title: Highly enantioselective 1,3-dipolar cycloaddition reactions of 2-benzopyrylium-4-olate catalyzed by chiral Lewis acids.
abstract: We have found that significant levels of enantioselectivity are obtained in the 1,3-dipolar cycloadditions of 2-benzopyrylium-4-olate using chiral 2,6-bis(oxazolinyl)pyridine (Pybox)-rare earth metal triflate complexes as chiral Lewis acid catalysts. The reactions with benzyloxyacetaldehyde derivatives catalyzed by Sc(III)-Pybox-i-Pr (10 mol %) proceeded to give endo-adducts selectively with high enantioselectivity (up to 93% ee). The reaction with benzyl pyruvate under similar conditions gave an exo-adduct selectively with 87% ee. In the reaction with 3-acryloyl-2-oxazolidinone, Yb(III)-Pybox-Ph was found to be effective in providing an exo-adduct with extremely high enantioselectivity (98% ee).
authors.affiliation: Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, Wakasato, Nagano 380-8553, Japan. sugahio@gipwc.shinshu-u.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Suga
authors.forename: Kei
authors.initials: K
authors.lastname: Inoue
authors.forename: Shuichi
authors.initials: S
authors.lastname: Inoue
authors.forename: Akikazu
authors.initials: A
authors.lastname: Kakehi
mesh_terms: D000447:Aldehydes / Q000737:chemistry; D008698:Mesylates / Q000737:chemistry; D008674:Metals, Rare Earth; D010080:Oxazoles / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D011773:Pyruvates / Q000737:chemistry; D012538:Scandium / Q000737:chemistry; D013237:Stereoisomerism; D015019:Yttrium / Q000737:chemistry
chemical_list: D000447:Aldehydes; D008698:Mesylates; D008674:Metals, Rare Earth; D010080:Oxazoles; D011725:Pyridines; D011773:Pyruvates; C436603:scandium triflate; D015019:Yttrium; D012538:Scandium