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Organocatálise em CO2 supercrítico: reatividade e otimização de processo; Organocatalysis in supercritical CO2: reactivity and process optimization.

Cassaro, Rafael Frascino
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 14/05/2015 Português
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O dióxido de carbono no estado supercrítico (CO2-SC) tem despertado considerável interesse nos últimos anos como um novo solvente para reações orgânicas. Nesta tese foi investigada a influência do uso de CO2 supercrítico, associado ou não a líquidos iônicos ou cossolventes, como solvente em reações químicas visando à obtenção de precursores quirais. Foram estudadas as reações de condensação Aldólica, de Morita-Baylis-Hillman (MBH) e do tipo adição de Michael, empregando Organocatálise quando conveniente, isto é, catalisadores provenientes de aminoácidos e ácidos carboxílicos. As reações de MBH foram otimizadas através de um planejamento experimental e sua condição ótima se deu a 70°C, 110 bar, com 6 equivalentes de H2O, tempo reacional de 2h30 min e sem a presença de liquido iônico, tendo um rendimento de 84,6%. Para as condensações aldólicas os melhores resultados com acetona e p-nitrobenzaldeido como materiais de partida foram obtidos a 150 bar e 40°C, com a presença de liquido iônico, em 2 horas de tempo reacional com um rendimento de 54,0% e um excesso enantiomérico de 79,0% utilizando o catalisador (2S,4R)-4-(terc-butildimetilsililoxi)pirrolidina-2-ácido carboxílico. Com ciclohexanona como material de partida foram obtidos a 150 bar e 40°C com a presença de um doador de prótons (resina de troca iônica) em 2 horas de tempo reacional com um rendimento de 70...

Reações de organocatálise com aminas quirais: aspectos mecanísticos e aplicações em síntese orgânica

Amarante,Giovanni W.; Coelho,Fernando
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 philosophy of organocatalysis is based on the utilization of organic compounds to catalyze organic transformations without the intervention of metals. This area has attracted much attention of the synthetic chemistry community on the last years, which can be confirmed by the explosion of published papers dealing with this subject. Phosphorus compounds, urea and thiourea derivatives, alkaloids, guanidine derivatives, for example, have already been used as organocatalysts. In this review we have focused on the use of chiral amines as organocatalyst. We have also chosen some outstanding examples to demonstrate the potentiality of this strategy in the synthesis of natural products and biologically active compounds.

Merging Photoredox Catalysis with Organocatalysis: The Direct Asymmetric Alkylation of Aldehydes

Nicewicz, David A.; MacMilla, David W. C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Photoredox catalysis and organocatalysis represent two powerful fields of molecule activation that have found widespread application in the areas of inorganic and organic chemistry, respectively. We merged these two catalysis fields to solve problems in asymmetric chemical synthesis. Specifically, the enantioselective intermolecular α-alkylation of aldehydes has been accomplished using an interwoven activation pathway that combines both the photoredox catalyst Ru(bpy)3Cl2 (where bpy is 2,2′-bipyridine) and an imidazolidinone organocatalyst. This broadly applicable, yet previously elusive, alkylation reaction is now highly enantioselective and operationally trivial.

Autocatalysis and organocatalysis with synthetic structures

Kamioka, Seiji; Ajami, Dariush; Rebek, Julius
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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The discovery of ribozymes led to the proposal of an RNA world, where a single type of molecule was supposedly capable of self-replication and chemical catalysis. We show here that both autocatalysis and organocatalysis can be engineered into a synthetic structure. The compound is shown to selectively accelerate its own formation and catalyze either hydrogenation or nucleophilic addition to α,β-unsaturated aldehydes. The observed reactivity indicates that the components of a purported pre-RNA world conceivably include smaller organic molecules.

Simple strategy for synthesis of optically active allylic alcohols and amines by using enantioselective organocatalysis

Jiang, Hao; Holub, Nicole; Anker Jørgensen, Karl
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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A simple organocatalytic one-pot protocol for the construction of optically active allylic alcohols and amines using readily available reactants and catalyst is presented. The described reaction is enabled by an enantioselective enone epoxidation/aziridination-Wharton-reaction sequence affording two highly privileged and synthetically important classes of compounds in an easy and benign way. The advantages of the described sequence include easy generation of stereogenic allylic centers, also including quaternary stereocenters, with excellent enantio- and diastereomeric-control and high product diversity. Furthermore, using monosubstituted enones as substrates, having moderate enantiomeric excess, the one-pot reaction sequence proceeds with an enantioenrichment of the products and high diastereoselectivity was achieved.

Organocatalysis

Jacobsen, Eric N.; MacMillan, David W. C.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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The use of small-molecule organic catalysts in organic synthesis has flourished over the past decade. Examples of defining concepts and cutting-edge results are provided in the papers in this Special Feature.

Attractive noncovalent interactions in asymmetric catalysis: Links between enzymes and small molecule catalysts

Knowles, Robert R.; Jacobsen, Eric N.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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Catalysis by neutral, organic, small molecules capable of binding and activating substrates solely via noncovalent interactions—particularly H-bonding—has emerged as an important approach in organocatalysis. The mechanisms by which such small molecule catalysts induce high enantioselectivity may be quite different from those used by catalysts that rely on covalent interactions with substrates. Attractive noncovalent interactions are weaker, less distance dependent, less directional, and more affected by entropy than covalent interactions. However, the conformational constraint required for high stereoinduction may be achieved, in principle, if multiple noncovalent attractive interactions are operating in concert. This perspective will outline some recent efforts to elucidate the cooperative mechanisms responsible for stereoinduction in highly enantioselective reactions promoted by noncovalent catalysts.

Proline Sulfonamide-Based Organocatalysis: Better Late than Never

Yang, Hua; Carter, Rich G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/09/2010 Português
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The history of proline sulfonamides for use in catalyzing highly enantioselective and diastereoselective C-C bond forming reactions is described. Highlighted is the development of N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide (“Hua Cat”) and N-(carboxy-p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide (“Hua Cat-II”) by Yang and Carter. Specific reactions covered include the aldol reaction, Mannich reaction, formal aza-Diels-Alder reaction, tandem Michael/Mannich reaction and Yamada-Otani reaction. The ability of proline aryl sulfonamides to construct all-carbon quaternary stereocenters in high enantioselectivity and diastereoselectivity is a notable feature of the reported work. The practicality of this chemistry for large scale and industrial applications is also included. Finally, a discussion of the future directions of proline sulfonamide organocatalysis is provided.

A Diels-Alder Reaction Conducted Within the Parameters of Aqueous Organocatalysis: Still Just Smoke and Mirrors

Stowe, G. Neil; Janda, Kim D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 27/04/2011 Português
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Conducting reactions using water as solvent is a highly prized goal for the organic chemist. Based upon recent literature and our continuing interest in the field of aqueous organocatalysis, we tested the scope of an enamine based Diels-Alder reaction using (±)-nornicotine, proline and a proline derivative as aqueous organocatalysts. Unfortunately, none of the examined catalysts under aqueous conditions proved useful, leaving the aqueous Diels-Alder reaction as an elusive goal.

Enantioselective synthesis of C2-functionalized, N-protected morpholines and orthogonally N,N′-protected piperazines via organocatalysis

O’Reilly, Matthew C.; Lindsley, Craig W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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In this Letter, we describe a novel three-step, one-pot procedure for the enantioselective synthesis of N-benzyl protected morpholines and orthogonally N,N′-protected piperazines with chiral alkyl groups installed at the C2 position of each heterocyclic core via organocatalysis. This methodology allows for the rapid preparation of functionalized morpholines and piperazines that are not readily accessible through any other chemistry in good to excellent % ee (55–98% ee).

Mechanochemistry assisted asymmetric organocatalysis: A sustainable approach

Chauhan, Pankaj; Chimni, Swapandeep Singh
Fonte: Beilstein-Institut Publicador: Beilstein-Institut
Tipo: Artigo de Revista Científica
Publicado em 06/12/2012 Português
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Ball-milling and pestle and mortar grinding have emerged as powerful methods for the development of environmentally benign chemical transformations. Recently, the use of these mechanochemical techniques in asymmetric organocatalysis has increased. This review highlights the progress in asymmetric organocatalytic reactions assisted by mechanochemical techniques.

Direct β-Functionalization of Cyclic Ketones with Aryl Ketones via the Merger of Photoredox and Organocatalysis

Petronijević, Filip R.; Nappi, Manuel; MacMillan, David W. C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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The direct β-coupling of cyclic ketones with aryl ketones has been achieved via the synergistic combination of photoredox catalysis and organocatalysis. Diaryl oxymethyl or aryl–alkyl oxymethyl radicals, transiently generated via single-electron reduction of ketone precursors, readily merge with β-enaminyl radical species – generated by photon-induced enamine oxidation – to produce γ-hydroxyketone adducts. Experimental evidence indicates that two discrete reaction pathways can be operable in this process depending upon the nature of the ketyl radical precursor and the photocatalyst.

Asymmetric Organocatalysis at the Service of Medicinal Chemistry

Ricci, Alfredo
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em 11/03/2014 Português
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The application of the most representative and up-to-date examples of homogeneous asymmetric organocatalysis to the synthesis of molecules of interest in medicinal chemistry is reported. The use of different types of organocatalysts operative via noncovalent and covalent interactions is critically reviewed and the possibility of running some of these reactions on large or industrial scale is described. A comparison between the organo- and metal-catalysed methodologies is offered in several cases, thus highlighting the merits and drawbacks of these two complementary approaches to the obtainment of very popular on market drugs or of related key scaffolds.

Development of a general, enantioselective organocatalytic Mukaiyama–Michael reaction with α,β-unsaturated aldehydes

Borths, Christopher J.; Carrera, Diane E.; MacMillan, David W.C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/08/2009 Português
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LUMO-lowering organocatalysis has been extended to promote the conjugate addition of S-alkyl and -pyrrolyl silylketene acetals to α,β-unsaturated aldehydes, yielding both, syn and anti Mukaiyama–Michael products with high levels of enantioselectivity. This strategy allows for the generation of chemically useful 1,5-dicarbonyl systems and again highlights the utility of organocatalysis.

Attractive Noncovalent Interactions in Asymmetric Catalysis: Links Between Enzymes and Small Molecule Catalysts

Knowles, Robert R.; Jacobsen, Eric N.
Fonte: Proceedings of the National Academy of Sciences Publicador: Proceedings of the National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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27.2%
Catalysis by neutral, organic, small molecules capable of binding and activating substrates solely via noncovalent interactions—particularly H-bonding—has emerged as an important approach in organocatalysis. The mechanisms by which such small molecule catalysts induce high enantioselectivity may be quite different from those used by catalysts that rely on covalent interactions with substrates. Attractive noncovalent interactions are weaker, less distance dependent, less directional, and more affected by entropy than covalent interactions. However, the conformational constraint required for high stereoinduction may be achieved, in principle, if multiple noncovalent attractive interactions are operating in concert. This perspective will outline some recent efforts to elucidate the cooperative mechanisms responsible for stereoinduction in highly enantioselective reactions promoted by noncovalent catalysts.; Chemistry and Chemical Biology

Part I. asymmetric organocatalysis: 1. direct enantioselective organocatalytic hydroxymethylation of aldehydes catalyzed by α,α-diphenylprolinol trimethylsilyl ether: application in the formal synthesis of (-)-Rasfonin; 2. synthesis of a novel bicyclic secondary amine organocatalyst: application to the direct enantioselective organocatalytic hydroxymethylation of aldehydes Part II. asymmetric synthesis of bicyclic analogues of the anti-osteoporotic drug Risedronate; Asymmetric synthesis of bicyclic analogues of the anti-osteoporotic drug Risedronate; Asymmetric organocatalysis: 1. direct enantioselective organocatalytic hydroxymethylation of aldehydes catalyzed by α,α-diphenylprolinol trimethylsilyl ether: application in the formal synthesis of (-)-Rasfonin; 2. synthesis of a novel bicyclic secondary amine organocatalyst: application to the direct enantioselective organocatalytic hydroxymethylation of aldehydes Part II. asymmetric synthesis of bicyclic analogues of the anti-osteoporotic drug Risedronate; Part II. asymmetric synthesis of bicyclic analogues of the anti-osteoporotic drug Risedronate

Miller, John Robert (1982 - ); Boeckman, Robert K.
Fonte: University of Rochester. Publicador: University of Rochester.
Tipo: Tese de Doutorado Formato: Number of Pages:xxii, 364 leaves
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Thesis (Ph. D.)--University of Rochester. Dept. of Chemistry, 2010.; Part I. Asymmetric Organocatalysis: 1. Direct Enantioselective Organocatalytic Hydroxymethylation of Aldehydes Catalyzed by α,α-Diphenylprolinol Trimethylsilyl Ether: Application in the Formal Synthesis of (-)-Rasfonin; 2. Synthesis of a Novel Bicyclic Secondary Amine Organocatalyst: Application to the Direct Enantioselective Organocatalytic Hydroxymethylation of Aldehydes An efficient and synthetically useful enantioselective organocatalytic hydroxymethylation of aldehydes catalyzed by α,α-diphenylprolinol trimethylsilyl ether has been developed with excellent enantioselectivity and a broad substrate scope. The hydroxymethylation methodology was applied to a short formal synthesis of (-)-Rasfonin; an apoptosis inducer in ras dependent cells. Several novel camphor-based secondary amine catalysts were synthesized via addition of a Grignard reagent to an activated imine which was efficiently synthesized by treatment of a lactam with Cp2Zr(H)Cl. Moderate to good enantioselectivity (up to 80%) in the organocatalytic enantioselective hydroxymethylation reaction were achieved with these catalyst systems.

Part II. Asymmetric Synthesis of Bicyclic Analogues of the Antiosteoporotic Drug Risedronate An enantioselective synthesis of the potentially potent anti-osteoporotic drug 6...

NONCOVALENT BIFUNCTIONAL ORGANOCATALYSIS APPLIED TO THE ACHIEVEMENT OF CHIRAL EPOXIDES AND 1,2-DIOLS

PALUMBO, CHIARA
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
Português
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Palladium and organocatalysis: An excellent recipe for asymmetric synthesis

Fernández-Ibañez, M. Ángeles; Maciá, Beatriz; Alonso, Diego A.; Pastor, Isidro M.
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Português
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The dual activation of simple substrates by the combination of organocatalysis and palladium catalysis has been successfully applied in a variety of different asymmetric transformations. Thus, the asymmetric α-allylation of carbonyl compounds, α-fluorination of acyl derivatives, decarboxylative protonation of β-dicarbonyl compounds, cyclization reactions of alkynyl carbonyl compounds and β-functionalization of aldehydes have been efficiently achieved employing this double-catalytic methodology

Parts-per-million level loading organocatalysed enantioselective silylation of alcohols

Park, Sang Yeon; Lee, Ji-Woong; Song, Choong Eui
Fonte: Nature Pub. Group Publicador: Nature Pub. Group
Tipo: Artigo de Revista Científica
Publicado em 18/06/2015 Português
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The field of organocatalysis has blossomed over the past few decades, becoming an alternative to transition-metal catalysis or even replacing the realm of transition-metal catalysis. However, a truly powerful organocatalyst with a high turnover number (TON) and turnover frequency (TOF) while retaining high enantioselectivity is yet to be discovered. Similar to metal catalysis, extremely low catalyst loading (p.p.m. or p.p.b. levels) is the ultimate goal of the organocatalysis community. Herein we report a remarkable contribution in this context: 1 p.p.m. loading of a simple 1,1′-bi-2-naphthol-based organocatalyst was enough to achieve highly enantioselective silylation reactions of alcohols. The unprecedented TONs and excellent enantioselectivity are ascribed to the robustness of the catalyst and systematic cooperative hydrogen-bonding organocatalysis in a densely confined chiral space.

Development of a general, enantioselective organocatalytic Mukaiyama-Michael reaction with α,β-unsaturated aldehydes

Borths, Christopher J.; Carrera, Diane E.; MacMillan, David W. C.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; PeerReviewed Formato: application/pdf; application/msword
Publicado em 15/08/2009 Português
Relevância na Pesquisa
17.2%
LUMO-lowering organocatalysis has been extended to promote the conjugate addition of S-alkyl and 1-pyrrolyl silylketene acetals to α,β-unsaturated aldehydes, yielding both, syn and anti Mukaiyama–Michael products with high levels of enantioselectivity. This strategy allows for the generation of chemically useful 1,5-dicarbonyl systems and again highlights the utility of organocatalysis.