Name: 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
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1. Gram-scale Synthesis of Methyl 6-oxo-3,4,6-triphenylhexanoate
<ol>
	<li>Dry 1-ethyl-3-methyl imidazolium acetate (EMIMAc) in a round bottom flask on a rotary evaporator at 10 mBar, 40 &#176;C for 1 hr.</li>
	<li>Add 2.1 g of dry EMIMAc and 1.0 g of 1,3-diphenyl-2-propen-1-one to a 100 ml round bottom flask equipped with a magnetic stirrer.</li>
	<li>Add 2.019 ml of methanol and 2.3 g of cinnamaldehyde to the flask.</li>
	<li>At room temperature (22 &#176;C) dissolve the mixture in 60 ml of dichloromethane by stirrin...

<ol>
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G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Benzoin+condensation+in+imidazolium+based+room-temperature+ionic+liquids.">Benzoin condensation in imidazolium based room-temperature ionic liquids.</a> Chin. Chem. Lett. 16, 321-324 (2005).</li><li>Estager, J., L&#233;v&#234;que, J. M., Turgis, R., Draye, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solventless+and+swift+benzoin+condensation+catalyzed+by+1-alkyl-3-methylimidazolium+ionic+liquids+under+microwave+irradiation.">Solventless and swift benzoin condensation catalyzed by 1-alkyl-3-methylimidazolium ionic liquids under microwave irradiation.</a> J. Mol. Catal. A: Chem. 256, 261-264 (2006).</li><li>Estager, J., L&#233;v&#234;que, J. -. M., Turgis, R., Draye, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neat+benzoin+condensation+in+recyclable+room-temperature+ionic+liquids+under+ultrasonic+activation.">Neat benzoin condensation in recyclable room-temperature ionic liquids under ultrasonic activation.</a> Tetrahedron Lett. 48, 755-759 (2007).</li><li>Orsini, M., Chiarotto, I., Elinson, M. N., Sotgiu, G., Inesi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Benzoin+condensation+in+1,3-dialkylimidazolium+ionic+liquids+via+electrochemical+generation+of+N-heterocyclic+carbene.">Benzoin condensation in 1,3-dialkylimidazolium ionic liquids via electrochemical generation of N-heterocyclic carbene.</a> Electrochem. Commun. 11, 1013-1017 (2009).</li><li>Dunn, M. H., Cole, M. L., Harper, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+an+ionic+liquid+solvent+on+the+synthesis+of+[gamma]-butyrolactones+by+conjugate+addition+using+NHC+organocatalysts.">Effects of an ionic liquid solvent on the synthesis of [gamma]-butyrolactones by conjugate addition using NHC organocatalysts.</a> RSC Advances. 2, 10160-10162 (2012).</li><li>Kelemen, Z., Holloczki, O., Nagy, J., Nyulaszi, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+organocatalytic+ionic+liquid.">An organocatalytic ionic liquid.</a> Org. Biomol. Chem. 9, 5362-5364 (2011).</li><li>Yu, F. -. L., Zhang, R. -. L., Xie, C. -. X., Yu, S. -. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+thermoregulated+phase-separable+triazolium+ionic+liquids+catalysts+and+application+for+Stetter+reaction.">Synthesis of thermoregulated phase-separable triazolium ionic liquids catalysts and application for Stetter reaction.</a> Tetrahedron. 66, 9145-9150 (2010).</li><li>Aupoix, A., Vo-Thanh, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvent-free+synthesis+of+alkylthiazolium-based+ionic+liquids+and+their+use+as+catalysts+in+the+intramolecular+Stetter+reaction.">Solvent-free synthesis of alkylthiazolium-based ionic liquids and their use as catalysts in the intramolecular Stetter reaction.</a> Synlett. , 1915-1920 (2009).</li><li>Yu, F. -. L., Jiang, J. -. J., Zhao, D. -. M., Xie, C. -. X., Yu, S. -. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imidazolium+chiral+ionic+liquid+derived+carbene-catalyzed+conjugate+umpolung+for+synthesis+of+[gamma]-butyrolactones.">Imidazolium chiral ionic liquid derived carbene-catalyzed conjugate umpolung for synthesis of [gamma]-butyrolactones.</a> RSC Advances. 3, 3996-4000 (2013).</li><li>Liu, D., Zhang, Y., Chen, E. Y. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organocatalytic+upgrading+of+the+key+biorefining+building+block+by+a+catalytic+ionic+liquid+and+N-heterocyclic+carbenes.">Organocatalytic upgrading of the key biorefining building block by a catalytic ionic liquid and N-heterocyclic carbenes.</a> Green Chem. 14, 2738-2746 (2012).</li><li>Ta, L., Axelsson, A., Bijl, J., Haukka, M., Sund&#233;n, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ionic+Liquids+as+Precatalysts+in+the+Highly+Stereoselective+Conjugate+Addition+of+&#945;,&#946;-Unsaturated+Aldehydes+to+Chalcones.">Ionic Liquids as Precatalysts in the Highly Stereoselective Conjugate Addition of &#945;,&#946;-Unsaturated Aldehydes to Chalcones.</a> Chem. Eur. J. 20, 13889-13893 (2014).</li><li>Nair, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nucleophilic+Heterocyclic+Carbene+Catalyzed+Annulation+of+Enals+to+Chalcones+in+Methanol:+A+Stereoselective+Synthesis+of+Highly+Functionalized+Cyclopentanes.">Nucleophilic Heterocyclic Carbene Catalyzed Annulation of Enals to Chalcones in Methanol: A Stereoselective Synthesis of Highly Functionalized Cyclopentanes.</a> Org. Lett. 11, 2507-2510 (2009).</li><li>Ma, J., Huang, Y., Chen, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=N-Heterocyclic+carbene-catalyzed+(NHC)+three-component+domino+reactions:+highly+stereoselective+synthesis+of+functionalized+acyclic+&#1013;-ketoesters.">N-Heterocyclic carbene-catalyzed (NHC) three-component domino reactions: highly stereoselective synthesis of functionalized acyclic &#1013;-ketoesters.</a> Org. Biomol. Chem. 9, 1791-1798 (2011).</li><li>Domingo, L. R., Saez, J. A., Arno, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+DFT+study+on+the+NHC+catalysed+Michael+addition+of+enols+to+&#945;,&#946;-unsaturated+acyl-azoliums.+A+base+catalysed+C-C+bond-formation+step.">A DFT study on the NHC catalysed Michael addition of enols to &#945;,&#946;-unsaturated acyl-azoliums. A base catalysed C-C bond-formation step.</a> Org. Biomol. Chem. 12, 895-904 (2014).</li><li>Kaeobamrung, J., Mahatthananchai, J., Zheng, P., Bode, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+Enantioselective+Claisen+Rearrangement+Catalyzed+by+N-Heterocyclic+Carbenes.">An Enantioselective Claisen Rearrangement Catalyzed by N-Heterocyclic Carbenes.</a> J. Am. Chem. Soc. 132, 8810-8812 (2010).</li><li>Zweep, N., van Esch, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Functional Molecular Gels. , 1-29 (2014).</li><li>Chiang, P. -. C., Kaeobamrung, J., Bode, J. 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Based on the anti-configuration determined by X-ray analysis of ketoester 3 and on the mechanistic investigation proposed by Bode and co-workers30 the following reaction path is suggested (Figure 5). Deprotonation of the IL generates NHC species; the NHC reacts with the unsaturated aldehyde to form the Breslow intermediate I. The Breslow intermediate and the chalcone react in a cross-benzoin reaction to form diene II. Intermediate II undergoes an oxy-Cope rearrangement via boat transi...

<img alt="TOC 1" src="/files/ftp_upload/53213/53213TOC.jpg" />
(Above) Three-component synthesis of 1,6-ketoesters: a new class of low molecular weight gelators.

Ionic liquids (ILs) have high stability, low volatility, non-flammability and have therefore rendered attention as safe reaction media and ideal solvents for recycling.1-3 Dialkyl imidazoliums are a certain type of ionic liquids that, in the presence of a base, can be deprotonated to render an N-heterocyclic carbene (NHC).4 In the field of organocatalysis, NHCs, operating under distinct reaction paths, have found widespread usage in a broad range of generic reactions.5-11
Despite this, the connection between ILs and C-C bond forming NHC&#8211;catalysis is relatively unexplored. Nevertheless, NHCs derived from ILs have been reported to catalyze C-C bond forming reactions such as the benzoin condensation and the Stetter reaction.12-22 For example, Davis et al. have shown that ILs derived from N-alkyl thiazoliums serve as precatalysts in the formation of benzoin from benzaldehyde.12
More recently, Chen and co-workers expanded this concept using an imidazolium based IL, 1-ethyl-3-methyl imidazolium acetate (EMIMAc), to perform the benzoin condensation on 5-hydroxymethylfurfural (HMF) to generate 5,5&#8217;-di(hydroxymethyl)furoin (DHMF).23 Given that ILs are commercially available and offer an inexpensive way of generating NHCs, we were interested in investigating what other types of reactions ILs could perform. To this end, we found that dialkyl imidazoliums could efficiently be used as precatalysts in the formal conjugate addition of unsaturated aldehydes to chalcones (Figure 1) giving 1,6-ketoesters. The most efficient IL, EMIMAc, promotes a highly stereoselective reaction between cinnamaldehyde and chalcone. The reaction occurs with high preference for the anti-diastereomer and the 1,6-ketoesters can be isolated in yields up to 92%.24,25,26
<img alt="Figure 1" src="/files/ftp_upload/53213/53213fig1.jpg" /> 
Figure 1: IL-mediated three-component, stereoselective addition of cinnamaldehyde to chalcone.

<table>
	<tbody>
		<tr>
			<td>1-ethyl-3-methyl imidazolium acetate</td>
			<td>Aldrich</td>
			<td>51053-100G-F</td>
			<td>Produced by BASF &#8805;90%, dried on a rotary evaporated before use (10 mBar, 40 &#176;C, 1h) 
			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% 
			CAS NUMBER: 94-41-7</td>
		</tr>
		<tr>
			<td>trans-cinnamaldehyde&#160;</td>
			<td>Aldrich</td>
			<td>C80687-25G</td>
			<td>99%, stored under nitrogen prior to use 
			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% 
			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. &#8805;99.8% (GC) 
			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 
			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 
			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.

As exemplified above, EMIMAc serve as a precatalyst in the formal conjugate addition of &#945;,&#946;-unsaturated aldehyde to chalcones. Other commercially available imidazolium based ILs such as 1-ethyl-3-methylimidazolium chloride (EMIMCl) and 1-butyl-3-methylimidazolium chloride (BMIMCl) were also investigated, however, these reactions proceeded in lower yields indicating that the acetate anion may be important for reactivity (Table 1, entry 1-3).27,28*
<p class="jove_c...

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.

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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