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Huang GT, Yu JSK. Catalytic role of the enol ether intermediate in the intramolecular Stetter reaction: a computational perspective. Phys Chem Chem Phys 2024; 26:11833-11853. [PMID: 38567403 DOI: 10.1039/d3cp06051a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
The intramolecular Stetter reaction catalyzed by a carbene is investigated by density functional theory (DFT) calculations and kinetic simulations. Catalyst 1 first reacts with aldehyde 2 to give the primary adduct (PA). The PA undergoes the intramolecular oxa-Michael reaction to irreversibly generate enol ether intermediate 9. The conversion of the enol ether to the Breslow intermediate (BI) requires the assistance of a base such as the PA. The next step involves formation of a carbon-carbon bond through the Michael addition, and expulsion of the catalyst generates the Stetter product 7. Calculations show that the catalytic cycle is composed of two irreversible processes: the first one involves the exergonic formation of the enol ether intermediate, while the second one is the conversion of the enol ether to the final product. Kinetic simulations using initial concentrations of [1]0 = 0.005 M and [2]0 = 0.025 M demonstrate that under a steady-state condition, 35% of the catalyst rests on the state of the enol ether (0.0018 M). The catalyst resting state therefore consists of the unbound form (the free catalyst) and its bound form (the enol ether species). According to variable time normalization analysis, the reaction exhibits a second-order dependence (first order in catalyst and first order in substrate), which agrees with experiments. The oxa-Michael reaction to form the enol ether is identified to be turnover limiting in the intramolecular Stetter reaction, which rationalizes the observed electronic effect of the Michael acceptor on the reactivity, as well as the measured isotope effect with respect to the aldehydic proton/deuteron. The base that participates in the BI formation has a significant effect on the build-up of the resting state 9 and the active catalyst concentration. In addition, the thermodynamic stability of the enol ether is found to depend on the tether length between the aromatic aldehyde and the Michael acceptor, as well as the chemical nature of the carbene catalyst. The favorability for the oxa-Michael reaction is therefore suggested to govern the reactivity of the intramolecular Stetter transformation.
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Affiliation(s)
- Gou-Tao Huang
- Department of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsinchu City 300, Taiwan.
| | - Jen-Shiang K Yu
- Department of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsinchu City 300, Taiwan.
- Institute of Bioinformatics and Systems Biology, National Yang Ming Chiao Tung University, Hsinchu City 300, Taiwan
- Center for Intelligent Drug Systems and Smart Bio-devices (IDS2B), National Yang Ming Chiao Tung University, Hsinchu City 300, Taiwan
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2
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Rummel L, Schreiner PR. Advances and Prospects in Understanding London Dispersion Interactions in Molecular Chemistry. Angew Chem Int Ed Engl 2024; 63:e202316364. [PMID: 38051426 DOI: 10.1002/anie.202316364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2023] [Revised: 12/03/2023] [Accepted: 12/05/2023] [Indexed: 12/07/2023]
Abstract
London dispersion (LD) interactions are the main contribution of the attractive part of the van der Waals potential. Even though LD effects are the driving force for molecular aggregation and recognition, the role of these omnipresent interactions in structure and reactivity had been largely underappreciated over decades. However, in the recent years considerable efforts have been made to thoroughly study LD interactions and their potential as a chemical design element for structures and catalysis. This was made possible through a fruitful interplay of theory and experiment. This review highlights recent results and advances in utilizing LD interactions as a structural motif to understand and utilize intra- and intermolecularly LD-stabilized systems. Additionally, we focus on the quantification of LD interactions and their fundamental role in chemical reactions.
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Affiliation(s)
- Lars Rummel
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392, Giessen, Germany
| | - Peter R Schreiner
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392, Giessen, Germany
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3
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Nakano Y, Maddigan-Wyatt JT, Lupton DW. Enantioselective Catalysis by the Umpolung of Conjugate Acceptors Involving N-Heterocyclic Carbene or Organophosphine 1,4-Addition. Acc Chem Res 2023; 56:1190-1203. [PMID: 37093247 DOI: 10.1021/acs.accounts.3c00063] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2023]
Abstract
ConspectusConjugate acceptors are one of the most common electrophilic functional groups in organic synthesis. While useful in a diverse range of transformations, their applications are largely dominated by the reactions from which their name is derived (i.e., as an acceptor of nucleophiles in the conjugate position). In 2014, we commenced studies focused on their ability to undergo polarity inversion through the conjugate addition of Lewis base catalysts. The first step in this process provides an enolate, from which the well-developed Rauhut-Currier (RC) and Morita-Baylis-Hillman (MBH) reactions can occur; however, tautomerization to provide a species in which the β-carbon of the conjugate acceptor can now act as a donor is also possible. When we commenced studies on this topic, reaction designs with this type of species, particularly when accessed using N-heterocyclic carbenes (NHCs), had been reported on only a handful of occasions. Despite a lack of development, conceptually it was felt that reactions taking advantage of polarity switching by Lewis base conjugate addition have a number of desirable features. Perhaps the most significant is the potential to reimagine a ubiquitous functional group as an entirely new synthon, namely, a donor to electrophiles from the conjugate position.Our work has focused on catalysis with both simple conjugate acceptors and also those embedded within more complicated substrates; the latter has allowed a series of cycloisomerizations and annulation reactions to be achieved. In most cases, the reactions have been possible using enantioenriched chiral NHCs or organophosphines as the Lewis base catalysts thereby delivering enantioselective approaches to novel cyclic molecules. While related chemistry can be accessed with either family of catalyst, in all cases reactions have been designed to take advantage of one or the other. In addition, a fine balance exists between reactions that exploit the initially formed enolate and those that involve the polarity-inverted β-anion. In our studies, this balance is addressed through substrate design, although catalyst control may also be possible. We consider the chemistry discussed in this Account to be in its infancy. Significant challenges remain to be addressed before our broad aim of discovering a universal approach to the polarity inversion of all conjugate acceptors can be achieved. These challenges broadly relate to chemoselectivity with substrates bearing multiple electrophilic functionalities, reliance upon the use of conjugate acceptors, and catalyst efficiency. To address these challenges, advances in catalyst design and catalyst cooperativity are likely required.
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Affiliation(s)
- Yuji Nakano
- School of Chemistry, Monash University, Clayton 3800, Victoria, Australia
| | | | - David W Lupton
- School of Chemistry, Monash University, Clayton 3800, Victoria, Australia
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4
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Abstract
Oxidative carbene organocatalysis, which proceeds via single electron transfer (SET) pathways, has been limited by the moderately reducing properties of deprotonated Breslow intermediates BI-s derived from thiazol-2-ylidene 1 and 1,2,4-triazolylidene 2. Using computational methods, we assess the redox potentials of BI-s based on ten different types of known stable carbenes and report our findings concerning the key parameters influencing the steps of the catalytic cycle. From the calculated values of the first oxidation potential of BI-s derived from carbenes 1 to 10, it appears that, apart from the diamidocarbene 7, all the others are more reducing than thiazol-2-ylidene 1 and the 1,2,4-triazolylidene 2. We observed that while the reducing power of BI-s significantly decreases with increasing solvent polarity, the redox potential of the oxidant can increase at a greater rate, thus facilitating the reaction. The cation, associated with the base, also plays an important role when a nonpolar solvent is used; large and weakly coordinating cations such as Cs+ are beneficial. The radical-radical coupling step is probably the most challenging step due to both electronic and steric constraints. Based on our results, we predict that mesoionic carbene 3 and abnormal NHC 4 are the most promising candidates for oxidative carbene organocatalysis.
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Affiliation(s)
- Florian F Mulks
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea.,Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.,UCSD-CNRS Joint Research Chemistry Laboratory (UMI 3555), Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0358, United States
| | - Mohand Melaimi
- UCSD-CNRS Joint Research Chemistry Laboratory (UMI 3555), Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0358, United States
| | - Xiaoyu Yan
- Department of Chemistry, Renmin University of China, Beijing 100872, People's Republic of China
| | - Mu-Hyun Baik
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea.,Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Guy Bertrand
- UCSD-CNRS Joint Research Chemistry Laboratory (UMI 3555), Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0358, United States
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5
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Dubey G, Singh T, Bharatam PV. The importance of four-membered NHCs in stabilizing Breslow intermediates on benzoin condensation pathway. J Comput Chem 2023; 44:346-354. [PMID: 35652523 DOI: 10.1002/jcc.26935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Revised: 04/27/2022] [Accepted: 05/07/2022] [Indexed: 01/03/2023]
Abstract
N-heterocyclic carbenes (NHCs) have been established to be effective organocatalysts for facilitating the benzoin condensation and many other reactions. These reactions involve the formation of a Breslow intermediate (BI), which exhibits umpolung chemistry. To facilitate organocatalysis, several new cyclic carbenes are being introduced, four-membered NHCs are of special interest. Whether these NHCs can exhibit catalytic influence or not, can be evaluated by exploring the potential energy surface (PES) of the benzoin condensation reaction. Quantum chemical analysis has been carried out to compare the PES of these four-membered NHCs with that of standard five-membered NHCs to explore their catalytic ability. The barrier for the first step of the reaction for the formation of BI is comparable in all the cases. But the barrier for the second step of the reaction leading to the benzoin formation from BI is estimated to be very high for the four membered NHCs. These results indicate that the probability of identifying and isolating the BI is very high in comparison to the completion of benzoin condensation reaction in the case of the four-membered NHCs.
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Affiliation(s)
- Gurudutt Dubey
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), SAS Nagar, India
| | - Tejender Singh
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), SAS Nagar, India
| | - Prasad V Bharatam
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), SAS Nagar, India
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6
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Abstract
N-Heterocyclic carbene (NHC) catalysis is a by now consolidated organocatalytic platform for a number of synthetic (asymmetric) transformations via diverse reaction modes/intermediates. In addition to the typical umpolung processes involving acyl anion/homoenolate equivalent species, implementation of protocols under oxidative conditions greatly expands the possibilities of this methodology. Oxidative NHC-catalysis allows for oxidative and oxygenative transformations through specific manipulations of Breslow-type species depending upon the oxidant used (external oxidant or O2 /air), the derived NHC-bound intermediates paving the way to non-umpolung processes through activation of carbon atoms and heteroatoms. This review is intended to update the state of the art in oxidative NHC-catalyzed reactions that appeared in the literature from 2014 to present, with a strong focus to crucial intermediates and their mechanistic implications.
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Affiliation(s)
- Carmela De Risi
- Dipartimento di Scienze Chimiche, Farmaceutiche ed Agrarie, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Arianna Brandolese
- Dipartimento di Scienze dell'Ambiente e della Prevenzione, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Graziano Di Carmine
- Dipartimento di Scienze Chimiche, Farmaceutiche ed Agrarie, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Daniele Ragno
- Dipartimento di Scienze Chimiche, Farmaceutiche ed Agrarie, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Alessandro Massi
- Dipartimento di Scienze Chimiche, Farmaceutiche ed Agrarie, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Olga Bortolini
- Dipartimento di Scienze dell'Ambiente e della Prevenzione, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
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7
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Peltier JL, Serrato MR, Thery V, Pecaut J, Tomás-Mendivil E, Bertrand G, Jazzar R, Martin D. An air-stable radical with a redox-chameleonic amide. Chem Commun (Camb) 2023; 59:595-598. [PMID: 36524847 DOI: 10.1039/d2cc05404c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
An air-stable (amino)(amido)radical was synthesized by reacting a cyclic (alkyl)(amino)carbene with carbazoyl chloride, followed by one-electron reduction. We show that an adjacent radical center weakens the amide bond. It enables the amino group to act as a strong acceptor under steric contraint, thus enhancing the stabilizing capto-dative effect.
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Affiliation(s)
- Jesse L Peltier
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093-0358, USA
| | - Melinda R Serrato
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093-0358, USA
| | - Valentin Thery
- University Grenoble Alpes, CNRS, DCM, Grenoble 38000, France.
| | - Jacques Pecaut
- University Grenoble Alpes, CEA, CNRS, INAC-SyMMES, UMR 5819, Grenoble 38000, France
| | | | - Guy Bertrand
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093-0358, USA
| | - Rodolphe Jazzar
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093-0358, USA
| | - David Martin
- University Grenoble Alpes, CNRS, DCM, Grenoble 38000, France.
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8
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Duan Z, Young CM, Zhu J, Slawin AMZ, O'Donoghue AC, Smith AD. Rate and equilibrium constants for the addition of triazolium salt derived N-heterocyclic carbenes to heteroaromatic aldehydes. Chem Sci 2022; 14:162-170. [PMID: 36605738 PMCID: PMC9769090 DOI: 10.1039/d2sc05704b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 11/13/2022] [Indexed: 11/16/2022] Open
Abstract
Heteroaromatic aldehydes are often used preferentially or exclusively in a range of NHC-catalysed processes that proceed through the generation of a reactive diaminoenol or Breslow Intermediate (BI), with the reason for their unique reactivity currently underexplored. This manuscript reports measurement of rate and equilibrium constants for the reaction between N-aryl triazolium NHCs and heteroaromatic aldehydes, providing insight into the effect of the NHC and heteroaromatic aldehyde structure up to formation of the BI. Variation in NHC catalyst and heteroaromatic aldehyde structure markedly affect the observed kinetic parameters of adduct formation, decay to starting materials and onward reaction to BI. In particular, large effects are observed with both 3-halogen (Br, F) and 3-methyl substituted pyridine-2-carboxaldehyde derivatives which substantially favour formation of the tetrahedral intermediate relative to benzaldehyde derivatives. Key observations indicate that increased steric hindrance leads to a reduction in both k 2 and k -1 for large (2,6-disubstituted)-N-Ar groups within the triazolium scaffold, and sterically demanding aldehyde substituents in the 3-position, but not in the 6-position of the pyridine-2-carboxaldehyde derivatives. As part of this study, the isolation and characterisation of twenty tetrahedral adducts formed upon addition of N-aryl triazolium derived NHCs into heteroaromatic aldehydes are described. These adducts are key intermediates in NHC-catalysed umpolung addition of heteroaromatic aldehydes and are BI precursors.
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Affiliation(s)
- Zhuan Duan
- EaStCHEM, School of Chemistry, University of St AndrewsNorth HaughSt AndrewsFifeKY16 9STUK
| | - Claire M. Young
- EaStCHEM, School of Chemistry, University of St AndrewsNorth HaughSt AndrewsFifeKY16 9STUK
| | - Jiayun Zhu
- Department of Chemistry, Durham UniversitySouth RoadDurham DH1 3LEUK
| | - Alexandra M. Z. Slawin
- EaStCHEM, School of Chemistry, University of St AndrewsNorth HaughSt AndrewsFifeKY16 9STUK
| | | | - Andrew D. Smith
- EaStCHEM, School of Chemistry, University of St AndrewsNorth HaughSt AndrewsFifeKY16 9STUK
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9
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Rowshanpour R, Gravel M, Dudding T. N-Heterocyclic Carbene Organocatalyzed Redox-Active/Ring Expansion Reactions: Mechanistic Insights Unveiling Base Cooperativity. J Org Chem 2022; 87:16785-16793. [DOI: 10.1021/acs.joc.2c02462] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Affiliation(s)
- Rozhin Rowshanpour
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S3A1, Canada
| | - Michel Gravel
- Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N5C9, Canada
| | - Travis Dudding
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S3A1, Canada
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10
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Du HW, Liu MS, Shu W. Synthesis of β-Thiolated-α-arylated Ketones Enabled by Photoredox and N-Heterocyclic Carbene-Catalyzed Radical Relay of Alkenes with Disulfides and Aldehydes. Org Lett 2022; 24:5519-5524. [PMID: 35862874 DOI: 10.1021/acs.orglett.2c01915] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
β-Thiolated-α-arylated ketones are perversive in bioactive molecules and serve as potential bidentate ligands for catalysis. Herein, a straightforward protocol to access β-thiolated ketones from aldehydes, alkenes, and disulfides enabled by the combination of photocatalysis and N-heterocyclic carbene catalysis is reported. The sequential radical addition to alkenes and subsequent radical-radical coupling cascade process simultaneously forge C-S and C-C bonds. The mild conditions allow for radical relay coupling with a broad functional group tolerance.
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Affiliation(s)
- Hai-Wu Du
- Shenzhen Grubbs Institute, Department of Chemistry, and Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen, Guangdong 518055, P. R. China
| | - Ming-Shang Liu
- Shenzhen Grubbs Institute, Department of Chemistry, and Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen, Guangdong 518055, P. R. China
| | - Wei Shu
- Shenzhen Grubbs Institute, Department of Chemistry, and Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen, Guangdong 518055, P. R. China
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11
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Wessels A, Klussmann M, Breugst M, Schlörer NE, Berkessel A. Formation of Breslow Intermediates from N‐Heterocyclic Carbenes and Aldehydes Involves Autocatalysis by the Breslow Intermediate, and a Hemiacetal. Angew Chem Int Ed Engl 2022; 61:e202117682. [PMID: 35238462 PMCID: PMC9325009 DOI: 10.1002/anie.202117682] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Indexed: 11/23/2022]
Abstract
Under aprotic conditions, the stoichiometric reaction of N‐heterocyclic carbenes (NHCs) such as imidazolidin‐2‐ylidenes with aldehydes affords Breslow Intermediates (BIs), involving a formal 1,2‐C‐to‐O proton shift. We herein report kinetic studies (NMR), complemented by DFT calculations, on the mechanism of this kinetically disfavored H‐translocation. Variable time normalization analysis (VTNA) revealed that the kinetic orders of the reactants vary for different NHC‐to‐aldehyde ratios, indicating different and ratio‐dependent mechanistic regimes. We propose that for high NHC‐to‐aldehyde ratios, the H‐shift takes place in the primary, zwitterionic NHC‐aldehyde adduct. With excess aldehyde, the zwitterion is in equilibrium with a hemiacetal, in which the H‐shift occurs. In both regimes, the critical H‐shift is auto‐catalyzed by the BI. Kinetic isotope effects observed for R‐CDO are in line with our proposal. Furthermore, we detected an H‐bonded complex of the BI with excess NHC (NMR).
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Affiliation(s)
- Alina Wessels
- Department of Chemistry Organic Chemistry University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Martin Klussmann
- Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1 45470 Mülheim an der Ruhr Germany
- Borchers GmbH Berghausener Straße 100 40764 Langenfeld Germany
| | - Martin Breugst
- Department of Chemistry Organic Chemistry University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Nils E. Schlörer
- Department of Chemistry Organic Chemistry University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Albrecht Berkessel
- Department of Chemistry Organic Chemistry University of Cologne Greinstraße 4 50939 Cologne Germany
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12
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Machín Rivera R, Burton NR, Call LD, Tomat MA, Lindsay VNG. Synthesis of Highly Congested Tertiary Alcohols via the [3,3] Radical Deconstruction of Breslow Intermediates. Org Lett 2022; 24:4275-4280. [PMID: 35657720 DOI: 10.1021/acs.orglett.2c01627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Pericyclic processes such as [3,3]-sigmatropic rearrangements leading to the rapid generation of molecular complexity constitute highly valuable tools in organic synthesis. Herein, we report the formation of particularly hindered tertiary alcohols via rearrangement of Breslow intermediates formed in situ from readily available N-allyl thiazolium salts and benzaldehyde derivatives. Experimental mechanistic studies performed suggest that the reaction proceeds via a close radical pair which recombine in a regio- and diastereoselective manner, formally leading to [3,3]-rearranged products.
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Affiliation(s)
- Roger Machín Rivera
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
| | - Nikolas R Burton
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
| | - Luke D Call
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
| | - Marshall A Tomat
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
| | - Vincent N G Lindsay
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
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13
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Zhang J, Li T, Li X, Lv A, Li X, Wang Z, Wang R, Ma Y, Fang R, Szostak R, Szostak M. Thiazol-2-ylidenes as N-Heterocyclic carbene ligands with enhanced electrophilicity for transition metal catalysis. Commun Chem 2022; 5:60. [PMID: 36697942 DOI: 10.1038/s42004-022-00675-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Accepted: 04/21/2022] [Indexed: 01/28/2023] Open
Abstract
Over the last 20 years, N-heterocyclic carbenes (NHCs) have emerged as a dominant direction in ligand development in transition metal catalysis. In particular, strong σ-donation in combination with tunable steric environment make NHCs to be among the most common ligands used for C-C and C-heteroatom bond formation. Herein, we report the study on steric and electronic properties of thiazol-2-ylidenes. We demonstrate that the thiazole heterocycle and enhanced π-electrophilicity result in a class of highly active carbene ligands for electrophilic cyclization reactions to form valuable oxazoline heterocycles. The evaluation of steric, electron-donating and π-accepting properties as well as structural characterization and coordination chemistry is presented. This mode of catalysis can be applied to late-stage drug functionalization to furnish attractive building blocks for medicinal chemistry. Considering the key role of N-heterocyclic ligands, we anticipate that N-aryl thiazol-2-ylidenes will be of broad interest as ligands in modern chemical synthesis.
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14
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Wessels A, Klussmann M, Breugst M, Schlörer NE, Berkessel A. Die Bildung von Breslow‐Intermediaten aus N‐heterocyclischen Carbenen und Aldehyden verläuft autokatalytisch und mit einem Halbacetal als Intermediat. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202117682] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Alina Wessels
- Department für Chemie Organische Chemie Universität zu Köln Greinstraße 4 50939 Köln Deutschland
| | - Martin Klussmann
- Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1 45470 Mülheim an der Ruhr Deutschland
- Borchers GmbH Berghausener Straße 100 40764 Langenfeld Deutschland
| | - Martin Breugst
- Department für Chemie Organische Chemie Universität zu Köln Greinstraße 4 50939 Köln Deutschland
| | - Nils E. Schlörer
- Department für Chemie Organische Chemie Universität zu Köln Greinstraße 4 50939 Köln Deutschland
| | - Albrecht Berkessel
- Department für Chemie Organische Chemie Universität zu Köln Greinstraße 4 50939 Köln Deutschland
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15
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Wu N, Kluger R. Rates of competing fluoride elimination and iodination from a thiamin-derived Breslow intermediate. Bioorg Chem 2022; 120:105579. [DOI: 10.1016/j.bioorg.2021.105579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 12/09/2021] [Accepted: 12/17/2021] [Indexed: 11/02/2022]
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16
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Abstract
The mechanism of formation of the Breslow intermediate (BI) under aprotic conditions is investigated with density functional theory (DFT) calculations. The zwitterionic adduct (ZA) is formed by the first addition of an imidazolinylidene to benzaldehyde. The forward reaction is found to proceed through the second addition of the ZA to another benzaldehyde, and subsequent proton migration gives a hemiacetal. The bimolecular reaction enables the conversion of the ZA to a more reactive hemiacetal, which is further decomposed to the BI with the assistance of the ZA. During the ZA-assisted process, the hemiacetal and the BI act as hydrogen bond donors to stabilize the ZA. The hydrogen bond interactions between the ZA and the BI or hemiacetal are analyzed. The DFT computations demonstrate that along the proposed route, the proton migration leading to the hemiacetal intermediate is the rate-determining step (ΔG⧧ = 21.2 kcal mol-1). The bimolecular mechanism provides an alternative pathway to explain BI formation under aprotic conditions.
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17
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Hsieh MH, Yu JSK. Fragmentation and rearrangement of Breslow intermediates: branches to both radical and ionic pathways. Phys Chem Chem Phys 2021; 23:27377-27384. [PMID: 34854852 DOI: 10.1039/d1cp03118j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Breslow intermediates are the key species in N-heterocyclic carbene-catalyzed reactions to promote the C-C bond formation. As the fragmentation and rearrangement of Breslow intermediates terminate the catalytic cycle of N-heterocyclic carbene, two mechanisms under debate have been proposed in terms of the radical channel and the ionic route. Theoretical calculations demonstrate herein that ionic and radical characteristics can coexist, depending on the protonation state of the hydroxyl group in Breslow intermediates: radicals are merely generated in the enol system, while both ionic and radical species exist in the enolate system with a lower barrier. Complete pathways for thiamin analogue and N-allyl benzothiazole Breslow intermediates are exclusively constructed considering experimental conditions. The growing population of the enolate under higher pH values rationalizes the increased rate of the fragmentation of thiamin. The fragmentation products of thiamin, namely pyrimidine and ketone, are the thermodynamic products, while the tertiary alcohol is both the kinetic and thermodynamic product for N-allyl benzothiazole Breslow intermediate via a Claisen-like rearrangement. Other NHCs used to synthesize tertiary alcohols could form the enolate due to the base, followed by the production of stable radicals and recombination to form tertiary alcohols. It is concluded that specific protonation states and chemical structures of NHCs account for the distinct mechanisms.
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Affiliation(s)
- Ming-Hsiu Hsieh
- Institute of Bioinformatics and Systems Biology, National Yang Ming Chiao Tung University, No. 75, Bo'ai St., Hsinchu 300, Taiwan
| | - Jen-Shiang K Yu
- Institute of Bioinformatics and Systems Biology, Department of Biological Science and Technology, Institute of Molecular Medicine and Bioengineering, and Center for Intelligent Drug Systems and Smart Bio-devices (IDS2B), National Yang Ming Chiao Tung University, No. 75, Bo'ai St., Hsinchu 300, Taiwan.
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18
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Delfau L, Nichilo S, Molton F, Broggi J, Tomás‐Mendivil E, Martin D. Critical Assessment of the Reducing Ability of Breslow‐type Derivatives and Implications for Carbene‐Catalyzed Radical Reactions**. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202111988] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
| | | | | | - Julie Broggi
- Aix Marseille Univ CNRS Institut de Chimie Radicalaire (ICR) 27 Bd Jean Moulin 13385 Marseille France
| | | | - David Martin
- Univ. Grenoble Alpes CNRS DCM 38000 Grenoble France
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19
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Affiliation(s)
- Ashim Nandi
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Zayed Alassad
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel
| | - Anat Milo
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel
| | - Sebastian Kozuch
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 841051, Israel
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20
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Affiliation(s)
- Ming‐Hsiu Hsieh
- Institute of Bioinformatics and Systems Biology National Yang Ming Chiao Tung University Hsinchu Taiwan
| | - Gou‐Tao Huang
- Department of Biological Science and Technology National Yang Ming Chiao Tung University Hsinchu Taiwan
| | - Jen‐Shiang K. Yu
- Institute of Bioinformatics and Systems Biology, Department of Biological Science and Technology, and Institute of Molecular Medicine and Bioengineering National Yang Ming Chiao Tung University Hsinchu Taiwan
- Center for Intelligent Drug Systems and Smart Bio‐Devices National Yang Ming Chiao Tung University Hsinchu Taiwan
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21
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Delfau L, Nichilo S, Molton F, Broggi J, Tomás-Mendivil E, Martin D. Critical Assessment of the Reducing Ability of Breslow-type Derivatives and Implications for Carbene-Catalyzed Radical Reactions*. Angew Chem Int Ed Engl 2021; 60:26783-26789. [PMID: 34651408 PMCID: PMC9299025 DOI: 10.1002/anie.202111988] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Indexed: 01/05/2023]
Abstract
We report the synthesis of acyl azolium salts stemming from thiazolylidenes CNS, triazolylidenes CTN, mesoionic carbenes CMIC and the generation of their corresponding radicals and enolates, covering about 60 Breslow‐type derivatives. This study highlights the role of additives in the redox behavior of these compounds and unveils several critical misconceptions about radical transformations of aldehyde derivatives under N‐heterocyclic carbene catalysis. In particular, the reducing ability of enolates has been dramatically underestimated in the case of biomimetic CNS. In contrast with previous electrochemical studies, we show that these catalytic intermediates can transfer electrons to iodobenzene within minutes at room temperature. Enols derived from CMIC are not the previously claimed super electron donors, although enolate derivatives of CNS and CMIC are powerful reducing agents.
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Affiliation(s)
| | | | - Florian Molton
- Univ. Grenoble Alpes, CNRS, DCM, 38000, Grenoble, France
| | - Julie Broggi
- Aix Marseille Univ, CNRS, Institut de Chimie Radicalaire (ICR), 27 Bd Jean Moulin, 13385, Marseille, France
| | | | - David Martin
- Univ. Grenoble Alpes, CNRS, DCM, 38000, Grenoble, France
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22
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Harnying W, Sudkaow P, Biswas A, Berkessel A. N-Heterocyclic Carbene/Carboxylic Acid Co-Catalysis Enables Oxidative Esterification of Demanding Aldehydes/Enals, at Low Catalyst Loading. Angew Chem Int Ed Engl 2021; 60:19631-19636. [PMID: 34010504 PMCID: PMC8457137 DOI: 10.1002/anie.202104712] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 05/10/2021] [Indexed: 01/07/2023]
Abstract
We report the discovery that simple carboxylic acids, such as benzoic acid, boost the activity of N-heterocyclic carbene (NHC) catalysts in the oxidative esterification of aldehydes. A simple and efficient protocol for the transformation of a wide range of sterically hindered α- and β-substituted aliphatic aldehydes/enals, catalyzed by a novel and readily accessible N-Mes-/N-2,4,6-trichlorophenyl 1,2,4-triazolium salt, and benzoic acid as co-catalyst, was developed. A whole series of α/β-substituted aliphatic aldehydes/enals hitherto not amenable to NHC-catalyzed esterification could be reacted at typical catalyst loadings of 0.02-1.0 mol %. For benzaldehyde, even 0.005 mol % of NHC catalyst proved sufficient: the lowest value ever achieved in NHC catalysis. Preliminary studies point to carboxylic acid-induced acceleration of acyl transfer from azolium enolate intermediates as the mechanistic basis of the observed effect.
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Affiliation(s)
- Wacharee Harnying
- Department of Chemistry (Organic Chemistry), University of Cologne, Greinstraße 4, 50939, Cologne, Germany
| | - Panyapon Sudkaow
- Department of Chemistry (Organic Chemistry), University of Cologne, Greinstraße 4, 50939, Cologne, Germany
| | - Animesh Biswas
- Department of Chemistry (Organic Chemistry), University of Cologne, Greinstraße 4, 50939, Cologne, Germany
| | - Albrecht Berkessel
- Department of Chemistry (Organic Chemistry), University of Cologne, Greinstraße 4, 50939, Cologne, Germany
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23
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Harnying W, Sudkaow P, Biswas A, Berkessel A. N‐Heterocyclic Carbene/Carboxylic Acid Co‐Catalysis Enables Oxidative Esterification of Demanding Aldehydes/Enals, at Low Catalyst Loading. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202104712] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Wacharee Harnying
- Department of Chemistry (Organic Chemistry) University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Panyapon Sudkaow
- Department of Chemistry (Organic Chemistry) University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Animesh Biswas
- Department of Chemistry (Organic Chemistry) University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Albrecht Berkessel
- Department of Chemistry (Organic Chemistry) University of Cologne Greinstraße 4 50939 Cologne Germany
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24
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Liu MS, Min L, Chen BH, Shu W. Dual Catalysis Relay: Coupling of Aldehydes and Alkenes Enabled by Visible-Light and NHC-Catalyzed Cross-Double C–H Functionalizations. ACS Catal 2021. [DOI: 10.1021/acscatal.1c02890] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Ming-Shang Liu
- Shenzhen Grubbs Institute, Department of Chemistry, and Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen 518055, Guangdong, P.R. China
| | - Lin Min
- Shenzhen Grubbs Institute, Department of Chemistry, and Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen 518055, Guangdong, P.R. China
| | - Bi-Hong Chen
- Shenzhen Grubbs Institute, Department of Chemistry, and Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen 518055, Guangdong, P.R. China
| | - Wei Shu
- Shenzhen Grubbs Institute, Department of Chemistry, and Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen 518055, Guangdong, P.R. China
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Pareek M, Reddi Y, Sunoj RB. Tale of the Breslow intermediate, a central player in N-heterocyclic carbene organocatalysis: then and now. Chem Sci 2021; 12:7973-7992. [PMID: 34194690 PMCID: PMC8208132 DOI: 10.1039/d1sc01910d] [Citation(s) in RCA: 54] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Accepted: 04/28/2021] [Indexed: 12/27/2022] Open
Abstract
N-Heterocyclic carbenes (NHCs) belong to the popular family of organocatalysts used in a wide range of reactions, including that for the synthesis of complex natural products and biologically active compounds. In their organocatalytic manifestation, NHCs are known to impart umpolung reactivity to aldehydes and ketones, which are then exploited in the generation of homoenolate, acyl anion, and enolate equivalents suitable for a plethora of reactions such as annulation, benzoin, Stetter, Claisen rearrangement, cycloaddition, and C-C and C-H bond functionalization reactions and so on. A common thread that runs through these NHC catalyzed reactions is the proposed involvement of an enaminol, also known as the Breslow intermediate, formed by the nucleophilic addition of an NHC to a carbonyl group of a suitable electrophile. In the emerging years of NHC catalysis, enaminol remained elusive and was largely considered a putative intermediate owing to the difficulties encountered in its isolation and characterization. However, in the last decade, synergistic efforts utilizing an array of computational and experimental techniques have helped in gaining important insights into the formation and characterization of Breslow intermediates. Computational studies have suggested that a direct 1,2-proton transfer within the initial zwitterionic intermediate, generated by the action of an NHC on the carbonyl carbon, is energetically prohibitive and hence the participation of other species capable of promoting an assisted proton transfer is more likely. The proton transfer assisted by additives (such as acids, bases, other species, or even a solvent) was found to ease the kinetics of formation of Breslow intermediates. These important details on the formation, in situ detection, isolation, and characterization of the Breslow intermediate are scattered over a series of reports spanning well over a decade, and we intend to consolidate them in this review and provide a critical assessment of these developments. Given the central role of the Breslow intermediate in organocatalytic reactions, this treatise is expected to serve as a valuable source of knowledge on the same.
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Affiliation(s)
- Monika Pareek
- Department of Chemistry, Indian Institute of Technology Bombay Powai Mumbai 400076 India
| | - Yernaidu Reddi
- Department of Chemistry, Indian Institute of Technology Bombay Powai Mumbai 400076 India
| | - Raghavan B Sunoj
- Department of Chemistry, Indian Institute of Technology Bombay Powai Mumbai 400076 India
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Biswas A, Neudörfl JM, Schlörer NE, Berkessel A. Acyl Donor Intermediates in N-Heterocyclic Carbene Catalysis: Acyl Azolium or Azolium Enolate? Angew Chem Int Ed Engl 2021; 60:4507-4511. [PMID: 33140529 PMCID: PMC7986403 DOI: 10.1002/anie.202010348] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 10/20/2020] [Indexed: 11/23/2022]
Abstract
Azolium enolates and acyl azolium cations have been proposed as intermediates in numerous N‐heterocyclic carbene (NHC) catalyzed transformations. Acetyl azolium enolates were generated from the reaction of 2‐propenyl acetate with both saturated (SIPr) and aromatic (IPr) NHCs, isolated, and characterized (NMR, XRD). Protonation with triflic acid gave the corresponding acetyl azolium triflates which were isolated and characterized (NMR, XRD). Acyl azolium cations have been proposed as immediate precursors of the ester product, for example, in the redox esterification of α,β‐enals. Studies with d3‐acetyl azolium triflate suggest that ester formation originates instead from an azolium enolate intermediate. Furthermore, the acetyl azolium enolate selectively reacted with alcohol nucleophiles in the presence of amines. While the acetyl azolium cation did not react with alcohols, an ester‐selective reaction was induced by addition of base, by intermediate formation of the acetyl azolium enolate.
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Affiliation(s)
- Animesh Biswas
- Department of Chemistry (Organic Chemistry), University of Cologne, Greinstraße 4, 50939, Cologne, Germany
| | - Jörg-M Neudörfl
- Department of Chemistry (Organic Chemistry), University of Cologne, Greinstraße 4, 50939, Cologne, Germany
| | - Nils E Schlörer
- Department of Chemistry (Organic Chemistry), University of Cologne, Greinstraße 4, 50939, Cologne, Germany
| | - Albrecht Berkessel
- Department of Chemistry (Organic Chemistry), University of Cologne, Greinstraße 4, 50939, Cologne, Germany
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27
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Biswas A, Neudörfl J, Schlörer NE, Berkessel A. Acyl Donor Intermediates in N‐Heterocyclic Carbene Catalysis: Acyl Azolium or Azolium Enolate? Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202010348] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Animesh Biswas
- Department of Chemistry (Organic Chemistry) University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Jörg‐M. Neudörfl
- Department of Chemistry (Organic Chemistry) University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Nils E. Schlörer
- Department of Chemistry (Organic Chemistry) University of Cologne Greinstraße 4 50939 Cologne Germany
| | - Albrecht Berkessel
- Department of Chemistry (Organic Chemistry) University of Cologne Greinstraße 4 50939 Cologne Germany
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Paul M, Peckelsen K, Thomulka T, Martens J, Berden G, Oomens J, Neudörfl JM, Breugst M, Meijer AJHM, Schäfer M, Berkessel A. Breslow Intermediates (Amino Enols) and Their Keto Tautomers: First Gas-Phase Characterization by IR Ion Spectroscopy. Chemistry 2021; 27:2662-2669. [PMID: 32893891 PMCID: PMC7898712 DOI: 10.1002/chem.202003454] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 09/01/2020] [Indexed: 12/11/2022]
Abstract
Breslow intermediates (BIs) are the crucial nucleophilic amino enol intermediates formed from electrophilic aldehydes in the course of N-heterocyclic carbene (NHC)-catalyzed umpolung reactions. Both in organocatalytic and enzymatic umpolung, the question whether the Breslow intermediate exists as the nucleophilic enol or in the form of its electrophilic keto tautomer is of utmost importance for its reactivity and function. Herein, the preparation of charge-tagged Breslow intermediates/keto tautomers derived from three different types of NHCs (imidazolidin-2-ylidenes, 1,2,4-triazolin-5-ylidenes, thiazolin-2-ylidenes) and aldehydes is reported. An ammonium charge tag is introduced through the aldehyde unit or the NHC. ESI-MS IR ion spectroscopy allowed the unambiguous conclusion that in the gas phase, the imidazolidin-2-ylidene-derived BI indeed exists as a diamino enol, while both 1,2,4-triazolin-5-ylidenes and thiazolin-2-ylidenes give the keto tautomer. This result coincides with the tautomeric states observed for the BIs in solution (NMR) and in the crystalline state (XRD), and is in line with our earlier calculations on the energetics of BI keto-enol equilibria.
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Affiliation(s)
- Mathias Paul
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Katrin Peckelsen
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Thomas Thomulka
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Jonathan Martens
- Institute for Molecules and Materials, FELIX Laboratory, Radboud University, Toernooiveld 7, 6525, ED, Nijmegen, The Netherlands
| | - Giel Berden
- Institute for Molecules and Materials, FELIX Laboratory, Radboud University, Toernooiveld 7, 6525, ED, Nijmegen, The Netherlands
| | - Jos Oomens
- Institute for Molecules and Materials, FELIX Laboratory, Radboud University, Toernooiveld 7, 6525, ED, Nijmegen, The Netherlands.,Van' t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands
| | - Jörg-M Neudörfl
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Martin Breugst
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | | | - Mathias Schäfer
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Albrecht Berkessel
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
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Nakatsuji Y, Kobayashi Y, Masuda S, Takemoto Y. Azolium/Hydroquinone Organo-Radical Co-Catalysis: Aerobic C-C-Bond Cleavage in Ketones. Chemistry 2021; 27:2633-2637. [PMID: 33258523 DOI: 10.1002/chem.202004943] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 11/30/2020] [Indexed: 01/25/2023]
Abstract
Organo-radical catalysts have recently attracted great interest, and the development of this field can be expected to broaden the applications of organocatalysis. Herein, the first example of a radical-generating system is reported that does not require any photoirradiation, radical initiators, or preactivated substrates. The oxidative C-C-bond cleavage of 2-substituted cyclohexanones was achieved using an azolium salt and a hydroquinone as co-catalysts. A catalytic mechanism was proposed based on the results of diffusion-ordered spectroscopy and cyclic voltammetry measurements, as well as computational studies.
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Affiliation(s)
- Yuya Nakatsuji
- Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Shimoadachi-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Yusuke Kobayashi
- Department of Pharmaceutical Chemistry, Kyoto Pharmaceutical University, 1 Misasagishichono-cho, Yamashina-ku, Kyoto, 607-8412, Japan
| | - Sakyo Masuda
- Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Shimoadachi-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Yoshiji Takemoto
- Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Shimoadachi-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
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30
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Liu MS, Shu W. Catalytic, Metal-Free Amide Synthesis from Aldehydes and Imines Enabled by a Dual-Catalyzed Umpolung Strategy under Redox-Neutral Conditions. ACS Catal 2020. [DOI: 10.1021/acscatal.0c04070] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ming-Shang Liu
- Shenzhen Grubbs Institute and Department of Chemistry, Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen 518055, Guangdong, People’s Republic of China
| | - Wei Shu
- Shenzhen Grubbs Institute and Department of Chemistry, Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen 518055, Guangdong, People’s Republic of China
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31
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Zhang Z, Huang S, Huang L, Xu X, Zhao H, Yan X. Synthesis of Mesoionic N-Heterocyclic Olefins and Catalytic Application for Hydroboration Reactions. J Org Chem 2020; 85:12036-12043. [DOI: 10.1021/acs.joc.0c00257] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Zengyu Zhang
- Department of Chemistry, Renmin University of China, Beijing 100872, China
| | - Shiqing Huang
- Department of Chemistry, Renmin University of China, Beijing 100872, China
| | - Linwei Huang
- Department of Chemistry, Renmin University of China, Beijing 100872, China
| | - Xingyu Xu
- Department of Chemistry, Renmin University of China, Beijing 100872, China
| | - Hongyan Zhao
- Department of Chemistry, Renmin University of China, Beijing 100872, China
| | - Xiaoyu Yan
- Department of Chemistry, Renmin University of China, Beijing 100872, China
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32
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Mandal D, Chandra S, Neuman NI, Mahata A, Sarkar A, Kundu A, Anga S, Rawat H, Schulzke C, Mote KR, Sarkar B, Chandrasekhar V, Jana A. Activation of Aromatic C-F Bonds by a N-Heterocyclic Olefin (NHO). Chemistry 2020; 26:5951-5955. [PMID: 32027063 PMCID: PMC7317942 DOI: 10.1002/chem.202000276] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Indexed: 11/09/2022]
Abstract
A N-heterocyclic olefin (NHO), a terminal alkene selectively activates aromatic C-F bonds without the need of any additional catalyst. As a result, a straightforward methodology was developed for the formation of different fluoroaryl-substituted alkenes in which the central carbon-carbon double bond is in a twisted geometry.
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Affiliation(s)
- Debdeep Mandal
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
| | - Shubhadeep Chandra
- Institut für Chemie und BiochemieAnorganische ChemieFreie Universität BerlinFabeckstrasse 34–3614195BerlinGermany
- Institut für Anorganische ChemieLehrstuhl für Anorganische KoordinationschemieUniversität StuttgartPfaffenwaldring 5570569StuttgartGermany
| | - Nicolás I. Neuman
- Institut für Chemie und BiochemieAnorganische ChemieFreie Universität BerlinFabeckstrasse 34–3614195BerlinGermany
- Instituto de Desarrollo Tecnológico para la Industria QuímicaCCT Santa Fe CONICET-UNLColectora Ruta Nacional 168, Km 472, Paraje El Pozo3000Santa FeArgentina
| | - Alok Mahata
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
| | - Arighna Sarkar
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
| | - Abhinanda Kundu
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
| | - Srinivas Anga
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
| | - Hemant Rawat
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
| | - Carola Schulzke
- Institut für BiochemieUniversität GreifswaldFelix-Hausdorff-Strasse 417487GreifswaldGermany
| | - Kaustubh R. Mote
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
| | - Biprajit Sarkar
- Institut für Chemie und BiochemieAnorganische ChemieFreie Universität BerlinFabeckstrasse 34–3614195BerlinGermany
- Institut für Anorganische ChemieLehrstuhl für Anorganische KoordinationschemieUniversität StuttgartPfaffenwaldring 5570569StuttgartGermany
| | - Vadapalli Chandrasekhar
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
- Department of ChemistryIndian Institute of Technology KanpurKanpur208016India
| | - Anukul Jana
- Tata Institute of Fundamental Research HyderabadGopanpally, Hyderabad500107India
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Konstandaras N, Dunn MH, Luis ET, Cole ML, Harper JB. The pK a values of N-aryl imidazolinium salts, their higher homologues, and formamidinium salts in dimethyl sulfoxide. Org Biomol Chem 2020; 18:1910-1917. [PMID: 32095802 DOI: 10.1039/d0ob00036a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A series of imidazolinium salts, their six-, seven- and eight-membered homologues, and the related formamidinium salts were prepared, and their pKa values were determined in DMSO at 25 °C using the bracketing indicator method. The effect of each type of structural variation on the acidity of each salt was considered, particularly noting the importance of ring size and the effect of the steric and electronic nature of the N-aryl substituents. The effect of a cyclic structure was also probed through comparing the cyclic systems with the corresponding formamidinium salts, noting the importance of conformational flexibility in the latter cases. Along with allowing choice of appropriate bases for deprotonation of these species, it is anticipated that the data presented will aid in the understanding of the nucleophilicity, and potentially catalytic efficacy, of the corresponding carbenes.
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Affiliation(s)
- Nicholas Konstandaras
- School of Chemistry, University of New South Wales, UNSW Sydney, NSW 2052, Australia.
| | - Michelle H Dunn
- School of Chemistry, University of New South Wales, UNSW Sydney, NSW 2052, Australia.
| | - Ena T Luis
- School of Chemistry, University of New South Wales, UNSW Sydney, NSW 2052, Australia.
| | - Marcus L Cole
- School of Chemistry, University of New South Wales, UNSW Sydney, NSW 2052, Australia.
| | - Jason B Harper
- School of Chemistry, University of New South Wales, UNSW Sydney, NSW 2052, Australia.
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Abstract
An efficient oxidative NHC-catalyzed one-step transformation of (S)- or (R)-8-oxocitronellal to nepetalactone (NL) in enantio- and diastereomerically pure form has been developed. Several new and "easy to make" N-Mes- or N-Dipp-substituted 1,2,4-triazolium salts carrying nitroaromatic groups on N1 were synthesized and evaluated as precatalysts in combination with base and stoichiometric organic oxidant. Under optimized conditions, NLs are accessible in very good yields and diastereomerically pure under mild conditions. The oxidant used could be recovered and recycled under operationally simple conditions.
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Affiliation(s)
- Wacharee Harnying
- Department of Chemistry (Organic Chemistry) , University of Cologne , Greinstrasse 4 , 50939 Cologne , Germany
| | - Jörg-M Neudörfl
- Department of Chemistry (Organic Chemistry) , University of Cologne , Greinstrasse 4 , 50939 Cologne , Germany
| | - Albrecht Berkessel
- Department of Chemistry (Organic Chemistry) , University of Cologne , Greinstrasse 4 , 50939 Cologne , Germany
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Konstandaras N, Dunn MH, Guerry MS, Barnett CD, Cole ML, Harper JB. The impact of cation structure upon the acidity of triazolium salts in dimethyl sulfoxide. Org Biomol Chem 2019; 18:66-75. [PMID: 31746919 DOI: 10.1039/c9ob02258a] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A series of triazolium salts, selected for their varying electronic and steric properties, were prepared and their pKa values were determined in DMSO at 25 °C using the bracketing indicator method. The effect of each systematic structural variation upon the acidity of the triazolium cation has been considered, in particular examining the effects of systematically altering electronic properties, quantified through the use of Hammett σ parameters. The first pKa value for an azolium salt that generates a mesionic carbene is also reported. These new data allow for the selection of appropriate bases for the deprotonation of such triazolium salts and the potential to correlate the pKa values determined herein with the nucleophilicity of the corresponding carbenes.
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Ghosh A, Barik S, Biju AT. NHC-Catalyzed [3 + 3] Annulation of Thioamides and Modified Enals for the Enantioselective Synthesis of Functionalized Thiazinones. Org Lett 2019; 21:8598-8602. [PMID: 31618035 DOI: 10.1021/acs.orglett.9b03188] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
N-Heterocyclic carbene (NHC)-catalyzed [3 + 3] annulation of thioamides with modified enals allowing the enantioselective synthesis of functionalized 1,3-thiazin-4-ones is reported. The NHC generated from the chiral triazolium salt was optimal and the reaction is initiated by the thia-Michael addition to catalytically generated α,β-unsaturated acylazolium intermediates derived from 2-bromoenals, followed by intramolecular cyclization. This operationally simple procedure offers a straightforward and rapid access to target compounds in moderate to good yields and enantiomeric ratio values.
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Affiliation(s)
- Arghya Ghosh
- Department of Organic Chemistry , Indian Institute of Science , Bangalore - 560012 , India
| | - Soumen Barik
- Department of Organic Chemistry , Indian Institute of Science , Bangalore - 560012 , India
| | - Akkattu T Biju
- Department of Organic Chemistry , Indian Institute of Science , Bangalore - 560012 , India
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