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Excellent Enantioselectivities (excellent + enantioselectivity)
Selected AbstractsEnhanced Cooperativity in Hydrolytic Kinetic Resolution of Epoxides using Poly(styrene) Resin-Supported Dendronized Co-(Salen) CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2008Poorva Goyal Abstract Excellent enantioselectivities and isolated yields have been achieved for the hydrolytic kinetic resolution of epoxides using a resin-supported dendronized R,R-(salen)Co catalyst with catalyst loadings as low as 0.04 mol%, the lowest metal loadings of any heterogeneous resin-supported (salen)Co catalyst reported to date. In addition, the supported catalysts can be recycled and reused with comparable enantioselectivities. It is hypothesized that the high catalytic activity can be attributed to the flexible linker and the dendronized framework supporting the (salen)Co moieties on the resin thereby promoting cooperativity between two metal centers. This work opens up new opportunities for the design of highly active resin-supported catalysts that catalyze transformations through a bimetallic pathway. [source] Norbornene Bidentate Ligands: Coordination Chemistry and Enantioselective Catalytic ApplicationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2010Fernando Fernández Abstract N - and P-donor derivatives have been prepared by functionalization of a readily available norbornene precursor. Palladium catalytic systems containing these new ligands were applied in allylic substitution, and yielded high activities and excellent enantioselectivities for the allylic alkylation and amination reactions (ee up to 97,%). A full coordination analysis of the catalytic precursors including modelling studies was also carried out. [source] Synthesis of Binaphthyl Sulfonimides and Their Application in the Enantioselective Michael Addition of Ketones to NitroalkenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2010Shurong Ban Abstract Novel types of L -proline-based binaphthyl sulfonimides and sulfonamides were found to be efficient organocatalysts for the asymmetric Michael addition of ketones to nitroalkenes to provide optically active ,-nitroketone derivatives of synthetic and biological importance. After the fine optimization of solvents, temperature, and additive, good to excellent enantioselectivities and diastereoselectivities (71,96,%,ee, up to >99:1,dr) can be achieved. [source] Enantioselective Michael Addition of Aromatic Ketones to Nitroolefins Catalyzed by Bifunctional Thioureas and Mechanistic InsightEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2010Bai-Lin Li Abstract A highly enantioselective Michael reaction of aromatic ketones with nitroolefins was accomplished in the presence of a chiral bifunctional primary amine,thiourea catalyst and 4-nitrobenzoic acid as the co-catalyst; the corresponding adducts were obtained in excellent enantioselectivities (up to 99,%,ee) and yields (up to 98,%). The catalytic mechanism of the Michael reaction was confirmed through the ESI-MS detection of proposed reaction intermediates and the 1H NMR detection of hydrogen bonding between thiourea and the nitroolefins. DFT calculations showed that chiral moieties of the thiourea impacted the yields and enantioselectivities of the adducts remarkably, which corresponds to the observed experimental results. [source] Polymer-Immobilized Pyrrolidine-Based Chiral Ionic Liquids as Recyclable Organocatalysts for Asymmetric Michael Additions to Nitrostyrenes under Solvent-Free Reaction ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2008Pinhua Li Abstract A polymer immobilized pyrrolidine-based chiral ionic liquid 5a was synthesized and was found to be a highly efficient catalyst for the Michael additions of ketones and aldehydes to nitrostyrenes, which afforded the corresponding adducts in good yields (up to 97,%), excellent enantioselectivities (up to >99,% ee) and high diastereoselectivities (up to >99:1 dr) under solvent-free reaction conditions. In addition, the catalyst 5a could be reused at least eight times without a significant loss of its catalytic activity and stereoselectivity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] 2-[(Imidazolylthio)methyl]pyrrolidine as a Trifunctional Organocatalyst for the Highly Asymmetric Michael Addition of Ketones to NitroolefinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2008Dan-Qian Xu Abstract The direct asymmetric Michael addition of ketones to nitroolefins catalyzed by 2-[(imidazol-2-ylthio)methyl]pyrrolidine, constructed from natural L -proline and imidazolylthio platforms, with salicylic acid as a co-catalyst has been developed to give the products in high yields (up to 95,%) and with excellent enantioselectivities (up to 99,% ee). The highly efficient catalytic performance may be attributed to the dual activation of the Michael substrates by the trifunctional organocatalysts and the co-catalyst salicylic acid, leading to the formation of a stable transition state complex through the synergic effect of hydrogen-bonding and electrostatic interactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Enantioselective One-Pot Two-Step Synthesis of Hydrophobic Allylic Alcohols in Aqueous Medium through the Combination of a Wittig Reaction and an Enzymatic Ketone ReductionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2007Marina Kraußer Abstract A one-pot two-step process for the enantioselective synthesis of hydrophobic allylic alcohols was developed, which comprises ketone formation by the Wittig reaction and their enzymatic in situ biotransformation into the desired target products. By means of this combined Wittig reaction and bioreduction, the allylic alcohols were prepared with conversions of up to 90,%, and with excellent enantioselectivities of >99,% ee. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Complete Chiral Induction from Enantiopure 1,2-Diamines to Benzophenone-Based Achiral Bisphosphane Ligands in Noyori-Type RuII CatalystsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2006Qing Jing Abstract We report the design and synthesis of a novel class of RuII catalysts (3) composed of achiral benzophenone-based bisphosphane ligands and enantiopure 1,2-diamines for the asymmetric hydrogenation of aryl ketones. The developed catalysts show excellent enantioselectivities (up to 97,% ee) and activities (up to S/C = 10,000) in the hydrogenation of a variety of aromatic ketones.Complete chiral induction from the enantiopure 1,2-diamine to the achiral bisphosphane ligand was observed. The coordination of the C=O moiety in 3 to the cationic RuII center is considered to be of key importance in providing a higher thermodynamic and kinetic rotation barrier for the flexible bisphosphane ligand, resulting in the preferential formation of only one diastereomer, and thus explaining the high enantioselectivity of the catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Enantioselective Synthesis of , -Blockers via Hydrolytic Kinetic Resolution of Terminal Oxiranes by Using Bimetallic Chiral {{2,2,-[Cyclohexane-1,2-diylbis(nitrilomethylidyne)]bis[phenolato]}(2,)}cobalt ([Co(salen)])-Type ComplexesHELVETICA CHIMICA ACTA, Issue 2 2008Rahul Abstract The synthesis of chirally pure , -blockers was successfully achieved via hydrolytic kinetic resolution of butyl (±)-4-(oxiran-2-ylmethoxy)benzeneacetate ((±)- 1) and (±)-4-(oxiran-2-ylmethoxy)benzeneacetonitrile ((±)- 2) in the presence of bimetallic chiral [Co(salen)]-type complexes. The newly synthesized bimetallic chiral [Co(salen)]-type complexes exhibited excellent enantioselectivities of up to >98% ee in good yields (Tables,1,3). [source] An Organocatalytic Domino Thia-Michael/Aldol Condensation Reaction: Highly Enantioselective Synthesis of Functionalized DihydrothiophenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Jie Tang Abstract An organocatalytic domino thia-Michael/aldol condensation reaction of ,, ,-unsaturated aldehydes with 1, 4-dithiane-2,5-diol catalyzed by chiral diphenylprolinol TMS ether has been developed, which provides a new practical and direct route to chiral dihydrothiophenes with high yields (up to 90%) and excellent enantioselectivities (up to>99% ee). The catalytic mechanism of the domino reaction was further confirmed through the APCI-MS detection of proposed reaction intermediates. [source] Enantioselective Organocatalytic Transfer Hydrogenation of ,-Imino Esters by Utilization of Benzothiazoline as Highly Efficient Reducing AgentADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Chen Zhu Abstract Benzothiazoline was employed as an efficient and versatile reducing agent for the chiral phosphoric acid-catalyzed transfer hydrogenation of ,-imino esters. The corresponding ,-amino esters were furnished with excellent enantioselectivities. Novel and readily removable benzothiazolines bearing a hydroxy group were also investigated. [source] Highly Enantioselective One-Pot Copper-Catalyzed 1,4 Addition/Organocatalyzed ,-Substitution of EnalsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Adrien Quintard Abstract The asymmetric copper-catalyzed addition of dialkylzinc to enals followed by organocatalyzed one-pot aldehyde ,-functionalization has been accomplished providing CC, CCl or CF bond formation. These simple procedures led to the creation of two contiguous stereocenters in excellent enantioselectivities (typical ee=99%). This methodology has been applied in the synthesis of (2S,3S) isomer of Valnoctamide®. [source] Iridium-Difluorphos-Catalyzed Asymmetric Hydrogenation of 2-Alkyl- and 2-Aryl-Substituted Quinoxalines: A General and Efficient Route into TetrahydroquinoxalinesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Damien Cartigny Abstract A highly efficient and general iridium-difluorphos-catalyzed asymmetric hydrogenation of diverse 2-alkyl- and 2-aryl-substituted quinoxalines into biologically and pharmaceutically relevant 2-substituted-1,2,3,4-tetrahydroquinoxaline units has been developed. High isolated yields and excellent enantioselectivities of up to 95% for 2-alkyl-substituted quinoxalines and of up to 94% for 2-aryl-substituted quinoxalines were obtained. [source] Enantioselective Synthesis of Spirocyclic Oxindole-,-lactones via N-Heterocyclic Carbene-Catalyzed Cycloaddition of Ketenes and IsatinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Xiao-Na Wang Abstract Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [2+2] cycloaddition reaction of disubstituted ketenes and isatins to give the corresponding spirocyclic oxindole-,-lactones in good yields with good diastereoselectivities and excellent enantioselectivities. Ring opening with Grignard reagents or decarboxylation of the oxindole spirocyclic-,-lactone gave the corresponding 3-hydroxy- or 3-alkylenyloxindoles in good yields. [source] A General Approach to the Synthesis of ,2 -Amino Acid Derivatives via Highly Efficient Catalytic Asymmetric Hydrogenation of ,-AminomethylacrylatesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Yujuan Guo Abstract A new strategy was developed for the synthesis of a valuable class of ,-aminomethylacrylates via the Baylis,Hillman reaction of different aldehydes with methyl acrylate followed by acetylation of the resulting allylic alcohols and SN2,-type amination of the allylic acetates. Asymmetric hydrogenation of these diverse olefinic precursors using rhodium(Et-Duphos) catalysts provided the corresponding ,2 -amino acid derivatives with excellent enantioselectivities and exceedingly high reactivities (up to >99.5% ee and S/C=10,000). The first hydrogenation of (Z)-configurated substrates was studied for the synthesis of ,2 -amino acid derivatives. The high influence of the substrate geometry and steric hindrance on the reactivity and enantioselectivity was also disclosed for this reaction. This protocol provides a highly practical, facile and scalable method for the preparation of optically pure ,2 -amino acids and their derivatives under mild reaction conditions. [source] Palladium(II) Complexes of C2 -Bridged Chiral Diphosphines: Application to Enantioselective Carbonyl-Ene ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8 2010He-Kuan Luo Abstract (11bR,11,bR)-4,4,-(1,2-Phenylene)bis[4,5-dihydro-3H -dinaphtho[2,1- c:1,,2,- e]phosphepin] [abbreviated as (R)-BINAPHANE], (3R,3,R,4S,4,S,11bS,11,bS)-4,4,-bis(1,1-dimethylethyl)-4,4,,5,5,-tetrahydro-3,3,-bi-3H -dinaphtho[2,1- c:1,,2,- e]phosphepin [(S)-BINAPINE], (1S,1,S,2R,2,R)-1,1,-bis(1,1-dimethylethyl)-2,2,-biphospholane [(S,S,R,R)-TANGPHOS] and (2R,2,R,5R,5,R)-1,1,-(1,2-phenylene)bis[2,5-bis(1-methylethyl)phospholane] [(R,R) -i- Pr-DUPHOS] are C2 -bridged chiral diphosphines that form stable complexes with palladium(II) and platinum(II) containing a five-membered chelate ring. The Pd(II)-BINAPHANE catalyst displayed good to excellent enantioselectivities with ee values as high as 99.0% albeit in low yields for the carbonyl-ene reaction between phenylglyoxal and alkenes. Its Pt(II) counterpart afforded improved yields while retaining satisfactory enantioselectivity. For the carbonyl-ene reaction between ethyl trifluoropyruvate and alkenes, the Pd(II)-BINAPHANE catalyst afforded both good yields and extremely high enantioselectivities with ees as high as 99.6%. A comparative study on the Pd(II) catalysts of the four C2 -bridged chiral diphosphines revealed that Pd(II)-BINAPHANE afforded the best enantioselectivity. The ee values derived from Pd(II)-BINAPHANE are much higher than those derived from the other three Pd(II) catalysts. A comparison of the catalyst structures shows that the Pd(II)-BINAPHANE catalyst is the only one that has two bulky (R)-binaphthyl groups close to the reaction site. Hence it creates a deep chiral space that can efficiently control the reaction behavior in the carbonyl-ene reactions resulting in excellent enantioselectivity. [source] Highly Enantioselective Michael Addition Reactions of 3-Substituted Benzofuran-2(3H)-ones to Chalcones Catalyzed by a Chiral Alkyl-Substituted ThioureaADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010Xin Li Abstract A highly enantioselective Michael addition of 3-substituted benzofuran-2(3H)-ones to chalcones catalyzed by a chiral bifunctional thiourea was developed. Several chiral 3,3,-substituted benzofuran-2(3H)-ones derivatives, bearing adjacent quaternary-tertiary stereocenters, were efficiently synthesized with excellent enantioselectivities. [source] Development of Diphenylamine-Linked Bis(imidazoline) Ligands and Their Application in Asymmetric Friedel,Crafts Alkylation of Indole Derivatives with NitroalkenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010Han Liu Abstract The new diphenylamine-linked bis(imidazoline) ligands were prepared through Kelly-You's imidazoline formation procedure mediated by Hendrickson's reagent in good yields. The novel ligands were tested in the asymmetric Friedel,Crafts alkylation of indole derivatives with nitroalkenes. In most cases, good yields (up to 97%) and excellent enantioselectivities (up to 98%) can be achieved. The optimized bis(imidazoline) ligand with trans -diphenyl substitution on the imidazoline ring gave better enantioselectivity than the corresponding bis(oxazoline) ligand. [source] Highly Efficient Asymmetric Three-Component Vinylogous Mannich Reaction Catalyzed by a Chiral Scandium(III)- N,N,-Dioxide ComplexADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Qi Zhang Abstract The asymmetric three-component vinylogous Mannich reaction of an acyclic silyl dienol ester, an aldehyde and 2-aminophenol was accomplished using a chiral N,N,-dioxide-scandium(III) complex as the catalyst. A variety of aldehydes were found to be suitable substrates for the reaction and the desired ,-amino-,,,-unsaturated esters were obtained in 90,99% yields with good to excellent enantioselectivities (up to >99% ee) and complete regioselectivities. Moreover, the simple experimental procedures were air-tolerant and convenient. The present catalytic process provides the potential for large-scale syntheses of the chiral ,-amino-,,,-unsaturated esters. [source] Organocatalytic Asymmetric Michael Addition of Pyrazolin-5-ones to Nitroolefins with Bifunctional Thiourea: Stereocontrolled Construction of Contiguous Quaternary and Tertiary StereocentersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010Yu-Hua Liao Abstract The first organocatalytic diastereo- and enantioselective Michael addition reaction of 4-substituted-pyrazolin-5-ones to nitroolefins has been developed with a chiral bifunctional thiourea as organocatalyst. A wide variety of desired multi-substituted pyrazolin-5-one derivatives with contiguous quaternary and tertiary stereocenters are smoothly obtained in very good yields (up to 98%) with excellent enantioselectivities (up to>99% ee) and acceptable diastereoselectivities (up to 80:20). This experimentally simple process facilitates the access to various enantioenriched, multiply substituted pyrazolin-5-one derivatives, potential biologically active molecules, starting from readily available starting materials. [source] Imidazolium Ion-Tagged Proline Organocatalyst for ,-Aminoxylation of Aldehydes and Ketones in Ionic LiquidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Xiong Ding Abstract A novel imidazolium ion-tagged L -proline catalyst has been developed. The asymmetric ,-aminoxylation of aldehydes and ketones with excellent enantioselectivities, up to 99% ee, and high yields in ionic liquids has been achieved. The system can be easily recycled and reused for at least six times without significant loss of yields and enantioselectivity. [source] Highly Efficient and Enantioselective Iridium-Catalyzed Asymmetric Hydrogenation of N -AryliminesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Wei Li Abstract A catalytic method employing the cationic iridium-(Sc,Rp)-DuanPhos [(1R,1,R,2S,2,S)-2,2,-di- tert -butyl-2,2,,3,3, -tetrahydro-1H,1,H -1,1,-biisophosphindole] complex and BARF {tetrakis[3,5-bis(trifluoromethyl)phenyl]borate} counterion effectively catalyzes the enantioselective hydrogenation of acyclic N -arylimines with high turnover numbers (up to 10,000 TON) and excellent enantioselectivities (up to 98% ee), achieving the practical synthesis of chiral secondary amines. [source] Enantioselective Synthesis of Dihydrocoumarins via N-Heterocyclic Carbene-Catalyzed Cycloaddition of Ketenes and o -Quinone MethidesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Hui Lv Abstract Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [4+2],cycloaddition reaction of alky(aryl)ketenes and o -quinone methides to give the corresponding 3,3,4-trisubstituted 3,4-dihydrocoumarins in good yields with good diastereoselectivities and excellent enantioselectivities. [source] Enantio- and Diastereoselective Mannich-Type Reactions of ,-Cyano Ketones with N -Boc Aldimines Catalyzed by Chiral Bifunctional UreaADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Ju Hee Lee Abstract The catalytic enantioselective electrophilic Mannich-type reaction promoted by chiral bifunctional organocatalysts is described. The treatment of ,-cyano ketones with N -Boc-aldimines under mild reaction conditions afforded the corresponding ,-amino-,-cyano ketones with excellent diastereoselectivities (up to syn/anti=100/0), and excellent enantioselectivities (up to 99% ee). [source] Highly Efficient Organocatalyzed Direct Asymmetric Aldol Reactions of Hydroxyacetone and AldehydesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Xiaoyu Wu Abstract Novel organocatalysts derived from L -threonine and L -leucine have been synthesized for catalyzing direct aldol reactions of hydroxycetone and unactivated aliphatic aldehydes with as low as 2,mol% loading of the catalyst, good to excellent yields and excellent enantioselectivities have been achieved for aliphatic aldehydes, whereas aromatic aldehydes yield only moderate enantioselectivities. [source] New efficient copper fluoride-based catalyst for enantioselective hydrosilylation of ketones in aerobic conditionsISRAEL JOURNAL OF CHEMISTRY, Issue 4 2001James Courmarcel A new copper(II) fluoride,chiral diphosphines catalytic system was developed. This one is very efficient and selective for the hydrosilylation of several substituted or unsubstituted aromatic ketones in so far as moderate to excellent enantioselectivities were obtained. An oxygen acceleration effect was observed that led us to propose a practical protocol with a low amount of catalyst. [source] The Synthesis of Spirobitetraline Phosphoramidite Ligands and their Application in Rhodium-Catalyzed Asymmetric HydrogenationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2007Xiang-Hong Huo Abstract A racemic 1,1, - spirobitetralin-8,8,-diol (SBITOL) was conveniently synthesized from 3-methoxybenzaldehyde in 26,% yield over 9 steps and resolved via its bis-(S)-camphorsulfonates. The corresponding chiral spirobitetraline monophosphoramidite ligands have been prepared and their rhodium complexes were applied in the asymmetric hydrogenation of dehydroamino esters with good to excellent enantioselectivities (up to 99.3,% ee). [source] Chiral Phosphoric Acid-Catalyzed Enantioselective Aza-Friedel,Crafts Reaction of IndolesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2007Masahiro Terada Abstract A highly enantioselective 1,2-aza-Friedel,Crafts reaction of N - tert -butyldimethylsilylindole with N - tert -butoxycarbonyl aromatic imines is demonstrated using a BINOL-derived monophosphoric acid catalyst. The present approach provides efficient access to 3-indolylmethaneamines with aryl substituents in excellent enantioselectivities (up to 98,% ee). An inversion in the sense of enantioselection was found between monophosphoric acid catalysts bearing different substituents introduced at the 3,3,-position of binaphthyl backbone. We also calculated the three-dimensional structure of the monophosphoric acid catalysts to speculate on the inversion of the stereochemical outcome. [source] Synthesis of Diastereomeric 1,4-Diphosphine Ligands Bearing Imidazolidin-2-one Backbone and Their Application in Rh(I)-Catalyzed Asymmetric Hydrogenation of Functionalized OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2005Jian Zhang Abstract The diastereomeric 1,4-diphosphine ligands, (S,S,S,S)- 1a, (R,S,S,R)- 1b and (R,S,S,S)- 1c, with the imidazolidin-2-one backbone were synthesized, and utilized for an investigation of the effects of backbone chirality on the enantioselectivity in the Rh(I)-catalyzed hydrogenation of various functionalized olefinic substrates. It was found that the catalytic efficiencies are largely dependent on the configurations of the ,-carbons to phosphine. Thus, the Rh complex of the pseudo- C2 -symmetrical diphosphine, (R,S,S,S)- 1c, showed excellent enantioselectivities (93.0,98.6% ees) in the hydrogenations of a broad spectrum of substrates, and especially in the hydrogenations of methyl ,-(N -acetyamino)-,-arylacrylates (95.3,97.0% ees). However, the enantioselectivities obtained with the C2 -symmetrical (R,S,S,R)- 1b were largely dependent on the substrate (19.8,97.3% ees). The Rh complex of ligand 1a having the (S,S,S,S)-configuration showed the lowest catalytic efficiency for all of the substrates examined (0,84.8% ees). [source] ChemInform Abstract: Highly Efficient Dynamic Kinetic Resolution of Secondary Aromatic Alcohols with Low-Cost and Easily Available Acid Resins as Racemization Catalysts.CHEMINFORM, Issue 32 2010Yongmei Cheng Abstract A combination of Novozym435 with an acidic polystyrene resin CD8604 affords a new and efficient dynamic kinetic resolution of acetophenones to give the corresponding benzylic alcohols with good to excellent enantioselectivities. [source] | ||||||||||||||||||||||