title: Chiral 2,6-bis(oxazolinyl)pyridine-rare earth metal complexes as catalysts for highly enantioselective 1,3-dipolar cycloaddition reactions of 2-benzopyrylium-4-olates.
abstract: Significant levels of enantioselectivity were obtained in 1,3-dipolar cycloadditions of 2-benzopyrylium-4-olate generated from the Rh(2)(OAc)(4)-catalyzed decomposition of o-methoxycarbonyl-alpha-diazoacetophenone. This reaction utilized chiral 2,6-bis(oxazolinyl)pyridine (Pybox)--rare earth metal triflate complexes as chiral Lewis acid catalysts. The reactions with several benzyloxyacetaldehyde derivatives catalyzed by a Sc(III)--Pybox-i-Pr complex (10 mol %) proceeded smoothly to yield endo-adducts selectively with high enantioselectivity (up to 93% ee). For the reaction with benzyl pyruvate, the Sc(III)-Pybox-i-Pr complex (10 mol %) catalyzed the reaction effectively in the presence of trifluoroacetic acid (10 mol %) to yield an exo-adduct with both high diastereo- and enantioselectivity (94% ee). This catalytic system was efficiently applied to the reactions with several other alpha-keto esters with high exo- and enantioselectivities (up to 95% ee). In contrast to the reaction with carbonyl compounds, Yb(III)--Pybox-Ph complex (10 mol %) was found to be effective to obtain high enantioselectivity (96% ee) of diastereoselectively produced exo-cycloadduct in the reaction with 3-acryloyl-2-oxazolidinone.
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
authors.forename: Motoo
authors.initials: M
authors.lastname: Shiro
mesh_terms: D001685:Biological Factors / Q000737:chemistry; D002384:Catalysis; D004852:Epoxy Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008674:Metals, Rare Earth; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000032:analysis / Q000138:chemical synthesis* / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry; D012538:Scandium / Q000737:chemistry; D015018:Ytterbium / Q000737:chemistry
chemical_list: D001685:Biological Factors; D004852:Epoxy Compounds; D008674:Metals, Rare Earth; D009942:Organometallic Compounds; D011725:Pyridines; D012238:Rhodium; D015018:Ytterbium; D012538:Scandium