- Syntheses and Crystal Structures of 4,5-Dihydro-2-(2'-hydroxyphenyl)oxazole-Containing Metal Complexes
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The synthesis of the complexes 3 of various metals ligated to chiral 4,5-dihydro-2-(2'-oxidophenyl-χO)oxazoles-χN is described (Scheme).Three of them, i.e. 3a, 3e, and 3f containing Cu(II), Zn(II), and Ni(II), respectively, were analyzed by X-ray diffract
- Bolm, Carsten,Weickhardt, Konrad,Zehnder, Margareta,Glasmacher, Dorothea
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- Reactions of m-chloroperoxybenzoic acid with dimeric cyclopalladated complexes derived from 2-phenyl-2-oxazolines
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Cyclopalladated complexes (CPCs) (S,S)-di-μ-Cl(κ2-C,N)2Pd2 (1a,b) and (S,S)-di-μ-OAc(κ2-C,N)2Pd2 (7a,b) obtained from (S)-4-t-butyl-(a) and (S)-4-ethyl-2-phenyl-2-oxazoline (b) were reacted
- Kukowski, Jonathan E.,Keuseman, Kristopher J.,Smoliakova, Irina P.
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- Alternatives to Phosphinooxazoline (t-BuPHOX) Ligands in the Metal-Catalyzed Hydrogenation of Minimally Functionalized Olefins and Cyclic β-Enamides
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This study presents a new series of readily accessible iridium- and rhodium-phosphite/oxazoline catalytic systems that can efficiently hydrogenate, for the first time, both minimally functionalized olefins and functionalized olefins (62 examples in total) in high enantioselectivities (ees up to >99%) and conversions. The phosphite-oxazoline ligands, which are readily available in only two synthetic steps, are derived from previous privileged 4-alkyl-2-[2-(diphenylphosphino)phenyl]-2-oxazoline (PHOX) ligands by replacing the phosphine moiety by a biaryl phosphite group and/or the introduction of a methylene spacer between the oxazoline and the phenyl ring. The modular design of the ligands has given us the opportunity not only to overcome the limitations of the iridium-PHOX catalytic systems in the hydrogenation of minimally functionalized Z-olefins and 1,1-disubstituted olefins, but also to expand their use to unfunctionalized olefins containing other challenging scaffolds (e.g., exocyclic benzofused and triaryl-substituted olefins) and also to olefins with poorly coordinative groups (e.g., α,β-unsaturated lactams, lactones, alkenylboronic esters, etc.) with enantioselectivities typically >95% ee. Moreover, both enantiomers of the hydrogenation product could be obtained by simply changing the configuration of the biaryl phosphite moiety. Remarkably, the new catalytic systems also provided excellent enantioselectivities (up to 99% ee) in the asymmetric hydrogenation of another challenging class of olefins – the functionalized cyclic β-enamides. Again, both enantiomers of the reduced amides could be obtained by changing the metal from Ir to Rh. We also demonstrated that environmentally friendly propylene carbonate can be used with no loss of enantioselectivity. Another advantage of the new ligands over the PHOX ligands is that the best ligands are derived from the affordable (S)-phenylglycinol rather than from the expensive (S)-tert-leucinol. (Figure presented.).
- Biosca, Maria,Magre, Marc,Coll, Mercè,Pàmies, Oscar,Diéguez, Montserrat
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p. 2801 - 2814
(2017/08/23)
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- PHOX-Based Phosphite-Oxazoline Ligands for the Enantioselective Ir-Catalyzed Hydrogenation of Cyclic Β-Enamides
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Simple Ir-PHOX-based phosphite-oxazoline catalysts have been successfully applied in the asymmetric hydrogenation of cyclic β-enamides providing better enantioselectivities than previous effective Ru and Rh catalysts. This protocol allows the synthesis of
- Magre, Marc,Pàmies, Oscar,Diéguez, Montserrat
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p. 5186 - 5190
(2016/08/18)
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- Synthesis of Air- and Moisture-Stable, Storable Chiral Oxorhenium Complexes and Their Application as Catalysts for the Enantioselective Imine Reduction
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Air-/moisture-stable, crystalline, and storable chiral salicyloxazoline based oxorhenium(V) complexes have been synthesized and their catalytic application for the asymmetric reduction of ketimines using hydrosilane as hydride source is disclosed. A broad substrate scope, high yields, and excellent enantioselectivities (up to 99 %) are attained. Furthermore, the syntheses of enantiopure α-amino esters, γ- and δ-lactams, and isoindolinones have also been carried out using this methodology. Finally, the method has been applied to synthetic targets of pharmaceutical relevance, such as R-(+)-salsolidine and R-(+)-crispine A.
- Das, Braja Gopal,Nallagonda, Rajender,Dey, Dhananjay,Ghorai, Prasanta
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p. 12601 - 12605
(2015/09/01)
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- Enantioselective Cu-catalyzed 1,4-addition of Me3 Al to a 4,4-disubstituted cyclohexa-2,5-dienone
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A series of chiral enantiomerically pure 2-aryloxazolines was synthesized. (4S)-2-(2',6'-dimethoxyphenyl)-4-isopropyloxazoline proved to be an efficient chiral ligand for the Cu-catalyzed conjugate addition of Me3Al to cyclohexadienone, and by using 20 mol% of this ligand, 1,4-adduct was obtained in 68% ee. In addition, TBDMSOTf is crucial for the asymmetric conjugate addition to proceed with good chemical yield and high ee.
- Takemoto, Yoshiji,Kuraoka, Satoru,Hamaue, Naoko,Aoe, Keiichi,Hiramatsu, Hajime,Iwata, Chuzo
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p. 14177 - 14188
(2007/10/03)
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