title: Highly Enantioselective Bromocyclization of Allylic Amides with a P/P=O Double-Site Lewis Base Catalyst.
abstract: The enantioselective bromocyclization of allylic amides catalyzed by phosphorus-containing Lewis bases was examined in detail. A series of control experiments and NMR studies showed that a partially oxidized bis-phosphine generated in situ serves as the actual enantioselective catalyst. The reaction mechanism involves distinct roles of two Lewis basic sites, P and P=O, with P+Br serving as a fine-tuning element for substrate fixation in the chiral environment, and P+OBr as the Br+transfer agent to the olefin. Catalyst loading could be reduced to as little as 1 mol %, and the reaction affords enantioenriched oxazolines with up to >99.5 % ee.
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kawato
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Ono
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan.
authors.forename: Akino
authors.initials: A
authors.lastname: Kubota
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nagao
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Morita
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan.
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Egami
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526, Japan. hamashima@u-shizuoka-ken.ac.jp.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Hamashima
keywords: Lewis bases; asymmetric catalysis; cyclization; phosphine oxides; phosphines