We gratefully acknowledge the Swedish Research Council Formas for generous financial support.

1. Síntese Gram-escala de metil-6-oxo-l, 3,4,6-triphenylhexanoate <ol><li> Seco 1-etil-3-metil imidazólio de etilo (EMIMAc) em um balão de fundo redondo sobre um evaporador rotativo a 10 mbar, 40 ° C durante 1 h. </li><li> Adicionar 2,1 g de EMIMAc seco e 1,0 g de 1,3-difenil-2-propen-1-ona A uma balão de 100 ml de fundo redondo equipado com um agitador magnético. </li><li> Adicionar 2,019 ml de metanol e 2,3 g de cinamaldeído para o balão. </li><li> À temperatura ambiente (22 ° C) dissolver a mistura em 60 ml de diclorometano por agitao durante 1 min. </li><li> Subsequentemente adiciona 0,37 ml de 1,8-diazabiciclo [5.4.0] undec-7-eno (DBU) à mistura em agitação (passo 1.4) e a tampa do frasco de fundo redondo. </li><li> Agita-se com uma barra de agitação magnética, a uma velocidade de 500 rpm à temperatura ambiente (22 ° C). </li><li> Verificar se completar a reacção com 1 H-RMN. 24 olhar para o desaparecimento da ligação dupla do chalcona na área de 7,8 ppm. </li><li> Quando a reacção atingiu<html> conclusão remover os voláteis num evaporador rotativo a 10 mbar, 20 ° C durante 15 min. </li><li> Adicionar 50 ml de metanol ao resíduo para o dissolver EMIMAc por agitação com uma barra de agitação magnética. </li><li> Remover os sólidos a partir das paredes do balão por agitação violenta com uma barra de agitação magnética, a uma velocidade de 750 rpm durante 30 min. Se necessário, utilizar uma espátula para remover os sólidos restantes das paredes. </li><li> Filtra-se a mistura sobre um filtro poroso (dimensão de poro 3). </li><li> Lava-se com 20 ml adicionais de metanol. Se a reciclagem do EMIMAc é desejado evaporar o filtrado metanólico. (passo 2.1). </li><li> Ainda sobre a frita, dividir suavemente o bolo de filtração (a partir do passo 1.11) em pedaços pequenos com uma espátula e transferir os sólidos através de um funil de pó para um balão de fundo redondo pré-pesados ​​e secar os sólidos sob vácuo. </li><li> Pesa-se o balão e o cálculo do rendimento. </li><li> Analisar o produto por RMN de 1 H (passo 1.7). Compare com espectros relatado 24. </li></ol>title &quot;&gt; 2. Reciclagem de EMIMAc <ol><li> Remover os voláteis a partir da mistura de metanol (a partir do passo 1.12) sob pressão reduzida de 10 mbar, a 40 ° C durante 30 min. </li><li> 24 Analisar o óleo resultante por 1 H RMN e 13 C RMN para verificar se está presente EMIMAc. </li><li> Use a EMIMAc reciclado a partir do passo 1.2. </li></ol> 3. Gelation <ol><li> Preparação de uma solução stock <ol><li> Adicionar 200 mg de metil-6-oxo-l, 3,4,6-triphenylhexanoate (o produto do passo 1.15) e uma barra de agitação magnética a um frasco. Adicionar 2,0 ml de diclorometano para dissolver o cetoéster. Mexa até que tudo se dissolva. </li></ol></li><li> Gelificação <ol><li> Adicionar 50 ml de heptano a um copo de 500 ml. Adicionar 1,5 ml de solução de estoque para o heptano. Agita-se rapidamente para assegurar uma mistura adequada e deixe repousar sem agitação à temperatura ambiente até que a gelificação ocorre. </li></ol></li></ol>

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The authors have nothing to disclose.

Com base na configuração- anti determinado por análise de raios-X de cetoéster 3 e na investigação mecanicista proposto por Bode e colegas de trabalho 30 o seguinte caminho reaccional é sugerido (Figura 5). A desprotonação do IL gera espécies NHC; o NHC reage com o aldeído insaturado, para formar o intermediário I. O Breslow Breslow intermédia e a calcona reagir numa reacção cruzada benzoína para formar dieno II. Intermediário II sofre um rearranjo oxi-Cope via estad...

<img alt="TOC 1" src="/files/ftp_upload/53213/53213TOC.jpg" /> (Acima) síntese Três-componente do 1,6-cetoésteres: uma nova classe de gelators baixo peso molecular. Os líquidos iónicos (ILS) têm uma elevada estabilidade, baixa volatilidade, não inflamabilidade e, portanto, têm prestado atenção como meios de reacção seguras e solventes ideais para reciclagem. 1-3 imidazoliums dialquilo é um certo tipo de líquidos iónicos que, na presença de uma base, , pode ser desprotonado para renderizar um carbeno N-heterocíclicos (NHC) 4. No campo da organocatálise, NHCs, operando sob caminhos de reação distintas, têm encontrado uso generalizado em uma ampla gama de reações genéricas. 5-11 Apesar disso, a ligação entre TIs e ligação CC forming NHC-catálise é relativamente inexplorado. No entanto, NHCs derivado de ILS têm sido relatados para catalisar reacções de formação de ligações CC, tais como a condensação de benzoína e a reacção Stetter 12-22. Por exemplo, Davis et ai. Demonstraram que LIs thiazoliums derivados de N-alquilo servir como no precatalysts 12 formação de benzoína do benzaldeído. Mais recentemente, Chen e colegas de trabalho expandido este conceito utilizando uma base imidazólio IL, 1-etil-3-metil imidazólio de etilo (EMIMAc), para efectuar a condensação de benzoína em 5-hidroximetilfurfural (HMF) para gerar 5,5 &#39;-di (hidroximetil) furoin (DHMF). 23 Dado que as TIs estão disponíveis comercialmente e oferecem uma forma barata de gerar NHCs, estávamos interessados ​​em investigar o que os outros tipos de reações ILs poderia realizar. Para este fim, descobriu-se que de dialquilo imidazoliums poderia ser usado eficientemente como precatalysts no additi formal de conjugadode aldeídos insaturados em a calconas (Figura 1) para dar 1,6-cetoésteres. A IL mais eficiente, EMIMAc, promove uma reacção altamente estereosselectiva entre cinamaldeído e chalcona. A reacção ocorre com elevada preferência pelo anti -diastereero e os 1,6-cetoésteres pode ser isolado com rendimentos de até 92%. 24,25,26 <img alt="figura 1" src="/files/ftp_upload/53213/53213fig1.jpg" /> Figura 1: IL-mediada de três componentes, além estereosselectiva de cinamaldeído a calcona.

<table><tbody><tr><td>1-ethyl-3-methyl imidazolium acetate</td><td>Aldrich</td><td>51053-100G-F</td><td>Produced by BASF &amp;ge;90%, dried on a rotary evaporated before use (10 mBar, 40 &amp;deg;C, 1 hr)&lt;br/&gt; CAS NUMBER: 143314-17-4</td></tr><tr><td>1,3-diphenyl-2-propen-1-one</td><td>Aldrich</td><td>11970-100G</td><td>98.0%&lt;br/&gt; CAS NUMBER: 94-41-7</td></tr><tr><td>trans-cinnamaldehyde&amp;nbsp;</td><td>Aldrich</td><td>C80687-25G</td><td>99%, stored under nitrogen prior to use&lt;br/&gt; CAS NUMBER: 14371-10-9</td></tr><tr><td>1,8-Diazobicyclo[5.4.0]undec-7-ene</td><td>Aldrich</td><td>139009-25G</td><td>98%&lt;br/&gt; CAS NUMBER: 6674-22-2</td></tr><tr><td>Methanol</td><td>Sigma-Aldrich</td><td>32213N-2.5L</td><td>puriss. P.a., ACS reagent, reag. ISO, reag. Ph. Eur. &amp;ge;99.8% (GC)&lt;br/&gt; CAS NUMBER: 67-56-1</td></tr><tr><td>Dichloromethane</td><td>Fischer Chemical</td><td>D/1852/17X</td><td>Analytic reagent grade, stabilized with amylene&lt;br/&gt; CAS NUMBER: 9/2/1975</td></tr><tr><td>n-Heptane</td><td>Fischer Chemical</td><td>H/0160/17X</td><td>Analytic reagent grade&lt;br/&gt; CAS NUMBER: 142-82-5</td></tr></tbody></table>

highly stereoselective synthesis of 1,6-ketoesters mediated by ionic liquids: a three-component reaction enabling rapid access to a new class of low molecular weight gelators

In organic chemistry ionic liquids (ILs) have emerged as safe and recyclable reaction solvents. In the presence of a base ILs can be deprotonated to form catalytically active N-Heterocyclic Carbenes (NHCs). Here we have used ILs as precatalysts in the addition of &#945;,&#946;-unsaturated aldehydes to chalcones to form 1,6-ketoesters, incorporating an anti-diphenyl moiety in a highly stereoselective fashion. The reaction has a broad substrate scope and several functional groups and heteroaromatics can be integrated into the ketoester backbone in generally good yields with maintained stereoselectivity. The reaction protocol is robust and scalable. The starting materials are inexpensive and the products can be obtained after simple filtration, avoiding solvent-demanding chromatography. Furthermore, the IL can be recycled up to 5 times without any loss of reactivity. Moreover, the 1,6-ketoester end product is a potent gelator in several hydrocarbon based solvents. The method enables rapid access to and evaluation of a new class of low molecular weight gelators (LMWGs) from recyclable and inexpensive starting materials.

Tal como exemplificado antes, EMIMAc servir como um pré-catalisador na adição conjugada de formal de α, β-aldeído insaturado de chalconas. Outros LIs disponíveis comercialmente imidazólio base, tais como cloreto de 1-etil-3-metilimidazólio (EMIMCl) e cloreto de 1-butil-3-metilimidazólio (BMIMCl) também foram investigados, no entanto, estas reacções decorreram de rendimentos mais baixos, indicando que o anião de etilo pode ser importante para a reactividade (Tabela 1, entra...

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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

Ionic liquids (ILs) mediate fast, simple and cheap access to 1,6-ketoesters in high diastereoselectivities and good yields. The reaction protocol is robust and the 1,6-ketoesters can be obtained in gram scale after a simple filtration protocol. Moreover, the 1,6-ketoesters are potent gelators in hydrocarbon solvents.

Síntese altamente Stereoselective de 1,6-cetoésteres Mediada por líquidos iônicos: A reacção de três componente permitindo o rápido acesso a uma nova classe de baixo peso molecular Gelators Peso

In organic chemistry ionic liquids (ILs) have emerged as safe and recyclable reaction solvents. In the presence of a base ILs can be deprotonated to form ...

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8.7K visualizações.  Chalmers University of Technology. Ionic liquids (ILs) mediate fast, simple and cheap access to 1,6-ketoesters in high diastereoselectivities and good yields. The reaction protocol is robust and the 1,6-ketoesters can be obtained in gram scale after a simple filtration protocol. Moreover, the 1,6-ketoesters are potent gelators in hydrocarbon solvents. 

Vídeo: Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol

The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous layer by generating a charged structure provides an opportunity to use extraction as a simple purification technique. By combining the use of a miscible organic solvent with saturated sodium bisulfite, aldehydes and reactive ketones can be successfully transformed into charged bisulfite adducts that can then be separated from other organic components of a mixture by the introduction of an immiscible organic layer. Here, we describe a simple protocol for the removal of aldehydes, including sterically-hindered neopentyl aldehydes and some ketones, from chemical mixtures. Ketones can be separated if they are sterically unhindered cyclic or methyl ketones. For aliphatic aldehydes and ketones, dimethylformamide is used as the miscible solvent to improve removal rates. The bisulfite addition reaction can be reversed by basification of the aqueous layer, allowing for the re-isolation of the reactive carbonyl component of a mixture.

Here, we present a protocol to remove aldehydes and reactive ketones from mixtures by a liquid-liquid extraction protocol directly with saturated sodium bisulfite in a miscible solvent. This combined protocol is rapid and facile to perform. The aldehyde or ketone can be re-isolated by the basification of the aqueous layer.

Separação de aldeídos e cetonas reativas de misturas usando um protocolo de extração de bissulfito

The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous layer ...

Química

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. Recently, we have developed a two-step strategy for ketone enolate umpolung that has enabled the development of methods for chlorination, azidation, and amination using azoles. In addition, we have developed C-C bond&#8211;forming arylation and allylation reactions. At the heart of these methods is the preparation of the intermediate and highly reactive enolonium species prior to addition of a reactive nucleophile. This strategy is thus reminiscent of the preparation and use of metal enolates in classical synthetic chemistry. This strategy allows the use of nucleophiles that would otherwise be incompatible with the strongly oxidizing hypervalent iodine reagents. In this paper we present a detailed protocol for chlorination, azidation, N-heteroarylation, arylation, and allylation. The products include motifs prevalent in medicinally active products. This article will greatly assist others in using these methods.

A two step one-pot protocol for the umpolung of ketone enolates to enolonium species and addition of a nucleophile to the &#945;-position is described. Nucleophiles include chloride, azide, azoles, allyl-silanes, and aromatic compounds.

Um Protocolo em Duas Etapas para Funcionalização de Umpolung de Cetonas via Espécies de Enolonium

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. ...

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and 1-methyl-4-(1,2,2-triiodovinyl)benzene as representative examples for the practical chemoselective preparation of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes from the chemoselective iodination of terminal alkynes mediated by hypervalent-iodine reagents. The chemoselectivity was confirmed by using p-tolylethyne as a model substrate to screen a variety of iodine sources and/or the hypervalent-iodine reagents. A combination of tetrabutylammonium iodide (TBAI) and (diacetoxyiodo)benzene (PIDA) selectively generates 1-iodoalkynes, while a combination of KI and PIDA generates 1,2-diiodoalkenes. A one-pot synthesis based on both TBAI-PIDA and KI-PIDA yields the corresponding 1,1,2-triiodoalkenes. These protocols were subsequently applied to the synthesis of synthetically important aromatic and aliphatic 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes, which were obtained in good yield with excellent chemoselectivity.

Herein, detailed protocols for the oxidative iodination of terminal alkynes using hypervalent-iodine reagents are presented, which chemoselectively afford 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes.

Preparação Quimiosseletiva de 1-iodoalquinos, 1,2-diiodoalqueenos e 1,1,2-triiodoalqueenos Baseada na Iodação Oxidativa de Alquinos Terminais

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and ...

Synthesis of Esters Via a Greener Steglich Esterification in Acetonitrile

The Steglich esterification is a widely-used reaction for the synthesis of esters from carboxylic acids and alcohols. While efficient and mild, the reaction is commonly performed using chlorinated or amide solvent systems, which are hazardous to human health and the environment. Our methodology utilizes acetonitrile as a greener and less hazardous solvent system. This protocol exhibits rates and yields that are comparable to traditional solvent systems and employs an extraction and wash sequence that eliminates the need for the purification of the ester product via column chromatography. This general method can be used to couple a variety of carboxylic acids with 1&#176; and 2&#176; aliphatic alcohols, benzylic and allylic alcohols, and phenols to obtain pure esters in high yields. The goal of the protocol detailed here is to provide a greener alternative to a common esterification reaction, which could serve useful for ester synthesis in both academic and industrial applications.

A modified Steglich esterification reaction was used to synthesize a small library of ester derivatives with primary and secondary alcohols. The methodology uses a non-halogenated and greener solvent, acetonitrile, and enables product isolation in high yields without the need for chromatographic purification.

Síntese de ésteres através de uma esterificação Steglich mais verde em acetonitrila

The Steglich esterification is a widely-used reaction for the synthesis of esters from carboxylic acids and alcohols. While efficient and mild, the ...

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of &#945;-Imino &#947;-Lactones and Alkylidene Pyrazolones

Bispirocyclic scaffolds are one of the important structural subunits in many natural products that exhibit diverse and attractive biological activities. Recently, we have developed an efficient organocatalytic strategy, which provides facile access to a variety of enantiomerically enriched bispiro[&#947;-butyrolactone-pyrrolidin-4,4&#39;-pyrazolone] skeletons. In this paper, we demonstrate a detailed protocol for the asymmetric synthesis of drug-like bispirocyclic compounds with two spirocyclic carbon centers via an organocatyltic 1,3-dipolar cycloaddition reaction. Spirocyclization synthons &#945;-imino &#947;-lactones and alkylidene pyrazolones are prepared first, which are then subjected to a cycloaddition reaction in the presence of a bifunctional squaramide organocatalyst to afford the desired bispirocycles in high yields and excellent stereoselectivities. Chiral high-performance liquid chromatography (HPLC) is carried out to determine the enantiomeric purity of the products, and the d.r. value is examined by proton nuclear magnetic resonance (1H NMR). The absolute configuration of the product is assigned according to an X-ray crystallographic analysis. This synthetic strategy allows scientists to prepare a diversity of bispirocyclic scaffolds in high yields and excellent diastereo- and enantioselectivities.

Enantiomerically enriched bispiro[&#947;-butyrolactone-pyrrolidin-4,4&#39;-pyrazolone] skeletons are asymmetrically synthesized through a simple organocatalytic 1,3-dipolar cycloaddition reaction.

Construção eficiente de andaimes de drogas, como Bispirocyclic Via Organocatalytic cicloadições de γ-lactonas α-Imino e pirazolonas Alkylidene

Bispirocyclic scaffolds are one of the important structural subunits in many natural products that exhibit diverse and attractive biological activities. ...

Efficient Synthesis of All-Carbon Quaternary Centers via the Conjugate Addition of Functionalized Monoorganozinc Bromides

The conjugate addition of organometallic reagents to &#945;,&#946;-unsaturated carbonyls represents an important method to generate C&#8211;C bonds in the preparation of all-carbon quaternary centers. Though conjugate additions of organometallic reagents are typically performed utilizing highly reactive organolithium or Grignard reagents, organozinc reagents have garnered attention for their enhanced chemoselectivity and mild reactivity. Despite numerous recent advances with more reactive diorganozinc and mixed diorganozinc reagents, the generation of all-carbon quaternary centers via the conjugate addition of functionalized monoorganozinc reagents remains a challenge. This protocol details a convenient and mild &#8220;one-pot&#8221; preparation and copper mediated conjugate addition of functionalized monoorganozinc bromides to cyclic &#945;,&#946;-unsaturated carbonyls to afford a broad scope of all-carbon quaternary centers in generally excellent yield and diastereoselectivity. Key to the development of this technology is the utilization of DMA as a reaction solvent with TMSCl as a Lewis acid. Notable advantages to this methodology include the operational simplicity of the organozinc reagent preparation afforded by the utilization of DMA as a solvent, as well as an efficient conjugate addition mediated by various Cu(I) and Cu(II) salts. Moreover, an intermediate silyl enol ether can be isolated utilizing a modified workup procedure. The substrate scope is limited to cyclic unsaturated ketones, and the conjugate addition is impeded by stabilized (e.g., allyl, enolate, homoenolate) and sterically encumbered (e.g., neopentyl, o-aryl) monoorganozinc reagents. Conjugate additions to five- and seven-membered rings were effective, albeit in lower yields compared with six-membered ring substrates.

A simple and practical protocol for the efficient conjugate addition of functionalized monoorganozinc bromides to cyclic &#945;,&#946;-unsaturated carbonyls to furnish all-carbon quaternary centers was developed.

Síntese eficiente de todos os centros quaternários de carbono através da adição conjugada de brometos Monoorganozinc funcionalizados

The conjugate addition of organometallic reagents to &#945;,&#946;-unsaturated carbonyls represents an important method to generate C&#8211;C bonds in the ...

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products and notably to generate chiral carbon centers. The crucial first step consists in the selective double hydroboration of CO2 catalyzed by an iron hydride complex. The product obtained with this 4 e- reduction is a rare bis(boryl)acetal, compound 1, which is subjected in situ to three different reactions in a second step. The first reaction concerns a condensation reaction with (diisopropyl)phenylamine affording the corresponding imine 2. In the second and third reaction, intermediate 1 reacts with triazol-5-ylidene (Enders&#39; carbene) to afford compounds 3 or 4, depending on the reaction conditions. In both compounds, C-C bonds are formed, and chiral centers are generated from CO2 as the only source of carbon. Compound 4 exhibits two chiral centers obtained in a diastereoselective manner in a formose-type mechanism. We proved that the remaining boryl fragment plays a key role in this unprecedented stereocontrol. The interest of the method stands on the reactive and versatile nature of 1, giving rise to various complex molecules from a single intermediate. The complexity of a two-step method is compensated by the overall short reaction time (2 h for the larger reaction time), and mild reaction conditions (25 &#176;C to 80 &#176;C and 1 to 3 atm of CO2).

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations are conducted in a one-pot two-step procedure for the synthesis of complex molecules. The selective 4 e- reduction of CO2 with a hydroborane reductant affords a reactive and versatile bis(boryl)acetal intermediate which is subsequently involved in condensation reaction or carbene-mediated C-C coupling generation.

Transformações versáteis de CO2 em produtos complexos: uma estratégia de duas etapas de um pote

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products ...

Organocatalysis

Source: Vy M. Dong and Faben Cruz, Department of Chemistry, University of California, Irvine, CA
This experiment will demonstrate the concept of organocatalysis by illustrating the proper setup of a reaction that utilizes enamine catalysis. Organocatalysis is a form of catalysis that uses substoichiometric amounts of small organic molecules to accelerate reactions. This type of catalysis is complementary to other forms of catalysis such as transition metal or biocatalysis. Transition metal catalysis involves transition metals as catalysts and biocatalysis uses enzymes as catalysts. Some advantages of organocatalysis include the low toxicity and cost of the organocatalysts in comparison to many metal catalysts. In addition, most organocatalysts are not sensitive to air and moisture, unlike metal catalysts. In contrast to enzymes found in living organisms, the small molecules that act as organocatalysts are typically easy to access. Furthermore, organocatalysis offers complementary and new reactivity not observed with other forms of catalysis.

Organocatalysis: Principles and Applications

Organocatálise

Source: Vy M. Dong and Faben Cruz, Department of Chemistry, University of California, Irvine, CA
This experiment will demonstrate the concept of ...

Education

JoVE Science Education

Química Orgânica II

&alpha;-Hydroxy Ketones via Reductive Coupling of Esters: Acyloin Condensation Overview

The pinacol and McMurry reactions involve the reductive coupling of ketones or aldehydes. Similarly, the bimolecular reductive coupling of two ester molecules in the presence of sodium metal in an aprotic solvent yields an &#945;-hydroxy ketone product. The &#945;-hydroxy ketone is also called acyloin, so the reaction is referred to as &#8216;acyloin condensation.&#8217;
<img alt="Figure1" src="/files/ftp_upload/12908/12908_PT_Figure_1.svg" style="text-align: center; height: 65px;" />
In the acyloin condensation reaction, esters are converted to ketyls, which undergo radical dimerization to form an unstable tetrahedral intermediate. Further, this intermediate collapses to give a 1,2-diketone intermediate. The 1,2-diketones are comparatively more reactive than ketones towards electrophiles and reducing agents because of lower &#960;* energy. Consequently, two electrons sequentially transfer to the 1,2-diketone to form an enediolate. Lastly, the enediolate intermediate is quenched with acid to yield an &#945;-hydroxy ketone with a good yield.
Often some by-products are obtained alongside the major product because of the reactivity of nucleophilic enediolate. To overcome the side reactions and improve the yield of an acyloin, trimethylsilyl chloride is used to silylate the enediolate. This results in a bis-silyl ether, further hydrolyzed with aqueous acid to give &#945;-hydroxy ketones.

&amp;#945;-Hydroxy Ketones via Reductive Coupling of Esters: Acyloin Condensation Overview

α-Hidroxicetonas via Acoplamento Redutor de Ésteres: Visão Geral da Condensação de Aciloína

The pinacol and McMurry reactions involve the reductive coupling of ketones or aldehydes. Similarly, the bimolecular reductive coupling of two ester ...

JoVE Core

Química orgânica

Unidade 1

Radicais

TERMOS E CONCEITOS CHAVE

&alpha;-Alkylation of Ketones via Enolate Ions

Ketones with &alpha; protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the &#945; carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the &#945;&nbsp;carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the strong interaction of the positive counterpart of the base with the anionic oxygen, which restricts the approaching electrophile, making the reaction less favorable. Also, the product obtained through C-attack is more stable than that obtained through O-&NoBreak;attack, as the stronger C=O &#960; bond is retained in the former, whereas a weaker C=C &#960; bond is preserved in the latter.
A subsequent reaction of the enolate with electrophiles such as alkyl halides produces an &#945;-alkylated ketone via the SN2 pathway. The &#945;-alkylation of ketones is achieved with the halides of primary alkyl, benzyl, and allylic groups. With secondary and tertiary alkyl halides, elimination predominates over substitution.

Síntese altamente Stereoselective de 1,6-cetoésteres Mediada por líquidos iônicos: A reacção de três componente permitindo o rápido acesso a uma nova classe de baixo peso molecular Gelators Peso

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