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Asymmetric Aldol Reaction (asymmetric + aldol_reaction)
Kinds of Asymmetric Aldol Reaction Selected AbstractsEnhanced Activity and Stereoselectivity of Polystyrene-Supported Proline-Based Organic Catalysts for Direct Asymmetric Aldol Reaction in WaterEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2009Michelangelo Gruttadauria Abstract Several polystyrene-supported proline dipeptides and a prolinamide derivative were prepared by thiol,ene coupling. These materials were used as catalysts for the direct asymmetric aldol reaction in water, and results compared with unsupported catalysts in water. Such an approach gave more active or stereoselective catalysts compared to the unsupported compounds, showing that our immobilization procedure may be useful to develop catalytic materials with enhanced performance. Moreover, these catalysts can be recovered and reused for at least nine times without loss of activity or can be easily regenerated when their activity has decreased. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Asymmetric Aldol Reaction of Ketones with Alkenyl Trichloroacetates Catalyzed by Dibutyltin Dimethoxide and BINAP,Silver(I) Complex: Construction of a Chiral Tertiary Carbon CenterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Akira Yanagisawa Abstract A novel aldol reaction of alkenyl trichloroacetates with ,-keto esters was realized by using dibutyltin dimethoxide as a catalyst, which was regenerated by the addition of methanol. The reaction was found to be remarkably accelerated by the addition of a catalytic amount of a bidentate phosphine,silver(I) complex. Use of the BINAP,silver triflate (AgOTf) complex as the chiral co-catalyst resulted in the formation of optically active aldol products possessing a chiral tertiary carbon with up to 93% ee. This catalytic method was further applied to the asymmetric reaction of diketene with methyl benzoylformate. [source] The Ion Tag Strategy as a Route to Highly Efficient Organocatalysts for the Direct Asymmetric Aldol ReactionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Marco Lombardo Abstract The installation of an imidazolium tag via acetate connection to the C-4 of cis -4-hydroxy- L -proline provides a highly efficient catalyst for the direct asymmetric aldol reaction, that works in a remarkably low catalyst loading (0.1,mol%) affording TONs up to 930 in the case of electron-poor aromatic aldehydes with ee up to >99%. [source] New Simple Hydrophobic Proline Derivatives as Highly Active and Stereoselective Catalysts for the Direct Asymmetric Aldol Reaction in Aqueous MediumADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2008Francesco Giacalone Abstract New 4-substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes. Reactions were carried out using water, this being the best reaction medium examined. Screening of these catalysts showed that compounds bearing the most hydrophobic acyl chains [4-phenylbutanoate and 4-(pyren-1-yl)butanoate] provided better results. The latter catalysts were successfully used in only 2 mol% at room temperature without additives to give aldol products in excellent stereoselectivities. These results demonstrate that derivatization of the proline moiety with the proper simple hydrophobic substituent in the 4-position can furnish highly active and stereoselective catalysts without the need of additional chiral backbones in the molecule. Finally, an explanation of the observed stereoselectivities in the presence of water is provided. [source] An Improved Protocol for the Direct Asymmetric Aldol Reaction in Ionic Liquids, Catalysed by Onium Ion-Tagged ProlinesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2007Marco Lombardo Abstract Two onium ion-tagged prolines, imidazolium bis(trifluoromethylsulfonyl)imide-substituted proline 6 and butyldimethylammonium bis(trifluoromethylsulfonyl)imide-substituted proline 7, were synthesised and their catalytic activity in the direct asymmetric aldol condensation was studied in ionic liquids. For the reaction of acetone with various aldehydes, using 5,% of the catalyst, the yields of the aldols varied between 50,85,% while the ee values were in the 80,85,% range. Other ketones were studied too, the yields obtained in those cases being in the 35,78,% range while the enantioselectivities varied between 75,94,%. [source] ChemInform Abstract: Construction of Contiguous Tetrasubstituted Chiral Carbon Stereocenters via Direct Catalytic Asymmetric Aldol Reaction of ,-Isothiocyanato Esters with Ketones.CHEMINFORM, Issue 16 2010Tatsuhiko Yoshino Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Merrifield Resin Supported Ionic Liquids/L-Proline as Efficient and Recyclable Catalyst Systems for Asymmetric Aldol Reaction.CHEMINFORM, Issue 14 2010Zuli Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Direct Catalytic Asymmetric Aldol Reaction of ,-Keto Esters with Formaldehyde Promoted by a Dinuclear Ni2 -Schiff Base Complex.CHEMINFORM, Issue 1 2010Shinsuke Mouri Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: The Ion Tag Strategy as a Route to Highly Efficient Organocatalysts for the Direct Asymmetric Aldol Reaction.CHEMINFORM, Issue 23 2009Marco Lombardo Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Protonated Arginine and Lysine as Catalysts for the Direct Asymmetric Aldol Reaction in Ionic Liquids.CHEMINFORM, Issue 10 2009Marco Lombardo Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Organocatalytic Asymmetric Aldol Reaction of Ketones with Isatins: Straightforward Stereoselective Synthesis of 3-Alkyl-3-hydroxyindolin-2-ones.CHEMINFORM, Issue 5 2008Jia-Rong Chen Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Dibutyltin Dimethoxide and BINAP×Silver(I) Complex-Catalyzed Asymmetric Aldol Reaction of Alkenyl Trichloroacetates with Aldehydes.CHEMINFORM, Issue 19 2007Akira Yanagisawa Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Sterically and Electronically Tunable and Bifunctional Organocatalysts: Design and Application in Asymmetric Aldol Reaction of Cyclic Ketones with Aldehydes.CHEMINFORM, Issue 6 2007Jia-Rong Chen Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Recycling Chiral Organocatalyst (4S)-Phenoxy-(S)-proline for Direct Asymmetric Aldol Reaction in Ionic Liquid (bmim)PF6.CHEMINFORM, Issue 39 2005Yan-Hua Liu Abstract For Abstract see ChemInform Abstract in Full Text. [source] One-Pot Synthesis of ,-Diazo-,-hydroxyesters under Phase-Transfer Catalysis and Application to the Catalytic Asymmetric Aldol Reaction.CHEMINFORM, Issue 19 2004Shigeru Arai Abstract For Abstract see ChemInform Abstract in Full Text. [source] Discovery of New Peptide-Based Catalysts for the Direct Asymmetric Aldol Reaction.CHEMINFORM, Issue 43 2003Jacob Kofoed Abstract For Abstract see ChemInform Abstract in Full Text. [source] Direct Catalytic Asymmetric Aldol Reaction of Hydroxyketones: Asymmetric Zn Catalysis with a Et2Zn/Linked-BINOL Complex.CHEMINFORM, Issue 26 2003Naoya Kumagai Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: An Efficient Asymmetric Aldol Reaction of Chan,s Diene Promoted by Chiral Ti(IV),BINOL Complex.CHEMINFORM, Issue 37 2001Annunziata Soriente Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Hydrophobically Directed Aldol Reactions: Polystyrene-Supported L -Proline as a Recyclable Catalyst for Direct Asymmetric Aldol Reactions in the Presence of Water,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2007Michelangelo Gruttadauria Abstract A simple synthetic methodology for the preparation of a polystyrene-supported L -proline material is reported, and this material has been used as catalyst in direct asymmetric aldol reactions between several ketones and arylaldehydes to furnish aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water or methanol, at lower levels of conversion in the latter case. This solvent effect, coupled with the observed high stereoselectivities, has been explained in terms of the formation of a hydrophobic core in the inner surface of the resin, whereas the hydrophilic proline moiety lies at the resin/water interface. Such a microenvironment both promotes the aldol reaction and increases the stereoselectivity. Recycling investigations have shown that this material can be reused, without loss in levels of conversion and stereoselectivity, for at least five cycles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [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] Highly Efficient Threonine-Derived Organocatalysts for Direct Asymmetric Aldol Reactions in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2007Xiaoyu Wu Abstract The introduction of siloxy groups at the hydroxy function of natural threonine resulted in efficient hydrophobic organocatalysts, which could efficiently catalyze the direct aldol reactions of both cyclic and acyclic ketones with aromatic aldehydes in water with excellent enantiomeric excess. [source] Catalytic Asymmetric Aldol Reactions of Enolizable Carbon Pronucleophiles with Formaldehyde and Ethyl GlyoxylateADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2007Isao Fukuchi Abstract We herein describe novel catalytic asymmetric aldol reactions of acidic carbon pronucleophiles including ,-keto esters and specific ketones with reactive electrophiles such as formaldehyde and ethyl glyoxylate. In the presence of a catalytic amount of chiral Pd(II)-BINAP complexes, the hydroxymethylation of ,-keto esters with paraformaldehyde or formalin was examined, and the corresponding adducts were obtained in good yields with good to high enantioselectivity (ca. 86,% ee). In some cases, the similar Pt(II) complex also worked well to give the products with better enantioselectivity. Furthermore, these complexes were found to promote the aldol reactions of less acidic ketones, and ethyl glyoxylate underwent reaction with 3-coumaranone and ,-tetralone, affording the aldol products with a significant level of enantioselectivity of up to 83,% ee. [source] ChemInform Abstract: Organocatalytic Asymmetric Aldol Reactions Mediated by a Cysteine-Derived Prolinamide.CHEMINFORM, Issue 48 2008Ricardo S. Schwab Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Direct Catalytic Asymmetric Aldol Reactions of Aldehydes.CHEMINFORM, Issue 28 2002Anders Boegevig Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Direct Catalytic Asymmetric Aldol Reactions Promoted by Novel Heterobimetallic Catalysts Possessing Strong Broensted Base: A New Strategy for the Development of Lewis Acid,Broensted Base Bifunctional Catalysts.CHEMINFORM, Issue 32 2001Naoki Yoshikawa Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Desymmetrisation of a Centrosymmetric Molecule by Carbon,Carbon Bond Formation: Asymmetric Aldol Reactions of a Centrosymmetric DialdehydeCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2007Karen Dodd Abstract The desymmetrisation of centrosymmetric molecules by enantioselective carbon,carbon bond formation has been reported for the first time. A bimetallic zinc catalyst developed by Trost was exploited in the desymmetrisation of a centrosymmetric dialdehyde. The approach was successful with a range of ketone nucleophiles and was uniformly highly diastereoselective (>98:<2). The yield and the enantioselectivity of the reaction varied as a function of the ketone used, and the desymmetrised products were obtained in up to 74,% yield and 97,%,ee (ee=enantiomeric excess). The desymmetrisation of centrosymmetric molecules by enantioselective carbon,carbon bond formation is an efficient and convergent synthetic approach which is likely to find wide application in synthesis, particularly in the total synthesis of natural products with embedded centrosymmetric fragments. [source] Asymmetric aldol reactions catalyzed by efficient and recyclable silica-supported proline-based peptidesCHIRALITY, Issue 4 2009Jincan Yan Abstract A series of silica-supported proline-based peptides were synthesized and applied as catalysts for direct asymmetric intermolecular aldol reactions. Among these, a peptide with two L -proline units was found to be the most efficient one for the asymmetric aldol reactions between acetone and aromatic aldehydes. The reactions generated the corresponding products with satisfactory isolated yields (up to 97%) and enantiomeric excesses (up to 96%) in the presence of this catalyst (5 mol %). Furthermore, the silica-supported organocatalyst could be recovered and recycled by a simple filtration of the reaction solution and used for five consecutive trials without loss of its reactivity. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source] Synthesis, asymmetric aldol reactions, and x-ray crystallography of some oxadiazinanone derivativesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2008Shawn R. Hitchcock A series of N4 -substituted oxadiazinanones have been synthesized from (1R,2S)-norephedrine by a process of either reductive alkylation or arylation, N -nitrosation, reduction and cyclization. These derivatives (R = -CH2Ph, -CH2C(CH3)3, - cyclo -C6H11, -C6H5) have been acylated with propanoyl chloride and employed in the asymmetric Aldol reaction. The observed diastereoselectivities for the formation of the "non-Evans" syn-adduct ranged from 88:12 to 99:1. The hydrolysis of the Aldol adducts varied with the nature of the nitrogen substituent. [source] Advances towards Highly Active and Stereoselective Simple and Cheap Proline-Based Organocatalysts,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 29 2010Francesco Giacalone Abstract Ten 4-acyloxy- L -prolines were screened as catalysts at loadings of 2,0.1 mol-% for the direct asymmetric aldol reaction in water by using variable amounts of water. Among them, a new catalyst, the L -proline carrying a trans -4-(2,2-diphenylacetoxy) group, and a catalyst previously synthesized by us, the L -proline carrying a trans -4-(4-phenylbutanoyloxy) group, were found to be excellent catalysts for the aldol reaction between cyclohexanone or cyclopentanone and substituted benzaldehydes when employed in only 1 and 0.5 mol-%,respectively, at room temperature without additives. For such catalysts, high turnover numbers were obtained, which are among the highest values obtained for enamine organocatalysis. Finally, these catalysts can be synthesized by direct O -acylation from inexpensive molecules and successfully used in scaled-up reactions. [source] Enhanced Activity and Stereoselectivity of Polystyrene-Supported Proline-Based Organic Catalysts for Direct Asymmetric Aldol Reaction in WaterEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2009Michelangelo Gruttadauria Abstract Several polystyrene-supported proline dipeptides and a prolinamide derivative were prepared by thiol,ene coupling. These materials were used as catalysts for the direct asymmetric aldol reaction in water, and results compared with unsupported catalysts in water. Such an approach gave more active or stereoselective catalysts compared to the unsupported compounds, showing that our immobilization procedure may be useful to develop catalytic materials with enhanced performance. Moreover, these catalysts can be recovered and reused for at least nine times without loss of activity or can be easily regenerated when their activity has decreased. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] | ||||||||||