Página 1 dos resultados de 45 itens digitais encontrados em 0.028 segundos

‣ Silica grafted polyethylenimine as heterogeneous catalyst for condensation reactions

Ribeiro, Sonia M.; Serra, Arménio. C.; Gonsalves, A. M. d’A. Rocha
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
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Primary amine groups were attached to a silica surface by using α,ω-diamines derivatives and (3-glycidyloxypropyl)-trimethoxysilane activation. The same activation was used to graft polyethylenimine, which also contains secondary and tertiary amine groups. These silica aminated structures were tested as heterogeneous catalysts in nitroaldol condensation with nitromethane, the derivative with the polyethylenimine moiety being the more active catalyst. This catalyst also showed efficiency in the Knoevenagel condensation of benzaldehydes with ethyl cyanoacetate under very mild reaction conditions and showed much the same efficiency when used in consecutive reaction runs. A reaction mechanism with participation of the several amine groups of the catalysts is discussed.

‣ As-synthesized TEA-BEA zeolite: Effect of Si/Al ratio on the Knoevenagel condensation

Chaves, Thiago F.; Pastore, Heloise O.; Hammer, Peter; Cardoso, Dilson
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 198-207
Português
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); The zeolite with BEA structure has been obtained using different Al amounts in the presence of tetraethylammonium as a structure directing agent. The effect of the Si/Al molar ratio on the crystal size, morphology, yield, chemical composition and catalytic properties was investigated. The materials have been characterized towards zeolitic properties by XRD, SEM, EDS, TGA, Si-29 MAS-NMR, XPS and TEM. The chemical composition of the crystals depends on the concentration of the initial reaction mixture and that a decrease in the Al content is associated with an increase in particle size. The characterization by TGA/DTA of as-synthesized zeolites with BEA structure showed that an increase of Si content resulted in the formation of [=Si-O-][TEA(+)] species, this was supported by Si-29 MAS-NMR. The XPS results also showed that the chemical composition of the surface differed from that of the bulk material, this was supported by TEM/EDS results. The results of catalytic activity tests indicated that a fraction of the [=Si-O-][TEA(+)]species was present on the external surfaces of the crystals, although the largest fraction appeared to be in the interior of the particles. As-synthesized BEA zeolite showed good catalytic activity and suggests that this material can be applied in other reactions involving basic sites. (C) 2014 Elsevier Inc. All rights reserved.

‣ Formylation, dicyanovinylation and tricyanovinylation on 5-alkoxy- and 5-amino-substituted-2,2´-bithiophenes

Raposo, M. Manuela M.; Kirsch, G.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2003 Português
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Several donor-acceptor-substituted bithiophenes were synthesized by functionalization of the corresponding 5-alkoxy- or 5-aminobithiophenes 1 by different methods: Vilsmeier formylation, metalation followed by reaction with DMF, direct tricyanovinylation reaction using TCNE or Knoevenagel condensation starting from the corresponding 5-formyl- derivatives of 1.; ICCTI/French Embassy (Technical and Scientific Cooperation Programme). Fundação para a Ciência e Tecnologia - POCTI/QUI/37816/2001, FMRH / BSAB / 134/99.

‣ Synthesis and characterization of novel efficient and thermally stable 2-aryl-5-dicyanovinylthiophenes and 5-aryl-5´-dicyanovinyl-2,2´-bithiophenes as potentially promising nonlinear optical (NLO) materials

Herbivo, Cyril; Comel, Alain; Kirsch, G.; Fonseca, A. Maurício C.; Belsley, M.; Raposo, M. Manuela M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
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Two series of dicyanovinyl-substituted compounds namely 2-aryl-5-dicyanovinyl-thiophenes 4 and 5-aryl-5´-dicyanovinyl-2,2´-bithiophenes 6 were synthesized through Knoevenagel condensation of the corresponding 2-aryl-5-formyl-thiophenes 3 and 5-aryl-5´-formyl-2,2´-bithiophene 5 precursors. On the other hand, precursors 3 were prepared through the Vilsmeier-Haack-Arnold reaction (VHA) starting from inexpensive and easily available precursors such as acetophenones. This method produced the title compounds in higher yields than the recently reported synthesis via Suzuki coupling of functionalized aryl boronic acids with 5-bromo-2-formyl-thiophene. Electrochemical studies and characterization of the optical (linear and nonlinear), and thermal properties for compounds 5-6 indicate that, good nonlinearity is complemented by exceptional thermal stability for chromophores 6, making them potential candidates for several optoelectronic applications such as solvatochromic probes and nonlinear optical materials.; Fundação para a Ciência e a Tecnologia (FCT) - PTDC/QUI/66251/2006, programa “Acções Integradas Luso-Francesas/CRUP-CPU

‣ Influence of basic properties of Mg,Al-mixed oxides on their catalytic activity in knoevenagel condensation between benzaldehyde and phenylsulfonylacetonitrile

Pérez,Caridad Noda; Monteiro,José Luiz Fontes; López Nieto,Jose Manoel; Henriques,Cristiane Assumpção
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 Português
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The catalytic performance of Mg,Al-mixed oxides (MO20, MO25 and MO33) derived from hydrotalcites was evaluated in the Knoevenagel reaction between benzaldehyde and phenylsulfonylacetonitrile at 373 and 383 K. The best results were obtained for the sample MO20 that presented the highest basic sites density and external area and the smallest crystallite sizes. The relative amount of basic sites with weak to intermediate strength also played an important role on catalytic performance. By increasing the catalyst content from 1 to 5 wt.% at 383 K, a complete conversion of the reactants is attained, producing α-phenylsulfonylcinnamonitrile with a selectivity of 100%.

‣ A green synthesis of α,β-unsaturated carbonyl compounds from glyceraldehyde acetonide

Veloso,Cláudia O.; Henriques,Cristiane A.; Dias,Ayres G.; Lima,Evanoel C. de; Souza,Bianca M.; Monteiro,José Luiz F.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2011 Português
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The catalytic behavior of Cs-exchanged and Cs-impregnated zeolites (X and Y) was studied using the Knoevenagel condensation between glyceraldehyde acetonide and ethyl acetoacetate in order to produce the corresponding α,β-unsaturated carbonyl compound that is an important intermediate for fine chemicals. The influence of reaction temperature, type of zeolite, and basicity of the sites on the catalytic behavior of the samples was evaluated. All zeolites were active for the studied reaction. The formation of the main condensation product was favored at lower reaction temperatures. Products of further condensations were also observed especially for samples that were only dried before catalytic test.

‣ Clean and atom-economic synthesis of alpha-phenylselenoacrylonitriles and alpha-phenylseleno- alpha,beta-unsaturated esters by knoevenagel reaction under solvent-free conditions

Perin,Gelson; Jacob,Raquel G.; Botteselle,Giancarlo V.; Kublik,Emerson L.; Lenardão,Eder J.; Cella,Rodrigo; Santos,Paulo César Silva dos
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2005 Português
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A simple, clean and efficient method has been developed for the synthesis of alpha-phenylselenoacrylonitriles and alpha-phenylseleno-alpha,beta-unsaturated esters by a one-pot reaction of aldehydes with phenylselenoacetonitrile or ethyl(phenylseleno)acetate respectively, in the presence of a solid supported catalyst (KF/Al2O3), without any solvent.

‣ Synthesis of α- and β-lapachone derivatives from hetero diels-alder trapping of alkyl and aryl o-quinone methides

Silva,Fernando de C. da; Ferreira,Sabrina B.; Kaiser,Carlos R.; Pinto,Angelo C.; Ferreira,Vitor F.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 Português
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Methylene and aryl o-quinone methides (o-QMs) generated by Knoevenagel condensation of 2-hydroxy-1,4-naphthoquinone with formaldehyde and arylaldehydes, undergo facile hetero Diels-Alder reaction with some substituted styrenes (as dienophiles) in aqueous ethanol media providing derivatives of α- and β-lapachone.

‣ Microwave-assisted synthesis under solvent-free conditions of (E)-2-(Benzo[d]thiazol-2-yl)-3-arylacrylonitriles

Trilleras,Jorge E.; Velasquez,Kelly J.; Pacheco,Dency J.; Quiroga,Jairo; Ortíz,Alejandro
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2011 Português
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A series of (E)-2-(benzo[d]thiazol-2-yl)-3-arylacrylonitriles was synthesized by microwave assisted Knoevenagel condensation under solvent-free conditions from the corresponding 2-(benzo[d]thiazol-2-yl)acetonitrile and aromatic aldehydes with electrondonating/electron-withdrawing groups. The reaction times were considerably short and the products obtained in moderate yields (50 to 75%) and good purity. The configuration of the acrylonitrile double bond could not be established by regular NMR methods. However, theoretical studies suggest that the E isomer is more stable than Z, which is in good agreement with some experimental evidences.

‣ Efficient synthesis of novel pyranoquinoline derivatives from simple acetanilide derivatives: experimental and theoretical study of their physicochemical properties using DFT calculations

Mirjafary,Zohreh; Saidian,Hamid; Sahandi,Morteza; Shojaei,Leila
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2014 Português
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A convenient reaction of 2-chloroquinoline-3-carbaldehyde derivatives and dimedone in the presence of KF-Al2O3 for the synthesis of useful pyranoquinolines is described. Reasonable yields (41-50%), easily available starting materials and less expensive efficient catalyst are the key features of the present method. A mechanism was proposed for the reaction course. Attribution of the chemical shifts was made with the help of the density functional theory (DFT) calculations. The computed nuclear magnetic resonance (NMR) chemical shifts are in good agreement with available experimental data. The nucleus-independent chemical shift (NICS) values were used as quantitative measures for the relative aromatic character in pyranoquinolines. The calculated NICS values obtained for the phenyl group of pyranoquinoline compounds are smaller than that of benzene.

‣ An efficient synthesis of novel pyrano[2,3-d]- and furopyrano[2,3-d]pyrimidines via indium-catalyzed multi-component domino reaction

Prajapati, Dipak; Gohain, Mukut
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
Publicado em 13/06/2006 Português
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Various novel pyrano [2,3-d]pyrimidines 5 and furopyrano [2,3-d]pyrimidines 7 were synthesized in 80–99% yields via a multicomponent domino Knoevenagel/hetero-Diels-Alder reaction of 1,3-dimethyl barbituric acid with an aromatic aldehyde and ethyl vinyl ether/2,3-dihydrofuran in presence of 1 mol% of indium(III) chloride. The reaction also proceeds in aqueous media without using any catalyst, but the yield is comparatively less (65–70%).

‣ Organocatalytic Highly Enantioselective Tandem Michael-Knoevenagel Reaction for the Synthesis of Substituted Thiochromanes

Dodda, Rajasekhar; Mandal, Tanmay; Zhao, Cong-Gui
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 17/03/2008 Português
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Enantioenriched tetrasubstituted thiochromanes have been synthesized using a tandem Michael addition-Knoevenagel reaction between 2-mercaptobenzaldehydes and benzylidenemalonates with a 9-epi-aminoquinine thiourea derivative as the catalyst. Steric and electron effects were found to affect profoundly the enantioselectivity and diastereoselectivity of the reaction.

‣ Hydroxyapatite supported caesium carbonate as a new recyclable solid base catalyst for the Knoevenagel condensation in water

Gupta, Monika; Gupta, Rajive; Anand, Medha
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 20/11/2009 Português
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The Knoevenagel condensation between aromatic aldehydes and malononitrile, ethyl cyanoacetate or malonic acid with hydroxyapatite supported caesium carbonate in water is described. HAP–Cs2CO3 was found to be a highly active, stable and recyclable catalyst under the reaction conditions.

‣ Chitosan as a Renewable Heterogeneous Catalyst for the Knoevenagel Reaction in Ionic Liquid as Green Solvent

Phan, Nam T. S.; Le, Ky K. A.; Nguyen, Thien V.; Le, Nhan T. H.
Fonte: International Scholarly Research Network Publicador: International Scholarly Research Network
Tipo: Artigo de Revista Científica
Publicado em 17/07/2012 Português
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The combination of chitosan as a renewable heterogeneous catalyst and ionic liquid as a “green” solvent was employed for the Knoevenagel reaction. The chitosan catalyst was characterized by various techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and elemental analysis. Excellent conversions were achieved under mild conditions without the need for an inert atmosphere. There was no contribution from leached active species, and conversion was only being possible in the presence of the solid catalyst. The chitosan catalyst as well as the ionic liquid solvent could be recovered in essentially pure form after being used in the reaction, and each of them could be reused several times without a significant degradation in efficiency.

‣ An Efficient and Recyclable Ionic Liquid-Supported Proline Catalyzed Knoevenagel Condensation

Zhuo, Chen; Xian, Dong; Jian-wei, Wu; Hui, Xie
Fonte: International Scholarly Research Network Publicador: International Scholarly Research Network
Tipo: Artigo de Revista Científica
Publicado em 10/04/2011 Português
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The Knoevenagel condensation reaction of aldehydes with malononitrile was described in this study, which was catalyzed by an efficient and recyclable ionic liquid-supported proline. The method represented an attractive alternative to the classical synthesis strategies and exhibited the advantage of performing homogeneous chemistry on a large scale additionally avoided large excesses of reagents. The products were obtained in good yields and reasonable purities without the need for further chromatographic purification. Moreover, the catalyst could be reused for at least four times.

‣ Preparation of neuroprotective condensed 1,4-benzoxazepines by regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction

Tóth, László; Fu, Yan; Zhang, Hai Yan; Mándi, Attila; Kövér, Katalin E; Illyés, Tünde-Zita; Kiss-Szikszai, Attila; Balogh, Balázs; Kurtán, Tibor; Antus, Sándor; Mátyus, Péter
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 06/11/2014 Português
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Condensed O,N-heterocycles containing tetrahydro-1,4-benzoxazepine and tetrahydroquinoline moieties were prepared by a regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction of a 4-aryl-2-phenyl-1,4-benzoxazepine derivative obtained from flavanone. The relative configuration of products were determined by the correlation of 3 J H,H coupling data with the geometry of major conformers accessed by DFT conformational analysis. Separated enantiomers of the products were characterized by HPLC-ECD data, which allowed their configurational assignment on the basis of TDDFT-ECD calculation of the solution conformers. Two compounds showed neuroprotective activities against hydrogen peroxide (H2O2) or β-amyloid25–35 (Aβ25–35)-induced cellular injuries in human neuroblastoma SH-SY5Y cells in the range of those of positive controls.

‣ Bifunctional Mesoporous Carbon Nitride: Highly Efficient Enzyme-like Catalyst for One-pot Deacetalization-Knoevenagel Reaction

Zhong, Lin; Anand, Chokkalingam; Lakhi, Kripal Singh; Lawrence, Geoffrey; Vinu, Ajayan
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 05/08/2015 Português
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Recently, mesoporous carbon nitride (MCN) has aroused extensive interest for its potential applications in organocatalysis, photo- and electrochemistry and CO2 capture. However, further surface functionalization of MCN for advanced nanomaterials and catalysis still remains very challenging. Here we show that acidic carboxyl groups can be smoothly introduced onto the surface of well-ordered MCN without annihilation between the introduced acid groups and MCN’s inherent basic groups through a facile UV light oxidation method. The functionalization generates a novel bifunctional nanocatalyst which offers an enzyme-like catalytic performance in the one-pot deacetalization-Knoevenagel reaction of benzaldehyde dimethylacetal and malononitrile with 100% conversion and more than 99% selectivity due to the cooperative catalysis between the acid and base groups separated on the surface of the catalyst. The results provide a general method to create multifunctional nanomaterials and open new opportunities for the development of high efficient catalyst for green organic synthesis.

‣ Synthesis and elaboration of peptidomimetic units

RAMADORI, FEDERICO
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
Português
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Retro-peptides are peptidomimetics that present the direction of the amino acidic sequence reversed. A classical retro modification can be obtained by the introduction of the malonyl unit followed by a gem-diaminic unit, that can result in an increase of proteolysis resistance of the related parent peptide, retarding degradation and consequently enhancing therapeutic efficacy.This thesis aims at developing synthetic stategies to synthesize new interesting building blocks for the construction of peptidomimetics containing a retro modification.In this field Meldrum’s acid is recently reported as a useful scaffold to obtain non-symmetric disubstituted malonamides rAA-mGly-AA′ as building blocks for the synthesis of retro-peptides. The attention has been turned towards the synthetic elaboration of different rAA-mGly-AA′ with the aim of introducing, into the malonamide backbone, the olefinic moiety by a Knoevenagel condensation, obtaining correspondig malonyl dehydro peptides MDHPs.The investigation of a further elaboration was carried out to obtain the corresponding epoxy and aziridino peptides,interesting building blocks containing electrophilic sites known to react with nucleophilic amino acids within the active site of proteases. Starting from L-amino acids...

‣ Estudo do uso de líquidos iônicos na síntese e biorredução de cetonas 'alfa', 'beta'-insaturadas; Study on the application of ionic liquids in the synthesis and bioreduction of 'alpha', 'beta'-unsaturated ketones

Bruno Ricardo Silva de Paula
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 17/07/2012 Português
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Nesse projeto investigou-se o uso de líquidos iônicos na preparação de compostos carbonílicos a,b-insaturados por meio da condensação de Knoevenagel e na biorredução dos produtos sintetizados. Na primeira etapa do projeto, estudou-se a aplicação de um protocolo desenvolvido pelo grupo de pesquisa para a condensação de Knoevenagel entre b-cetoésteres e aldeídos aromáticos em líquidos iônicos. Utilizaram-se os líquidos iônicos [bmim(PF6)] e [bmim(NTf2)], e em ambos os casos, obtiveram-se rendimentos de moderado a alto para as condensações envolvendo o acetoacetato de etila e o 4-cloroacetoacetato de etila. Os produtos obtidos, que em todos os casos foram misturas de diastereoisômeros, foram separados e caracterizados individualmente, e a configurações das olefinas (E ou Z) puderam ser determinadas com base na cristalografia de raios-X de dois dos compostos preparados, e posterior comparação dos espectros de RMN de C de todos os compostos sintetizados. O acetoacetato de etila forneceu como isômero majoritário o Z, enquanto o 4-cloroacetoacetato de etila forneceu como isômero majoritário o E. Na segunda etapa do projeto, estudaram-se as biorreduções dos compostos preparados em sistemas bifásicos água/líquido iônico hidrofóbico. Em geral...

‣ Condensação de Knoevenagel de aldeídos aromáticos com o ácido de Meldrum em água: uma aula experimental de Química Orgânica Verde

Cunha,Silvio; Santana,Lourenço Luis Botelho de
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 Português
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This work describes an undergraduate experiment for the synthesis of Knoevenagel adduct of Meldrum's acid with nine aromatic aldehydes, using water as the solvent, in an adaptation of a previously reported synthetic protocol. The synthesis was straightforward, requiring a period of two hours, and is suitable for undergraduate experimental courses on green chemistry. In addition, quantitative analyses of the relative reactivity of p-nitro-benzaldehyde and p-metoxi-benzaldehyde was evaluated through the competitive reaction of equimolar amounts of these aldehydes with one equivalent of Meldrum's acid, using gas chromatography to quantify the composition of the reaction mixture.