- Effect of Temperature on the Enantioselectivity in the Oxazaborolidine-Catalyzed Asymmetric Reduction of Ketones. Noncatalytic Borane Reduction, a Nonneglectable Factor in the Reduction System
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The effect of temperature on the enantioselectivity of the oxazaborolidine-catalyzed asymmetric borane reduction of ketones has been investigated carefully using alkyl aryl ketones with a variety of functional groups and a B-methoxyoxazaborolidine derived from trimethyl borate and (S)-α,α-diphenylprolinol as a catalyst. The reductions were carried out over a range of temperatures in THF and toluene with or without the catalyst. The reductive rates increase along with increasing reaction temperature with or without the catalyst by determining the conversion of the ketones to alcohols by GC analysis. However, the rates of the catalytic reductions increase faster than those without the catalyst. The results indicate that the noncatalytic borane reduction is an important factor to the enantioselectivity in the reduction. The highest enantioselectivities were usually obtained between 20 and 30 °C in the asymmetric reduction.
- Xu, Jiaxi,Wei, Tiezheng,Zhang, Qihan
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Read Online
- Visible-Light-Driven Catalytic Deracemization of Secondary Alcohols
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Deracemization of racemic chiral compounds is an attractive approach in asymmetric synthesis, but its development has been hindered by energetic and kinetic challenges. Here we describe a catalytic deracemization method for secondary benzylic alcohols which are important synthetic intermediates and end products for many industries. Driven by visible light only, this method is based on sequential photochemical dehydrogenation followed by enantioselective thermal hydrogenation. The combination of a heterogeneous dehydrogenation photocatalyst and a chiral molecular hydrogenation catalyst is essential to ensure two distinct pathways for the forward and reverse reactions. These reactions convert a large number of racemic aryl alkyl alcohols into their enantiomerically enriched forms in good yields and enantioselectivities.
- Hu, Xile,Zhang, Zhikun
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supporting information
p. 22833 - 22838
(2021/09/09)
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- Chiral Frustrated Lewis Pairs Catalyzed Highly Enantioselective Hydrosilylations of Ketones
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A highly enantioselective Piers-type hydrosilylation of simple ketones was successfully realized using a chiral frustrated Lewis pair of tri-tert-butylphosphine and chiral diene-derived borane as catalyst. A wide range of optically active secondary alcohols were furnished in 80%—99% yields with 81%—97% ee's under mild reaction conditions.
- Liu, Xiaoqin,Wang, Qiaotian,Han, Caifang,Feng, Xiangqing,Du, Haifeng
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p. 663 - 666
(2019/05/21)
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- Asymmetric Magnesium-Catalyzed Hydroboration by Metal-Ligand Cooperative Catalysis
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Asymmetric catalysis with readily available, cheap, and non-toxic alkaline earth metal catalysts represents a sustainable alternative to conventional synthesis methodologies. In this context, we describe the development of a first MgII-catalyzed enantioselective hydroboration providing the products with excellent yields and enantioselectivities. NMR spectroscopy studies and DFT calculations provide insights into the reaction mechanism and the origin of the enantioselectivity which can be explained by a metal-ligand cooperative catalysis pathway involving a non-innocent ligand.
- Falconnet, Alban,Magre, Marc,Maity, Bholanath,Cavallo, Luigi,Rueping, Magnus
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supporting information
p. 17567 - 17571
(2019/11/13)
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- Co6H8(PiPr3)6: A Cobalt Octahedron with Face-Capping Hydrides
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A square-planar Co4amide cluster, Co4{N(SiMe3)2}4(2), and an octahedral Co6hydride cluster, Co6H8(PiPr3)6(4), were obtained from metathesis-type amide to hydride exchange reactions of a CoIIamide complex with pinacolborane (HBpin) in the absence/presence of PiPr3. The crystal structure of 4 revealed face-capping hydrides on each triangular [Co3] face, while the formal CoII2CoI4oxidation state of 4 indicated a reduction of the cobalt centers during the assembly process. Cluster 4 catalyzes the hydrosilylation of 2-cyclohexen-1-one favoring the conjugate reduction. Generation of the catalytically reactive Co cluster species was indicated by a trapping experiment with a chiral chelating agent.
- Ohki, Yasuhiro,Shimizu, Yuki,Araake, Ryoichi,Tada, Mizuki,Sameera,Ito, Jun-Ichi,Nishiyama, Hisao
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supporting information
p. 15821 - 15825
(2016/12/16)
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- Enantioselective Hydrosilylation of Ketones Catalyzed by a Readily Accessible N-Heterocyclic Carbene-Ir Complex at Room Temperature
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A series of functionalized azolium compounds were synthesized from chiral α-amino acid derivatives such as β-amino alcohols. of hydroxy-amide-functionalized azolium salts thus obtained with Ag2O afforded N-heterocyclic carbene-Ag (NHC-Ag) complexes. Subsequent treatment of the resulting silver compound with [IrCl(cod)]2 yielded monodentate IrCl(cod)(NHC), which was stable in air. The NHC-Ir complex facilitated efficient asymmetric hydrosilylation of ketones using (EtO)2MeSiH under ambient conditions. A chiral ligand containing an isobutyl stereodirecting group was found to be the best ligand for the functionalized NHC-Ir complexes that were examined. A linear relationship was found between the catalyst ee and the product ee. The hydroxy functional group on the NHC ligand side-arm not only induced stereocontrol but also enhanced the reaction rate.
- Shinohara, Kanako,Kawabata, Shun,Nakamura, Hanako,Manabe, Yoshiki,Sakaguchi, Satoshi
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p. 5532 - 5539
(2014/10/16)
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- Asymmetric hydrosilane reduction of ketones catalyzed by an iridium complex bearing a hydroxyamide-functionalized NHC ligand
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An enantioselective hydrosilylation of prochiral ketones was achieved by using a catalytic amount of the readily accessible and air- and moisture-stable iridium complex [IrCl(cod)(NHC)] at room temperature. Copyright
- Kawabata, Shun,Tokura, Hiromu,Chiyojima, Hiroyuki,Okamoto, Masaki,Sakaguchi, Satoshi
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experimental part
p. 807 - 812
(2012/05/04)
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- Iron- and cobalt-catalyzed asymmetric hydrosilylation of ketones and enones with bis(oxazolinylphenyl)amine ligands
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Chiral bis(oxazolinylphenyl)amines proved to be efficient auxiliary ligands for iron and cobalt catalysts with high activity for asymmetric hydrosilylation of ketones and asymmetric conjugate hydrosilylation of enones.
- Inagaki, Tomohiko,Phong, Le Thanh,Furuta, Akihiro,Ito, Jun-Ichi,Nishiyama, Hisao
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supporting information; experimental part
p. 3090 - 3096
(2010/08/05)
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- Preparative asymmetric reduction of ketones in a biphasic medium with an (S)-alcohol dehydrogenase under in situ-cofactor-recycling with a formate dehydrogenase
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The substrate range of a novel recombinant (S)-alcohol dehydrogenase from Rhodococcus erythropolis is described. In addition, an enzyme-compatible biphasic reaction medium for the asymmetric biocatalytic reduction of ketones with in situ-cofactor regeneration has been developed. Thus, reductions of poorly water soluble ketones in the presence of the alcohol dehydrogenase from R. erythropolis and a formate dehydrogenase from Candida boidinii can be carried out at higher substrate concentrations of 10-200 mM. The resulting (S)-alcohols were formed with moderate to good conversion rates, and with up to >99% ee.
- Gr?ger, Harald,Hummel, Werner,Rollmann, Claudia,Chamouleau, Francoise,Hüsken, Hendrik,Werner, Helge,Wunderlich, Christine,Abokitse, Kofi,Drauz, Karlheinz,Buchholz, Stefan
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p. 633 - 640
(2007/10/03)
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- Preparation of highly enantiomerically pure linear secondary alcohols via asymmetric reduction of prochiral ketones with borane
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An efficient and practical preparation of homochiral linear secondary alcohols, 1-(4-alkylphenyl) and 1-(4-alkoxylphenyl) alcohols, via the asymmetric oxazaborolidine-catalyzed borane reduction of prochiral ketones is described. The phenomenon of the enan
- Xu, Jiaxi,Su, Xianbin,Zhang, Qihan
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p. 1781 - 1786
(2007/10/03)
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- Studies on Rhizopus arrhizus mediated enantioselective reduction of arylalkanones
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The effect of substitution on the biotransformation of various arylalkanones using Rhizopus arrhizus was investigated. The organism was found to be promising for the reduction of phenylalkanones and arylethanones with good to excellent enantioselectivity. The reduction followed Prelog's rule giving the (S)-carbinols in all the cases. The enantioselectivity of the reaction improved with increasing size of the groups flanking the carbonyl function and the electron withdrawing capacity of the substituents in the aromatic ring. However, the yield was dramatically affected with increased hydrophobicity of the substrates.
- Salvi,Chattopadhyay
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p. 2833 - 2839
(2007/10/03)
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- ASYMMETRIC REDUCTION OF p-ALKYLACETOPHENONES
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Asymmetric reduction of p-alkylacetophenones Ia-VIIa with lithium aluminium hydride in the presence of (-)-quinine affords optically active alcohols Ib-VIIb of the (R)-(+) configuration in optical yields about 50 percent.
- Cervinka, Otakar,Fabryova, Anna,Brozova, Ivana,Holik, Miroslav
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p. 684 - 686
(2007/10/02)
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