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Aldol Condensation (aldol + condensation)
Terms modified by Aldol Condensation Selected AbstractsMorpholinium Trifluoroacetate-Catalyzed Aldol Condensation of Acetone with both Aromatic and Aliphatic AldehydesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010Kristina Zumbansen Abstract We report a highly efficient, general and practical method for the aldol condensation of acetone with aromatic and aliphatic aldehydes, using morpholinium trifluoroacetate as a catalyst. [source] ChemInform Abstract: Microwave-Assisted Aldol Condensation of Benzil with Ketones.CHEMINFORM, Issue 36 2009Katayoun Marjani 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: Enantioselective Synthesis of the Tetrahydro-6H-benzo[c]chromenes via Domino Michael,Aldol Condensation: Control of Five Stereocenters in a Quadruple-Cascade Organocatalytic Multi-Component Reaction.CHEMINFORM, Issue 21 2009Prakash Kotame 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: Synthesis of ,-Hydroxybutenolides Applying Crossed Aldol Condensation in the Presence of a Bulky Lewis Acid and Their Antitumor Activity.CHEMINFORM, Issue 6 2008Yumiko Yamano 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] Bimorpholine-Mediated Enantioselective Intramolecular and Intermolecular Aldol Condensation.CHEMINFORM, Issue 49 2007Tonis Kanger 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] Enantioselective Aldol Condensation of O-Silyldienolates Derived from Alkyl-Substituted 2,2-Dimethyl-[1,3]-dioxin-4-ones.CHEMINFORM, Issue 9 2005Margherita De Rosa Abstract For Abstract see ChemInform Abstract in Full Text. [source] A Convenient Catalytic Procedure for the Highly Enantioselective Aldol Condensation of O-Silyldienolates.CHEMINFORM, Issue 52 2003Margherita De Rosa Abstract For Abstract see ChemInform Abstract in Full Text. [source] Methyl 3,3-Difluoro-2-trimethylsilyoxyacrylate: Preparation and Mukaiyama-Type Aldol Condensation as a Novel Route to ,,,-Difluoro-,-keto Ester Derivatives.CHEMINFORM, Issue 48 2002Biao Jiang Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Stereochemistry of Aldol Condensation of N,N-Dialkyl Amides with Aromatic Imines.CHEMINFORM, Issue 9 2001-Amino Acid Dialkylamides., Highly Diastereoselective Synthesis of 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] How Many Elementary Processes Are Involved in Base- and Acid-Promoted Aldol Condensations?EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 36 2007Shinichi Yamabe Abstract The title reactions were investigated by density functional theory calculations. MeRC=O + OH, + (H2O)8 (R = H and Me) and MeCH=O + H3O+ + (H2O)8 systems were adopted to trace the elementary processes. Eight water molecules were included to assure proton shifts through hydrogen bonds. The OH, -containing reactions were confirmed to have three elementary processes. Whereas the rate-determining step of the reaction of acetaldehyde is C,H bond scission, that of acetone is C,C bond formation. The H3O+ -containing reactions have two elementary processes. The reactivity difference between OH, - and H3O+ -promoted reactions was discussed in terms of their mobility and hydration strength. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Aldol Condensations of Aldehydes and Ketones Catalyzed by Rare Earth(III) Perfluorooctane Sulfonates in Fluorous Solvents.CHEMINFORM, Issue 15 2006Wen-Bin Yi 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] Tandem Radical Addition,Aldol Condensations: Evidence for the Formation of Zinc Enolates in Diethylzinc Mediated Radical Additions to N-Enoyloxazolidinones.CHEMINFORM, Issue 11 2003S. Bazin Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: A Sequence of Aldol Condensations and a Michael Addition Giving a Cyclohexenone Ring System.CHEMINFORM, Issue 26 2001Ulrich Kuhl 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] Alkaline hydrolysis of cinnamaldehyde to benzaldehyde in the presence of ,-cyclodextrinAICHE JOURNAL, Issue 2 2010Hongyan Chen Abstract A facile, novel, and cost-effective alkaline hydrolysis process of cinnamaldehyde to benzaldehyde under rather mild conditions has been investigated systematically in the presence of ,-cyclodextrin (,-CD), with water as the only solvent. ,-CD could form inclusion complex with cinnamaldehyde in water, with molar ratio of 1:1, so as to promote the reaction selectivity. The complex has been investigated experimentally and with computational methods. 1H-NMR, ROESY, UV,Vis, and FTIR have been utilized to analyze the inclusion complex. It shows that the equilibrium constant for inclusion (Ka) is 363 M,1, and the standard Gibbs function for the reaction, ,,G (298 K), is ,14.6 kJ mol,1. In addition, the structures of the proposed inclusion compounds were optimized with hybrid ONIOM theory. Benzaldehyde could be obtained at an yield of 42% under optimum conditions [50°C, 18 h, 2% NaOH (w/v), cinnamaldehyde:,-CD (molar ratio) = 1:1]. To explain the experimental data, NMR, FTIR, and elemental analysis results were used to determine the main reaction by-product 1-naphthalenemethanol. A feasible reaction mechanism including the retro-Aldol condensation of cinnamaldehyde and the Aldol condensation of acetaldehyde and cinnamaldehyde in basic aqueous ,-CD solution has been proposed. The calculated activation energy for the reaction was 45.27 kJ mol,1 by initial concentrations method. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Synthesis of New Camptothecin Analogues with the E-Lactone Ring Replaced by ,,,-CyclohexenoneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006Valeriy A. Bacherikov Abstract The total synthesis of racemic camptothecin analogues 12a and 12b, in which the E-lactone ring has been replaced by an ,,,-cyclohexenone ring and the ethyl and hydroxy substituents have been retained, was achieved by first preparing the ABCD fragments 31a and 31b, which were then converted into the tetracyclic triol 36a and 36b by osmium-mediated dihydroxylation. Compounds 36a and 36b were oxidized in one-pot reactions, followed by intramolecular aldol condensation to furnish the desired pentacyclic 12a and 12b, which retained topoisomerase I inhibitory activity and exhibited cytotoxicity to tumor cell growth in culture.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The Development of a Convergent and Efficient Enantioselective Synthesis of the Bengamides via a Common Polyol IntermediateHELVETICA CHIMICA ACTA, Issue 12 2002Robert An efficient, general synthetic route to the bengamide family of antitumor agents from a common polyol thioester is described. Consecutive aldol condensations afford the protected polyol thioester side chain suitable for coupling to the bengamides. A novel chiral-phase-transfer-catalyzed enantioselective alkylation affords the properly functionalized caprolactams required for the synthesis of more-complex members of the bengamide family. Use of the methyl 2-naphthyl ether protecting group, compatible with the boron Lewis acids required for enantioselective aldol condensation, allows direct access to all the bengamides. [source] The Efficient and Enantiospecific Total Synthesis of Cyclopenta[b]phenanthrenes Structurally-Related to NeurosteroidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Mingxing Qian Abstract We report an efficient synthesis of cyclopenta[b]phenanthrenes functionalized at C-3 and C-8 from an optically pure Hajos,Parrish ketone. The key step is a neutral alumina-catalyzed Michael addition of a Hajos,Parrish ketone derivative (4) to 1,7-octadien-3-one (2) in 98% yield. This Michael addition product went through Krapcho decarbomethoxylation, aldol condensation, lithium liquid ammonia reduction, Wacker oxidation and acid-catalyzed cyclization to form cyclopenta[b]phenanthrene (1a) in 37% overall yield for the 7 steps. [source] Morpholinium Trifluoroacetate-Catalyzed Aldol Condensation of Acetone with both Aromatic and Aliphatic AldehydesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010Kristina Zumbansen Abstract We report a highly efficient, general and practical method for the aldol condensation of acetone with aromatic and aliphatic aldehydes, using morpholinium trifluoroacetate as a catalyst. [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] 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] Hydrothermal conversion of carbohydrate biomass to lactic acidAICHE JOURNAL, Issue 10 2010Xiuyi Yan Abstract We investigated the hydrothermal conversion of the carbohydrates including glucose, cellulose, and starch to lactic acid using NaOH and Ca(OH)2 as alkaline catalysts. Both catalysts significantly promoted the lactic acid formation. The highest yield of lactic acid from glucose was 27% with 2.5 M NaOH and 20% with 0.32 M Ca(OH)2 at 300°C for 60 s. The lactic acid yields from cellulose and starch were comparable with the yield from glucose with 0.32 M Ca(OH)2 at 300°C, but the reaction time in the case of cellulose was 90 s. The mechanism of lactic acid formation from glucose was discussed by identifying the intermediate products. Lactic acid may be formed via the formation of aldoses of two to four carbons including aldose of three carbons, which are all formed by reverse aldol condensation and double bond rule of hexose. This implies that carbon,carbon cleavage occurs at not only C3C4 but also at C2C3. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Stereoselective synthesis of radiolabelled avermectinsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 1 2005Bruce P. McKillican Abstract The natural products avemectin B1a1a and B1b1b were each site-specifically 14C labelled at carbon 23 in a convergent synthesis for metabolism, residue, and environmental studies. The 12-step radiosynthesis involved a stereoselective aldol condensation and later a coupling to a protected avermectin degradate 2 in a one-pot Wittig condensation/spiroketalization to reconstitute the dioxaspirane configuration found in the natural products. Copyright © 2004 John Wiley & Sons, Ltd. [source] Characterization of ring-opening polymerization of genipin and pH-dependent cross-linking reactions between chitosan and genipinJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2005Fwu-Long Mi Abstract In this study, a novel chitosan-based polymeric network was synthesized by crosslinking with a naturally occurring crosslinking agent,genipin. The results showed that the crosslinking reactions were pH-dependent. Under basic conditions, genipin underwent a ring-opening polymerization prior to crosslinking with chitosan. The crosslink bridges consisted of polymerized genipin macromers or oligomers (7 , 88 monomer units). This ring-opening polymerization of genipin was initiated by extracting proton from the hydroxyl groups at C-1 of deoxyloganin aglycone, followed by opening the dihydropyran ring to conduct an aldol condensation. At neutral and acidic conditions, genipin reacted with primary amino groups on chitosan to form heterocyclic amines. The heterocyclic amines were further associated to form crosslinked networks with short chains of dimmer, trimer, and tetramer bridges. An accompanied reaction of nucleophilic substitution of the ester group on genipin by the primary amine group on chitosan would occur in the presence of an acid catalysis. The extent in which chitosan gels crosslinked with genipin was significantly dependent on the crosslinking pH values: 39.9 ± 3.8% at pH 5.0, 96.0 ± 1.9% at pH 7.4, 45.4 ± 1.8% at pH 9.0, and 1.4 ± 1.0% at pH 13.6 (n = 5, p < 0.05). Owing to the different crosslinking extents and different chain lengths of crosslink bridges, the genipin-crosslinked chitosan gels showed significant difference in their swelling capability and their resistance against enzymatic hydrolysis, depending on the pH conditions for crosslinking. These results indicated a direct relationship between the mode of crosslinking reaction, and the swelling and enzymatic hydrolysis properties of the genipin-crosslinked chitosan gels. The ring-opening polymerization of genipin and the pH-dependent crosslinking reactions may provide a novel way for the preparation and exploitation of chitosan-based gels for biomedical applications. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1985,2000, 2005 [source] Green chemistry synthesis: 2-amino-3-[(E)-(2-pyridyl)methylideneamino]but-2-enedinitrile monohydrate and 5-cyano-2-(2-pyridyl)-1-(2-pyridylmethyl)-1H -imidazole-4-carboxamideACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Muhammad Altaf The title compounds, C10H9N5O·H2O (L1·H2O) and C16H12N6O (L2), were synthesized by solvent-free aldol condensation at room temperature. L1, prepared by grinding picolinaldehyde with 2,3-diamino-3-isocyanoacrylonitrile in a 1:1 molar ratio, crystallized as a monohydrate. L2 was prepared by grinding picolinaldehyde with 2,3-diamino-3-isocyanoacrylonitrile in a 2:1 molar ratio. By varying the conditions of crystallization it was possible to obtain two polymorphs, viz. L2-I and L2-II; both crystallized in the monoclinic space group P21/c. They differ in the orientation of one pyridine ring with respect to the plane of the imidazole ring. In L2-I, this ring is oriented towards and above the imidazole ring, while in L2-II it is rotated away from and below the imidazole ring. In all three molecules, there is a short intramolecular N,H...N contact inherent to the planarity of the systems. In L1·H2O, this involves an amino H atom and the C=N N atom, while in L2 it involves an amino H atom and an imidazole N atom. In the crystal structure of L1·H2O, there are N,H...O and O,H...O intermolecular hydrogen bonds which link the molecules to form two-dimensional networks which stack along [001]. These networks are further linked via intermolecular N,H...N(cyano) hydrogen bonds to form an extended three-dimensional network. In the crystal structure of L2-I, symmetry-related molecules are linked via N,H...N hydrogen bonds, leading to the formation of dimers centred about inversion centres. These dimers are further linked via N,H...O hydrogen bonds involving the amide group, also centred about inversion centres, to form a one-dimensional arrangement propagating in [100]. In the crystal structure of L2-II, the presence of intermolecular N,H...O hydrogen bonds involving the amide group results in the formation of dimers centred about inversion centres. These are linked via N,H...N hydrogen bonds involving the second amide H atom and the cyano N atom, to form two-dimensional networks in the bc plane. In L2-I and L2-II, C,H..., and ,,, interactions are also present. [source] Structure of aldolase from Thermus thermophilus HB8 showing the contribution of oligomeric state to thermostabilityACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2004Neratur K. Lokanath 2-Deoxyribose-5-phosphate aldolase catalyzes a reversible aldol condensation of two aldehydes via formation of a covalent Schiff-base intermediate at the active lysine residue. The crystal structure of 2-deoxyribose-5-phosphate aldolase from Thermus thermophilus HB8 has been determined with and without the substrate at atomic resolution. This enzyme, which has a unique homotetramer structure, has been compared with the previously reported crystal structures of two orthologues from Escherichia coli and Aeropyrum pernix. In contrast to the similar ,/,-barrel fold of the monomers, substantial quaternary structural differences are observed between these three enzymes. Further comparison of the subunit,subunit interface areas of these aldolases showed a clear positive correlation between the interface area and the living temperature of the source organism. From these results, it is concluded that the oligomeric state of 2-deoxyribose-5-phosphate aldolase is important for the thermostability and not for the catalytic function. [source] The Development of a Convergent and Efficient Enantioselective Synthesis of the Bengamides via a Common Polyol IntermediateHELVETICA CHIMICA ACTA, Issue 12 2002Robert An efficient, general synthetic route to the bengamide family of antitumor agents from a common polyol thioester is described. Consecutive aldol condensations afford the protected polyol thioester side chain suitable for coupling to the bengamides. A novel chiral-phase-transfer-catalyzed enantioselective alkylation affords the properly functionalized caprolactams required for the synthesis of more-complex members of the bengamide family. Use of the methyl 2-naphthyl ether protecting group, compatible with the boron Lewis acids required for enantioselective aldol condensation, allows direct access to all the bengamides. [source] | |||||||||||||||||||||||||