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

1. Gramm-Maßstab Synthese von Methyl-6-oxo-3,4,6-triphenylhexanoate <ol><li> Trocken 1-Ethyl-3-methyl-imidazolium-acetat (EMIMAc) in einem Rundkolben am Rotationsverdampfer bei 10 mbar, 40 ° C für 1 Stunde. </li><li> Hinzufügen von 2,1 g Trocken EMIMAc und 1,0 g 1,3-Diphenyl-2-propen-1-on Zu einer 100 ml-Rundkolben mit einem Magnetrührer ausgestattet war. </li><li> Hinzufügen 2,019 ml Methanol und 2,3 g Zimtaldehyd in den Kolben. </li><li> Bei Raumtemperatur (22 ° C) auflösen des Gemisches in 60 ml Dichlormethan unter Rühren für 1 min. </li><li> Anschließend fügen 0,37 ml 1,8-Diazabicyclo [5.4.0] undec-7-en (DBU) zu dem gerührten Gemisch (Schritt 1.4) und der Rundkolben begrenzen. </li><li> Zugegeben und mit einem Magnetrührer bei einer Drehzahl von 500 Umdrehungen pro Minute bei Raumtemperatur (22 ° C). </li><li> Überprüfen Beendigung der Reaktion mit 1 H-NMR. 24 Suchen Sie nach Verschwinden der Doppelbindung des Chalcon in der 7,8 ppm-Bereich. </li><li> Wenn die Reaktion erreicht hat<html> Abschluss Die flüchtigen Bestandteile werden am Rotationsverdampfer bei 10 mbar, 20 ° C für 15 min. </li><li> 50 ml Methanol zu dem Rückstand, um die EMIMAc durch Rühren mit einem magnetischen Rührstab aufzulösen. </li><li> Entfernen der Feststoffe von den Wänden des Kolbens durch Rühren heftig mit einem Magnetrührer bei einer Drehzahl von 750 Upm für 30 min. Falls erforderlich, verwenden Sie einen Spachtel, um verbleibenden Feststoffe von den Wänden entfernen. </li><li> Das Gemisch wird auf einer Fritte (Porengröße 3). </li><li> Mit zusätzlichen 20 ml Methanol waschen. Ist eine Wiederverwertung des EMIMAc gewünscht verdampfe das methanolische Filtrat. (Schritt 2.1). </li><li> Noch auf der Fritte, sanft teilen den Filterkuchen (aus Schritt 1.11) in kleinere Stücke mit einem Spatel und übertragen die Feststoffe über einen Pulvertrichter in eine vorgewogene Rundkolben gegeben und die Feststoffe unter Vakuum filtriert. </li><li> Wiegen Sie die Kolben und die Berechnung der Ausbeute. </li><li> Analysieren Sie das Produkt durch 1 H-NMR (Schritt 1.7). Vergleichen mit berichteten Spektren. 24 </li></ol>title &quot;&gt; 2. Recycling von EMIMAc <ol><li> Entfernen der flüchtigen Stoffe aus der methanolischen Mischung (aus Schritt 1.12) unter vermindertem Druck von 10 mbar, bei 40 ° C für 30 min. </li><li> Analysieren Sie die erhaltene Öl durch 1 H-NMR und 13 C-NMR, um zu überprüfen, dass EMIMAc vorhanden ist. 24 </li><li> Verwenden Sie das recycelte EMIMAc ab Schritt 1.2. </li></ol> 3. Die Gelierung <ol><li> Herstellung einer Stammlösung <ol><li> 200 mg Methyl-6-oxo-3,4,6-triphenylhexanoate (das Produkt von Schritt 1.15), und einem magnetischen Rührstab in ein Fläschchen. 2,0 ml Dichlormethan, um die Ketoester aufzulösen. Rühren bis alles gelöst ist. </li></ol></li><li> Gelierung <ol><li> 50 ml Heptan in einen 500 ml Becher. 1,5 ml der Stammlösung zu dem Heptan. Rühren Sie schnell auf eine ausreichende Durchmischung zu gewährleisten und stehen lassen, ohne Rühren bei Raumtemperatur, bis Gelierung auftritt. </li></ol></li></ol>

<ol>
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The authors have nothing to disclose.

Bezogen auf die anti-Konfiguration durch Röntgenanalyse -Ketoester 3 und auf der Untersuchung des Reaktionsmechanismus von Bode et al vorgeschlagenen 30 bestimmt die folgenden Reaktionspfad vorgeschlagen (Figur 5). Deprotonierung des IL erzeugt NHC Arten; das NHC reagiert mit dem ungesättigten Aldehyds der Breslow-Intermediat I. Der Breslow-Intermediat zu bilden, und die Chalcon reagieren in einer Quer Benzoin Reaktion auf Dien II bilden. Mittelstufe II durchläuft eine Oxy-Cope-Um...

<img alt="TOC 1" src="/files/ftp_upload/53213/53213TOC.jpg" /> (Oben) Drei-Komponenten-Synthese von 1,6-Ketoestern: eine neue Klasse von Gewichts Gelatoren niedrigem Molekulargewicht. Ionische Flüssigkeiten (ILs) eine hohe Stabilität, geringe Volatilität, nicht-entflammbar und daher als sicher Reaktionsmedien und ideale Lösungsmittel für Recycling gemacht Aufmerksamkeit. 1-3 Dialkyl imidazoliums sind eine bestimmte Art von ionischen Flüssigkeiten, die, in der Gegenwart einer Base kann deprotoniert, um ein N-heterocyclisches Carben (NHC). 4 Auf dem Gebiet der Organokatalyse übertragen werden, NHCs, die unter verschiedenen Reaktionswegen, haben eine weit verbreitete Nutzung in einer breiten Palette von generischen Reaktionen gefunden. 5-11 Trotz dieser, die Verbindung zwischen ILs und CC-Bindung forming NHC-Katalyse ist relativ unerforscht. Dennoch NHC von ILs abgeleitet wurde berichtet, dass CC-Bindung bildenden Reaktionen wie der Benzoinkondensation und die Stetter-Reaktion katalysieren. 12-22 beispielsweise Davis et al. Haben gezeigt, dass IL aus N-Alkyl Thiazoliumgruppen abgeleitet dienen als Präkatalysatoren in der Bildung Benzoin aus Benzaldehyd. 12 In jüngerer Zeit, Chen et al erweitert dieses Konzept unter Verwendung eines Imidazolium basierend IL, 1-Ethyl-3-methyl-imidazolium-acetat (EMIMAc), um die Benzoinkondensation von 5-Hydroxymethylfurfural (HMF) durch, um zu generieren 5,5 &#39;-di (hydroxymethyl) Furoin (DHMF). 23 Da ILs sind kommerziell erhältlich und bieten eine kostengünstige Möglichkeit der Erzeugung von NHCs, waren wir an die Untersuchung, was andere Arten von Reaktionen ILs durchführen könnte. Zu diesem Zweck haben wir festgestellt, daß Dialkylcarbonate imidazoliums könnte effizient wie Präkatalysatoren in der formalen Konjugat additi verwendet werdenon von ungesättigten Aldehyden Chalkone (Abbildung 1), was 1,6-Ketoester. Die effizienteste IL, EMIMAc, fördert eine hoch stereoselektive Reaktion von Zimtaldehyd und Chalkon. Die Umsetzung erfolgt mit hoher Präferenz für das anti-Diastereomer und die 1,6-Ketoester in Ausbeuten bis zu 92% isoliert werden. 24,25,26 <img alt="Abbildung 1" src="/files/ftp_upload/53213/53213fig1.jpg" /> Abbildung 1: IL-vermittelte dreikomponentigen, stereoselektive Addition von Zimtaldehyd zu Chalkon.

<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.

Wie oben beispielhaft, EMIMAc dienen als Präkatalysator in der formalen konjugierte Addition von α, β-ungesättigten Aldehyd zu Chalkone. Andere im Handel erhältliche imidazolium IFs wie 1-Ethyl-3-methylimidazolium Chlorid (EMIMCl) und 1-Butyl-3-methylimidazolium Chlorid (BMIMCl) wurden ebenfalls untersucht, jedoch sind diese Reaktionen geringere Ausbeuten anzeigt, dass das Acetatanion sein kann gangen 27,28 * wichtig für die Reaktivität (Tabelle 1, 1-3). <p class="...

Watch this Scientific Journal Video about 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

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.

Hochstereoselektive Synthese von 1,6-Ketoester durch Ionische Flüssigkeiten vermittelte: Ein Dreikomponentenreaktion zur raschen Zugang zu einer neuen Klasse von niedermolekularen Gelbildner

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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JoVE Journal

Chemistry

8.7K Aufrufe.  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. 

Serie: 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.

Trennung von Aldehyden und reaktive Ketone von Mischungen mit einem Bisulfit-Extraktion-Protokoll

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

Forschung

Chemie

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.

Ein zweistufiges Protokoll für die Umpolung Funktionalisierung von Ketonen über Enolonium Arten

&#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.

Chemische Herstellung von 1-Iodoalkynes, 1,2-Diiodoalkenes und 1,1,2-Triiodoalkenes basierend auf den oxidativen Jodierung von Terminal Alkinen

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.

Synthese von Estern über ein grüner Steglich-Veresterung in Acetonitril

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.

Energieeffizientes bauen Drogen wie Bispirocyclic Gerüste über Organocatalytic Cycloadditions von α-Imino γ-Lactone und Alkylidene Pyrazolones

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.

Effiziente Synthese von All-Carbon-Quaternärszentren über die Conjugate-Ergänzung der funktionalisierten monoorganozinischen Bromides

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.

Vielseitige CO 2-Transformationen in komplexe Produkte: Eine Zwei-Schritte-Strategie

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

Organokatalyse

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

Lehre

JoVE Science Education

Organische Chemie 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-Hydroxyketone durch reduktive Kupplung von Estern: Überblick über die Acyloin-Kondensation

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

JoVE Core

Organische Chemie

Unit 1

Radikalchemie

SCHLÜSSELBEGRIFFE UND KONZEPTE

&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.