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Direct Asymmetric Aldol Reaction (direct + 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] 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: 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] 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] 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] 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] 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] Water versus Solvent-Free Conditions for the Enantioselective Inter- and Intramolecular Aldol Reaction Employing L -Prolinamides and L -Prolinethioamides as OrganocatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Diana Alma Abstract Organocatalysts 1, derived from L -proline and (1S,2R)- cis -1-aminoindan-2-ol or (R)-1-aminoindane, are evaluated as promoters in the direct asymmetric aldol reaction between ketones and aromatic aldehydes in the presence of water and under solvent-free reaction conditions. L -Prolinethioamides 1c and 1d exhibited higher enantioselectivity than the corresponding prolinamides 1a and 1b in the model aldol reaction between cyclohexanone and 4-nitrobenzaldehyde in the presence of 4-nitrobenzoic acid as cocatalyst. In particular, L -prolinethioamide 1d (5,mol%), derived from L -proline and (R)-1-aminoindane, is shown as the most efficient organocatalyst studied promoting the direct aldol reaction of cycloalkyl, alkyl, and ,-functionalized ketones with aromatic aldehydes in the presence of water and under solvent-free reaction conditions employing only 2 equivalents of nucleophile. Generally, anti -aldol products are obtained in high yields and excellent diastereo- and enantioselectivities (up to >98/2 anti/syn, up to 98% ee). Solvent-free conditions give slightly higher dr and ee than using water as solvent. In addition, organocatalyst 1d can be easily recovered by extractive work-up and reused. Prolinethioamide 1d (5 mol%) in combination with 4-NO2C6H4CO2H (5 mol%) is also a very effective organocatalytic system for the asymmetric solvent-free intramolecular Hajos,Parrish,Eder,Sauer,Wiechert reaction with comparable or higher levels of enantioselectivity (up to 88% ee) to other reported catalysts in organic solvents. [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] Aldol reaction catalyzed by a hydrophilic catalyst in aqueous micelle as an enzyme mimic systemCHIRALITY, Issue 5 2009Hefeng Zhang Abstract Chitosan-supported L -proline complex was synthesized and applied as a catalyst for the direct asymmetric aldol reaction in various organic solvents and water as well. It was found that the novel synthesized catalyst was able to efficiently catalyze the aldol reaction in various media. The catalytic capacity and stereoselectivity of the catalyst were obviously improved with the introduction of aqueous micelle, possibly because the micelle functioned as a hydrophobic pocket, like the hydrophobic portion in enzymes. Moreover, the present synthetic catalyst showed performance similar to that of enzymes and could be used as a model of enzyme catalysis to help better understand the mystic mechanism of enzymes. Chirality, 2009. © 2008 Wiley-Liss, Inc. [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] A Novel Proline-Valinol Thioamide Small Organic Molecule for a Highly Enantioselective Direct Aldol ReactionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Bing Wang Abstract A new prolinethioamide compound 4, prepared from readily available natural amino acid L -proline and amino alcohol L -valinol, has been found to be an active catalyst for the direct aldol reaction of various aldehydes with acetone, cyclohexanone or cyclopentanone at 0,°C. Using only 2,mol% loading of this organocatalyst, the reaction could give high enantioselectivity with up to 96% enantiomeric excess for the reaction of 2-nitrobenzaldehyde with acetone. And as for the cyclohexanone, the excellent diastereoselectivity (anti/syn: 99/1) and enantioselectivity (99% ee) could be achieved when reacted with 3-nitrobenzaldehyde in water in the presence of this thioamide 4. This structurally simple catalyst is a highly efficient prolinethioamide derivative, and the terminal hydroxy group in this catalyst is a primary alcohol which is different from the previously reported prerequisite secondary or tertiary alcohol of prolinamides. Our results suggest a new strategy in the design of diversiform organic catalysts for direct asymmetric aldol reactions and related transformations. [source] | ||||||||||