diphenylmethyl nitrones and alpha,beta-unsaturated aldehydes catalyzed by bis-titanium chiral Lewis acids.
abstract: Bis-titanium chiral Lewis acids that contain two oxygen-bridged titanium centers were successfully applied to the asymmetric 1,3-dipolar cycloaddition of nitrones and alpha,beta-unsaturated aldehydes. The introduction of the diphenylmethyl group as the N substituent on the nitrones, with the aim of destabilizing the nitrone-Lewis acid complex, led to the drastic enhancement of not only the reactivity but also the enantioselectivity. By employing this approach, 1,3-dipolar cycloadditions of nitrones and the rather unreactive methacrolein were facilitated to give cycloadducts that bear one all-carbon quaternary center with unique regioselectivity and excellent stereoselectivity.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Hashimoto
authors.forename: Masato
authors.initials: M
authors.lastname: Omote
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Hato
authors.forename: Taichi
authors.initials: T
authors.lastname: Kano
authors.forename: Keiji
authors.initials: K
authors.lastname: Maruoka