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Possible Catalytic Cycle (possible + catalytic_cycle)
Selected AbstractsLewis Basic Ionic Liquids-Catalyzed Conversion of Carbon Dioxide to Cyclic CarbonatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Zhen-Zhen Yang Abstract A series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives. Notably, quantitative yields together with excellent selectivity were attained when 1,8-diazabicyclo[5.4.0]undec-7-enium chloride ([HDBU]Cl) was used as a catalyst. Furthermore, the catalyst could be recycled over five times without appreciable loss of catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were investigated in detail. This protocol was found to be applicable to a variety of epoxides producing the corresponding cyclic carbonates in high yields and selectivity. Therefore, this solvent-free process thus represents an environmentally friendly example for the catalytic conversion of carbon dioxide into value-added chemicals by employing Lewis basic ionic liquids as catalyst. A possible catalytic cycle for the hydrogen bond-assisted ring-opening of epoxide and activation of carbon dioxide induced by the nucleophilic tertiary nitrogen of the ionic liquid was also proposed. [source] Enantioselective Synthesis of Chiral Tetrahydroisoquinolines by Iridium-Catalyzed Asymmetric Hydrogenation of EnaminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Pu-Cha Yan Abstract Chiral iridium complexes based on spiro phosphoramidite ligands are demonstrated to be highly efficient catalysts for the asymmetric hydrogenation of unfunctionalized enamines with an exocyclic double bond. In combination with excess iodine or potassium iodide and under hydrogen pressure, the complex Ir/(Sa,R,R)- 3a provides chiral N -alkyltetrahydroisoquinolines in high yields with up to 98% ee. The L/Ir ratio of 2:1 is crucial for obtaining a high reaction rate and enantioselectivity. A deuterium labeling experiment showed that an inverse isotope effect exists in this reaction. A possible catalytic cycle including an iridium(III) species bearing two monophosphoramidite ligands is also proposed. [source] Highly Enantioselective Allylation of Aromatic ,-Keto Phosphonates Catalyzed by Chiral N,N,- Dioxide-Indium(III) ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2 2008Jinglun Huang Abstract The ramipril derivative N,N, -dioxide 3g -indium(III) complex was found to be an efficient catalyst for the allylation of the aromatic ,-keto phosphonates. The corresponding ,-hydroxy phosphonates were obtained with high yields (up to 98,%) and high enantioselectivities (up to 91,% ee). A bifunctional catalyst system was described with an N -oxide as Lewis base activating tetraallyltin and indium as Lewis acid activating aromatic ,-keto phosphonates. A possible catalytic cycle has been proposed to explain the mechanism of the reaction. [source] Catalytic Asymmetric Synthesis of 3-(,-Hydroxy-,-carbonyl) Oxindoles by a ScIII -Catalyzed Direct Aldol-Type ReactionCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2010Ke Shen Abstract A direct catalytic asymmetric aldol-type reaction of 3-substituted-2-oxindoles with glyoxal derivatives and ethyl trifluoropyruvate, catalyzed by a chiral N,N, -dioxide,Sc(OTf)3 (Tf=trifluoromethanesulfonyl) complex, has been developed that tolerates a wide range of substrates. The reaction proceeds in good yields and excellent enantioselectivities (up to 93,% yield, 99:1 diastereomeric ratio (dr), and >99,% enantiomeric excess (ee)) under mild conditions, to deliver 3-(,-hydroxy-,-carbonyl) oxindoles with vicinal quaternary,tertiary or quaternary,quaternary stereocenters. Even with 1,mol,% catalyst loading or on scaleup (10,mmol of starting material), maintenance of ee was observed, which showed the potential value of the catalyst system. In studies probing the reaction mechanism, a positive nonlinear effect was observed and ScIII -based enolate intermediates were detected by using ESIMS. On the basis of the experimental results and previous reports, a possible catalytic cycle was assumed. [source] | ||||||||||