Catalytic Diels Research Articles

Catalytic Diels–Alder Reaction of α,β-Unsaturated Methyl Esters

Catalytic Diels–Alder Reaction of α,β-Unsaturated Methyl Esters

Scalable and Highly Diastereo- and Enantioselective Catalytic Diels-Alder Reaction of α,β-Unsaturated Methyl Esters.

Despite tremendous advances in enantioselective catalysis of the Diels-Alder reaction, the use of simple α,β-unsaturated esters, one of the most abundant and useful class of dienophiles, is still severely limited in scope due to their low reactivity. We report here a catalytic asymmetric Diels-Alder methodology for a large variety of α,β-unsaturated methyl esters and different dienes based on extremely reactive silylium imidodiphosphorimidate (IDPi) Lewis acids. Mechanistic insights from accurate domain-based local pair natural orbital coupled-cluster (DLPNO-CCSD(T)) calculations rationalize the catalyst control and stereochemical outcome.

Janus Face of the Steric Effect in a Lewis Acid Catalyst with Size-Exclusion Design: Steric Repulsion and Steric Attraction in the Catalytic Exo-Selective Diels–Alder Reaction

An exo-selective catalytic Diels–Alder reaction was developed using a Lewis acid catalyst with size-exclusion structural design. Exploiting the steric effect, especially the steric attraction, the Lewis acid catalyst was able to reroute the reaction along a higher-energy pathway. The experimental findings were also supported by theoretical calculations. This catalyst development allows an easy and practical access to highly complex and pharmaceutically relevant compounds.

Multi-site Cooperativity in Alkali-Metal-Exchanged Faujasites for the Production of Biomass-Derived Aromatics.

The catalytic Diels–Alder cycloaddition–dehydration (DACD) reaction of furanics with ethylene is a promising route to bio‐derived aromatics. The reaction can be catalyzed by alkali‐metal‐exchanged faujasites. Herein, the results of periodic DFT calculations based on accurate structural models of alkali‐metal‐exchanged zeolites are presented, revealing the fundamental roles that confinement and the nature of the exchangeable cations in zeolite micropores have in the performance of faujasite‐based catalysts in the DACd reaction. Special attention is devoted to analyzing the effect of functional substituents on furanic substrates (furan, 2,5‐dimethylfuran, 2,5‐furandicarboxylic acid) on the catalyst behavior. It is demonstrated that the conventional reactivity theories of the Diels–Alder chemistry based on simplistic single‐site Lewis acidity and substituent effects do not apply if catalytic processes in the multiple‐site confined environment of zeolite nanopores are considered. The nature and cooperativity of the interactions between the multiple exchangeable cations and the substrates determine the reaction energetics of the elementary steps involved in the DACD process.

Pursuing the active species in an aluminium-based Lewis acid system for catalytic Diels–Alder cycloadditions

Several Al-based complexes supported by a bis(imino)aryl NCN pincer ligand have been prepared. Systematic structural and experimental evidence identified a cationic species, supported by a THF molecule, as the best Lewis acid precatalyst for a range of Diels-Alder cycloadditions. This highlighted the importance of fully isolating and characterizing the active species in any catalytic process especially when Lewis acids are used due to the presence of hidden Brønsted acids (HBAs). Finally, the control experiments conducted in order to eliminate HBA activity that involve a bulky pyridine base should be performed with caution as the corresponding protonated pyridinium salt could also serve as a proton source.

Correction to Enantioselective Catalytic Diels–Alder Reactions with Enones As Dienophiles

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to Enantioselective Catalytic Diels–Alder Reactions with Enones As DienophilesDaniel Carmona*, Fernando Viguri*, Ainara Asenjo, Fernando J. Lahoz, Pilar Garcı́a-Orduña, and Luis A. OroCite this: Organometallics 2016, 35, 9, 1339Publication Date (Web):April 27, 2016Publication History Published online27 April 2016Published inissue 9 May 2016https://doi.org/10.1021/acs.organomet.6b00319Copyright © 2016 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views512Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (102 KB) Get e-Alerts Get e-Alerts

Stereoselective synthesis of chiral hydrocarbazoles via the catalytic Diels–Alder reaction of siloxyvinylindole and cyclic Z-olefin

The catalytic Diels–Alder reaction of siloxyvinylindole and cyclic Z-olefin derived from pyroglutamic acid gave optically active substituted hydrocarbazoles. The exo/endo selectivity of this reaction could be controlled by using an appropriate Lewis acid. Scandium triflate gave high exo-selectivity and copper triflate gave moderate endo-selectivity. Subsequent stereoselective alkylation of the cycloadduct led to the synthesis of highly substituted hydrocarbazoles with five continuous chiral centers including a quaternary carbon.

ChemInform Abstract: Construction of Chiral Bridged Tricyclic Benzopyrans: Enantioselective Catalytic Diels—Alder Reaction and a One‐Pot Reduction/Acid‐Catalyzed Stereoselective Cyclization.

An asymmetric two-step approach to chiral bridged tricyclic benzopyrans, core structures featured in various natural products, is described. In the synthesis, an unprecedented enantioselective catalytic decarboxylative Diels–Alder reaction is developed using readily available coumarin-3-carboxylic acids and aldehydes as reactants under mild reaction conditions. Notably, the decarboxylation-assisted release of the catalyst enables the process to proceed efficiently with high enantio- and diastereoselectivity. Furthermore, a one-pot procedure for either a LiAlH4- or NaBH4-mediated reduction with subsequent acid-catalyzed intramolecular cyclization of the Diels–Alder adducts was identified for the efficient formation of the chiral bridged tricyclic benzopyrans.

Construction of Chiral Bridged Tricyclic Benzopyrans: Enantioselective Catalytic Diels–Alder Reaction and a One‐Pot Reduction/Acid‐Catalyzed Stereoselective Cyclization

An asymmetric two-step approach to chiral bridged tricyclic benzopyrans, core structures featured in various natural products, is described. In the synthesis, an unprecedented enantioselective catalytic decarboxylative Diels-Alder reaction is developed using readily available coumarin-3-carboxylic acids and aldehydes as reactants under mild reaction conditions. Notably, the decarboxylation-assisted release of the catalyst enables the process to proceed efficiently with high enantio- and diastereoselectivity. Furthermore, a one-pot procedure for either a LiAlH4 - or NaBH4 -mediated reduction with subsequent acid-catalyzed intramolecular cyclization of the Diels-Alder adducts was identified for the efficient formation of the chiral bridged tricyclic benzopyrans.

Construction of Chiral Bridged Tricyclic Benzopyrans: Enantioselective Catalytic Diels–Alder Reaction and a One‐Pot Reduction/Acid‐Catalyzed Stereoselective Cyclization

AbstractAn asymmetric two‐step approach to chiral bridged tricyclic benzopyrans, core structures featured in various natural products, is described. In the synthesis, an unprecedented enantioselective catalytic decarboxylative Diels–Alder reaction is developed using readily available coumarin‐3‐carboxylic acids and aldehydes as reactants under mild reaction conditions. Notably, the decarboxylation‐assisted release of the catalyst enables the process to proceed efficiently with high enantio‐ and diastereoselectivity. Furthermore, a one‐pot procedure for either a LiAlH4‐ or NaBH4‐mediated reduction with subsequent acid‐catalyzed intramolecular cyclization of the Diels–Alder adducts was identified for the efficient formation of the chiral bridged tricyclic benzopyrans.

Stereoselectivity through a network of non-classical CH weak interactions: a prospective study of a bicyclic organocatalytic scaffold

The preferred stereoisomeric product of this catalytic Diels–Alder reaction is in part determined by noncovalent CH⋯π interactions.

Enantioselective Catalytic Diels–Alder Reactions with Enones As Dienophiles

The aqua complexes (SM,RC)-[(η5-C5Me5)M(PROPHOS)(H2O)][SbF6]2 [PROPHOS = (R)-propane-1,2-diylbis(diphenylphosphane); M = Rh (1), Ir (2)] are active catalysts for the asymmetric Diels–Alder reaction between ketones and dienes. At low temperatures, enantioselectivities of up to 89% ee are achieved. The intermediate Lewis acid–dienophile complexes (SM,RC)-[(η5-C5Me5)M(PROPHOS)(MVK)][SbF6]2 (MVK = methyl vinyl ketone; M = Rh (3), Ir (4)) and (SIr,RC)-[(η5-C5Me5)Ir(PROPHOS)(EVK)][SbF6]2 (EVK = ethyl vinyl ketone (5)) have been isolated and characterized by analytical and spectroscopic means, including the determination of the crystal structure of the iridium complexes 4 and 5 by X-ray diffractometric methods. Structural parameters indicate that the dispositions of the coordinated dienophiles are controlled by the CH/π attractive interactions established between a phenyl group of the PROPHOS ligand and the α-vinyl proton of the ketones. Proton NMR parameters indicate that these interactions are maintained in so...

Micellar-driven substrate selectivity in Cr(salen)Cl catalytic Diels–Alder reaction in water

A 3.5 increase in catalytic activity was observed in the Cr(III) (salen)Cl 3 catalyzed Diels–Alder reaction between cyclopentadiene 1 with the longer trans-2-decenal 2g compared to the shorter trans-2-butenal 2a dienophile under aqueous micellar conditions, while in chloroform the two substrates react with comparable activities.

ChemInform Abstract: A New Class of Enantioselective Catalytic 2‐Pyrone Diels—Alder Cycloadditions.

A highly enantioselective catalytic Diels- Alder (DA) cycloaddition of 2H-pyran-2,5-diones (synthon of 5-hydroxy-2-pyrones) has been devel- oped with a Cinchona-derived thiourea as the cata- lyst. The conditions were optimized by using 0.2 equiv. of the catalyst and 0.1 equiv. of formic acid in 2-propanol at room temperature, which afforded the DA products in yields of up to 90% (exo/endo = 5.5:1, 98% ee) with trans-b-nitrostyrene derivatives as the dienophiles. The structure/activity relation- ships of the bifunctional catalyst and the effects of the steric, electronic and hydrogen-bonding proper- ties of the dienophiles have been studied.

A New Class of Enantioselective Catalytic 2‐Pyrone Diels–Alder Cycloadditions

AbstractA highly enantioselective catalytic Diels–Alder (DA) cycloaddition of 2H‐pyran‐2,5‐diones (synthon of 5‐hydroxy‐2‐pyrones) has been developed with a Cinchona‐derived thiourea as the catalyst. The conditions were optimized by using 0.2 equiv. of the catalyst and 0.1 equiv. of formic acid in 2‐propanol at room temperature, which afforded the DA products in yields of up to 90% (exo/endo=5.5:1, 98% ee) with trans‐β‐nitrostyrene derivatives as the dienophiles. The structure/activity relationships of the bifunctional catalyst and the effects of the steric, electronic and hydrogen‐bonding properties of the dienophiles have been studied.

Aluminium complexes derived from tridentate thioetherbis(phenolate) ligands and their activity in Diels–Alder catalysis

Organoaluminium(III) thioetherbis(phenolate) complexes derived from 2,2-thiobis(4,6-diterbuthylphenolate) (Stdiol) and 2,2-thiobis(4,6-dimethylphenolate) (Smdiol) were prepared by reaction of AlMe3 with the diol proligands LH2 (SmdiolH2, StdiolH2). Monomeric complexes of general formulae [LAlR(L)] (L = Stdiol, R = Me, L = THF (1); L = Stdiol, R = Me, L = Et2O (2); L = Stdiol, R = iBu, L = THF) (3); L = Smdiol, R = Me, L = THF (4); L = Smdiol, R = iBu, L = THF (5)) and [LAlCl(THF)] (L = Stdiol (6); L = Smdiol (7)) were obtained when the reactions were performed in THF or Et2O in hexane or toluene, species of formulae [(L2Al)AlR2] (L = Stdiol, R = Me (8); L = Stdiol, R = iBu (9); L = Smdiol, R = Me (10)) were formed as evidenced by spectroscopic methods. Crystals suitable for X-ray diffraction studies were obtained for 2, 3, 4, 6, 8, 9 and 10. In these cases the sulfur atom coordinates to the aluminium center with Al-S bond lengths between 2.43-2.75 A adopting boat-boat conformations. Compounds 1, 3, 4, and 8 were tested in the catalytic Diels-Alder cycloaddition reaction between methacrolein and cyclopentadiene showing excellent regioselectivities with good conversion yields.

Closely related antibody receptors exploit fundamentally different strategies for steroid recognition

Molecular recognition by the adaptive immune system relies on specific high-affinity antibody receptors that are generated from a restricted set of starting sequences through homologous recombination and somatic mutation. The steroid binding antibody DB3 and the catalytic Diels-Alderase antibody 1E9 derive from the same germ line sequences but exhibit very distinct specificities and functions. However, mutation of only two of the 36 sequence differences in the variable domains, Leu(H47)Trp and Arg(H100)Trp, converts 1E9 into a high-affinity steroid receptor with a ligand recognition profile similar to DB3. To understand how these changes switch binding specificity and function, we determined the crystal structures of the 1E9 Leu(H47)Trp/Arg(H100)Trp double mutant (1E9dm) as an unliganded Fab at 2.05 A resolution and in complex with two configurationally distinct steroids at 2.40 and 2.85 A. Surprisingly, despite the functional mimicry of DB3, 1E9dm employs a distinct steroid binding mechanism. Extensive structural rearrangements occur in the combining site, where residue H47 acts as a specificity switch and H100 adapts to different ligands. Unlike DB3, 1E9dm does not use alternative binding pockets or different sets of hydrogen-bonding interactions to bind configurationally distinct steroids. Rather, the different steroids are inserted more deeply into the 1E9dm combining site, creating more hydrophobic contacts that energetically compensate for the lack of hydrogen bonds. These findings demonstrate how subtle mutations within an existing molecular scaffold can dramatically modulate the function of immune receptors by inducing unanticipated, but compensating, mechanisms of ligand interaction.

Asymmetric Diels−Alder Reactions of 2-Pyrones with a Bifunctional Organic Catalyst

The reactions of 2-pyrones with electron-deficient dienophiles constitute a synthetically useful class of Diels−Alder reaction. By exploring cinchona alkaloid-derived organic molecules as acid−base bifunctional catalysts, we successfully developed the first highly enantioselective and diastereoselective catalytic Diels−Alder reaction with 2-pyrones. Furthermore, we demonstrated the possibility of using such catalysts to control the endo/exo selectivity in a Diels−Alder reaction.

An Examination of VANOL, VAPOL, and VAPOL Derivatives as Ligands for Asymmetric Catalytic Diels—Alder Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Development of effective Lewis acids for the catalytic Diels–Alder reaction of α,β-unsaturated lactones with cyclopentadiene

We found that ‘Tf 2CH 2 + Me 3Al’ systems are effective catalytic systems for the DA reaction of less reactive α,β-unsaturated lactone derivatives, compared to α,β-unsaturated ester derivatives, with cyclopentadiene. Mononuclear aluminum methide complex, Tf 2CHAlMe 2, as an active species is formed in these catalytic systems. Effects of lactone ring-size on the reactivity and stereoselectivity were also examined. By expanding ring-size, reactivity of α,β-unsaturated lactones reduced but endo-selectivity notably increased.