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Direct Aldol Reactions (direct + aldol_reaction)
Selected AbstractsA 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] Dendritic Amplification of Stereoselectivity of a Prolinamide-Catalyzed Direct Aldol ReactionISRAEL JOURNAL OF CHEMISTRY, Issue 1 2009Kazuhiko Mitsui Isomeric "compact" and "expanded" dendrimers functionalized with L -prolinamide catalytic units at the periphery were compared as catalysts to monomer controls in the organocatalytic direct aldol condensation. A positive dendritic effect that amplifies the stereoselectivity of the direct aldol condensation was observed for dendrimers 3 and 4, compared with lower molecular weight catalysts L -prolinani-lide 1 and G1 dendron 2. The difference in the compactness between 3 and 4 appears to have less impact on the stereoselectivity than the preorganized multivalency of the dendritic catalysts. [source] ChemInform Abstract: Highly Enantioselective Synthesis of Tertiary Alcohols: C2 -Symmetric N,N,-Dioxide-Sc(III) Complex Promoted Direct Aldol Reaction of ,-Ketoesters and Diazoacetate Esters.CHEMINFORM, Issue 16 2010Fei 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] Highly Enantioselective Organocatalytic Direct Aldol Reaction in an Aqueous Medium.CHEMINFORM, Issue 43 2007Vishnu Maya 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] trans-4-Hydroxy-L-proline Hydrazide,Trifluoroacetic Acid as Highly Stereoselective Organocatalyst for the Asymmetric Direct Aldol Reaction of Cyclohexanone.CHEMINFORM, Issue 4 2007Chuanling Cheng 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] Asymmetric Direct Aldol Reaction Assisted by Water and a Proline-Derived Tetrazole Catalyst.CHEMINFORM, Issue 31 2004Hiromi Torii Abstract For Abstract see ChemInform Abstract in Full Text. [source] Effect of Long Chain Fatty Acids on Organocatalytic Aqueous Direct Aldol ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Nobuyuki Mase Abstract In an organocatalyzed, aqueous direct aldol reaction, the addition of a long chain fatty acid (1,mol%) such as stearic acid or erucic acid improved the aldol product yield and the enantioselectivity with low catalyst loading (1,mol%). The small particle size of the emulsion (less than 1,,m) was a key to the enhanced reactivity as shown by dynamic light scattering (DLS) analyses. [source] ChemInform Abstract: Inorganic Ammonium Salts as Catalysts for Direct Aldol Reactions in the Presence of Water.CHEMINFORM, Issue 15 2010Pawel Dziedzic 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: Effect of Long Chain Fatty Acids on Organocatalytic Aqueous Direct Aldol Reactions.CHEMINFORM, Issue 13 2010Nobuyuki Mase 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: (S)-Pyrrolidine Sulfonamide Catalyzed Asymmetric Direct Aldol Reactions of Aryl Methyl Ketones with Aryl Aldehydes.CHEMINFORM, Issue 33 2008Shilei Zhang 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] Asymmetric Organocatalytic Direct Aldol Reactions of Cyclohexanone with Aldehydes in Brine.CHEMINFORM, Issue 43 2007Wen-Ping Huang 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] Highly Diastereo- and Enantioselective Direct Aldol Reactions of Cycloketones with Aldehydes Catalyzed by a trans-4-tert-Butyldimethylsiloxy-L-proline Amide.CHEMINFORM, Issue 27 2007Long He 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] Organocatalyzed Highly Enantioselective Direct Aldol Reactions of Aldehydes with Hydroxyacetone and Fluoroacetone in Aqueous Media: The Use of Water To Control RegioselectivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Xiao-Hua Chen Abstract An organocatalyst prepared from (2R,3R)-diethyl 2-amino-3-hydroxysuccinate and L -proline exhibited high regio- and enantioselectivities for the direct aldol reactions of hydroxyacetone and fluoroacetone with aldehydes in aqueous media. It was found that water could be used to control the regioselectivity. The presence of 20,30 mol,% of the catalyst afforded the direct aldol reactions of a wide range of aldehydes with hydroxyacetone to give the otherwise disfavored products with excellent enantioselectivities, ranging from 91 to 99,%,ee, and high regioselectivities. Aldolizations of fluoroacetone with aldehydes mediated by 30 mol,% of the organocatalyst in aqueous media preferentially occurred at the methyl group, yielding products with high enantioselectivities (up to 91,%,ee); however, these additions took place dominantly at the fluoromethyl group in THF. Optically active 3,5-disubstituted tetrahydrofurans and (2S,4R)-dihydroxy-4-biphenylbutyric acid were prepared by starting from the aldol reaction of hydroxyacetone. Theoretical studies on the role of water in controlling the regioselectivity revealed that the hydrogen bonds formed between the amide oxygen of proline amide, the hydroxy of hydroxyacetone, and water are responsible for the regioselectivity by microsolvation with explicit one water molecule as a hydrogen-bond donor and/or an acceptor. [source] Stereoselective Aldol Reactions Catalyzed by Acyclic Amino Acids in Aqueous MicellesHELVETICA CHIMICA ACTA, Issue 1 2007Dong-Sheng Deng Abstract The catalytic properties of all proteinogenic, acyclic amino acids for direct aldol reaction in H2O, assisted by various surfactants, were investigated. The basic and neutral amino acids were shown to be efficient catalysts, giving rise to good-to-excellent yields of adducts (up to 95%), with moderate-to-good diastereoselectivities (up to 86%), L -arginine being the most-effective catalyst. The syn/anti diastereoisomer ratio could be readily tuned by proper choice of the amino acid used. Also, the range of substrates that underwent the reaction was extended to less-reactive aldehydes carrying electron-donating Br substituents. [source] Effect of Long Chain Fatty Acids on Organocatalytic Aqueous Direct Aldol ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Nobuyuki Mase Abstract In an organocatalyzed, aqueous direct aldol reaction, the addition of a long chain fatty acid (1,mol%) such as stearic acid or erucic acid improved the aldol product yield and the enantioselectivity with low catalyst loading (1,mol%). The small particle size of the emulsion (less than 1,,m) was a key to the enhanced reactivity as shown by dynamic light scattering (DLS) analyses. [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] The First Catalytic Enantioselective Aldol-Type Reaction of Ethyl Diazoacetate to KetonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Fides Benfatti Abstract The aldol-type addition to ketones still represents a great challenge in asymmetric catalysis. Recently, the direct aldol reaction between the commercially available ethyl diazoacetate and aldehydes has attracted increasing attention. Ethyl diazoacetate is economical and allows further transformation of the aldol adduct obtained. We present a solution for the arduous, and not previously described, addition of diazoacetate to ketones. Our procedure employs commercially available norephedrine-derived ligands and dialkylzinc reagents [R2Zn: (diethylzinc, Et2Zn; dimethylzinc, Me2Zn)] as starting materials, therefore the active catalyst is prepared with a very straightforward methodology. Remarkably, the reaction gives good enantiomeric excesses with ,-halo ketones, a class of compounds that has not been commonly used in enolate addition. [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] Total Synthesis of the Cyclodepsipeptide Apratoxin A and Its Analogues and Assessment of Their Biological ActivitiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2006Dawei Ma Prof. Dr. Abstract A novel total synthesis of apratoxin A is described, with key steps including the assembly of its ketide segment through a D -proline-catalyzed direct aldol reaction and Oppolzer's anti aldol reaction and the preparation of its thiazoline unit in a biomimetic synthesis. An oxazoline analogue of apratoxin A has also been elaborated by a similar approach. This compound has a potency against HeLa cell proliferation only slightly lower than that of apratoxin A, whilst a C(40)-demethylated oxazoline analogue of apratoxin A displays a much lower cytotoxicity and the C(37)-epimer and C(37) demethylation product of this new analogue are inactive. These results suggest that the two methyl groups at C(37) and C(40) and the stereochemistry at C(37) are essential for the potent cellular activity of the oxazoline analogue of apratoxin A. Further biological analysis revealed that both synthetic apratoxin A and its oxazoline analogue inhibited cell proliferation by causing cell cycle arrest in the G1 phase. [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] Organocatalyzed Highly Enantioselective Direct Aldol Reactions of Aldehydes with Hydroxyacetone and Fluoroacetone in Aqueous Media: The Use of Water To Control RegioselectivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Xiao-Hua Chen Abstract An organocatalyst prepared from (2R,3R)-diethyl 2-amino-3-hydroxysuccinate and L -proline exhibited high regio- and enantioselectivities for the direct aldol reactions of hydroxyacetone and fluoroacetone with aldehydes in aqueous media. It was found that water could be used to control the regioselectivity. The presence of 20,30 mol,% of the catalyst afforded the direct aldol reactions of a wide range of aldehydes with hydroxyacetone to give the otherwise disfavored products with excellent enantioselectivities, ranging from 91 to 99,%,ee, and high regioselectivities. Aldolizations of fluoroacetone with aldehydes mediated by 30 mol,% of the organocatalyst in aqueous media preferentially occurred at the methyl group, yielding products with high enantioselectivities (up to 91,%,ee); however, these additions took place dominantly at the fluoromethyl group in THF. Optically active 3,5-disubstituted tetrahydrofurans and (2S,4R)-dihydroxy-4-biphenylbutyric acid were prepared by starting from the aldol reaction of hydroxyacetone. Theoretical studies on the role of water in controlling the regioselectivity revealed that the hydrogen bonds formed between the amide oxygen of proline amide, the hydroxy of hydroxyacetone, and water are responsible for the regioselectivity by microsolvation with explicit one water molecule as a hydrogen-bond donor and/or an acceptor. [source] | ||||||||||||||||||||||