1
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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] [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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2
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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] [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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3
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Fajardo AM, Queyraiux N, Camy A, Vendier L, Grellier M, Del Rosal I, Maron L, Bontemps S. A masked form of an O-borylated Breslow intermediate for the diastereoselective FLP-type activation of aldehydes. Chemistry 2021; 28:e202104122. [PMID: 34964516 DOI: 10.1002/chem.202104122] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Indexed: 11/07/2022]
Abstract
Breslow intermediates are very often elusive species whose application in Frustrated Lewis Pair chemistry is unprecedented. We describe herein the use of a masked form of an O-Borylated Breslow (OBB) intermediate that performs FLP-type activation of the carbonyl function of five different benzaldehyde derivatives with complete diastereoselectivity. The resulting compounds are characterised in solution by NMR spectroscopy (compounds 4 - 8 ) and in solid state by X-Ray diffraction analysis (compounds 4 - 6 ). A combined kinetic and theoretical investigation reveals the associative nature of the rate determining step and suggests that the OBB intermediate part is never released during the whole process.
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Affiliation(s)
| | | | - Aurèle Camy
- Laboratoire de Chimie de Coordination, chemistry, FRANCE
| | - Laure Vendier
- Laboratoire de Chimie de Coordination, chemistry, FRANCE
| | - Mary Grellier
- Laboratoire de Chimie de Coordination, chemistry, FRANCE
| | - Iker Del Rosal
- LPCNO: Laboratoire de physique et chimie des nano-objets, chemistry, FRANCE
| | - Laurent Maron
- LPCNO: Laboratoire de physique et chimie des nano-objets, chemistry, FRANCE
| | - Sébastien Bontemps
- Centre National de la Recherche Scientifique, Laboratoire de Chimie de Coordination, 205 route de Narbonne, 31077 cedex 04, toulouse, FRANCE
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4
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Pearl ES, Fellner DMJ, Söhnel T, Furkert DP, Brimble MA. A Highly Efficient
N
‐Mesityl Thiazolylidene for the Aliphatic Stetter Reaction: Stereoelectronic Quantification for Comparison of N‐Heterocyclic Carbene Organocatalysts. ASIAN J ORG CHEM 2021. [DOI: 10.1002/ajoc.202100445] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Esperanza S. Pearl
- School of Chemical Sciences The University of Auckland 23 Symonds St Auckland 1010 New Zealand
| | - Daniel M. J. Fellner
- School of Chemical Sciences The University of Auckland 23 Symonds St Auckland 1010 New Zealand
| | - Tilo Söhnel
- School of Chemical Sciences The University of Auckland 23 Symonds St Auckland 1010 New Zealand
| | - Daniel P. Furkert
- School of Chemical Sciences The University of Auckland 23 Symonds St Auckland 1010 New Zealand
- Maurice Wilkins Centre for Molecular Biodiscovery 3 Symonds St Auckland 1010 New Zealand
| | - Margaret A. Brimble
- School of Chemical Sciences The University of Auckland 23 Symonds St Auckland 1010 New Zealand
- Maurice Wilkins Centre for Molecular Biodiscovery 3 Symonds St Auckland 1010 New Zealand
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5
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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] [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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7
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Sultane PR, Ahumada G, Janssen‐Müller D, Bielawski CW. Cyclic (Aryl)(Amido)Carbenes: NHCs with Triplet‐like Reactivity. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201910350] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Prakash R. Sultane
- Center for Multidimensional Carbon Materials (CMCM)Institute for Basic Science (IBS) Ulsan 44919 Republic of Korea
| | - Guillermo Ahumada
- Center for Multidimensional Carbon Materials (CMCM)Institute for Basic Science (IBS) Ulsan 44919 Republic of Korea
| | - Daniel Janssen‐Müller
- Organisch-Chemisches InstitutWestfälische Wilhelms-Universität Münster Münster 48149 Germany
| | - Christopher W. Bielawski
- Center for Multidimensional Carbon Materials (CMCM)Institute for Basic Science (IBS) Ulsan 44919 Republic of Korea
- Department Chemistry and Department of Energy EngineeringUlsan National Institute of Science and Technology (UNIST) Ulsan 44919 Republic of Korea
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8
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Sultane PR, Ahumada G, Janssen‐Müller D, Bielawski CW. Cyclic (Aryl)(Amido)Carbenes: NHCs with Triplet‐like Reactivity. Angew Chem Int Ed Engl 2019; 58:16320-16325. [DOI: 10.1002/anie.201910350] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Indexed: 11/05/2022]
Affiliation(s)
- Prakash R. Sultane
- Center for Multidimensional Carbon Materials (CMCM) Institute for Basic Science (IBS) Ulsan 44919 Republic of Korea
| | - Guillermo Ahumada
- Center for Multidimensional Carbon Materials (CMCM) Institute for Basic Science (IBS) Ulsan 44919 Republic of Korea
| | - Daniel Janssen‐Müller
- Organisch-Chemisches Institut Westfälische Wilhelms-Universität Münster Münster 48149 Germany
| | - Christopher W. Bielawski
- Center for Multidimensional Carbon Materials (CMCM) Institute for Basic Science (IBS) Ulsan 44919 Republic of Korea
- Department Chemistry and Department of Energy Engineering Ulsan National Institute of Science and Technology (UNIST) Ulsan 44919 Republic of Korea
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9
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Paul M, Neudörfl JM, Berkessel A. Breslow Intermediates from a Thiazolin-2-ylidene and Fluorinated Aldehydes: XRD and Solution-Phase NMR Spectroscopic Characterization. Angew Chem Int Ed Engl 2019; 58:10596-10600. [PMID: 31131519 DOI: 10.1002/anie.201904308] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Revised: 05/20/2019] [Indexed: 12/20/2022]
Abstract
The first generation and X-ray diffraction (XRD) analysis of a crystalline Breslow intermediate (BI) derived from a thiazolin-2-ylidene, that is, the aromatic heterocycle present in vitamin B1 , is reported. Key to success was the combined use of pentafluorobenzaldehyde and a thiazolin-2-ylidene carrying an enol-stabilizing dispersion energy donor as N-substituent. A so-called primary intermediate (PI) could be isolated in protonated form (pPI) as well and analyzed by XRD. Furthermore, the first stable BI derived from an aromatic thiazolin-2-ylidene and an aliphatic aldehyde (trifluoroacetaldehyde) was prepared and characterized by NMR spectroscopy in solution. When switching to a saturated thiazolidin-2-ylidene, reaction with pentafluorobenzaldehyde afforded a new BI in solution (NMR spectroscopy). Attempts to crystallize the latter BI resulted in the isolation of a novel thiazolidin-2-ylidene dimer that had undergone rearrangement to a hexahydro[1,4]-thiazino[3,2-b]-1,4-thiazine.
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Affiliation(s)
- Mathias Paul
- Cologne University, Department of Chemistry, Greinstrasse 4, 50939, Cologne, Germany
| | - Jörg-M Neudörfl
- Cologne University, Department of Chemistry, Greinstrasse 4, 50939, Cologne, Germany
| | - Albrecht Berkessel
- Cologne University, Department of Chemistry, Greinstrasse 4, 50939, Cologne, Germany
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10
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Paul M, Neudörfl J, Berkessel A. Breslow Intermediates from a Thiazolin‐2‐ylidene and Fluorinated Aldehydes: XRD and Solution‐Phase NMR Spectroscopic Characterization. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201904308] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Mathias Paul
- Cologne UniversityDepartment of Chemistry Greinstrasse 4 50939 Cologne Germany
| | - Jörg‐M. Neudörfl
- Cologne UniversityDepartment of Chemistry Greinstrasse 4 50939 Cologne Germany
| | - Albrecht Berkessel
- Cologne UniversityDepartment of Chemistry Greinstrasse 4 50939 Cologne Germany
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11
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Béthegnies A, Escudié Y, Nuñez‐Dallos N, Vendier L, Hurtado J, del Rosal I, Maron L, Bontemps S. Reductive CO2Homocoupling: Synthesis of a Borylated C3Carbohydrate. ChemCatChem 2018. [DOI: 10.1002/cctc.201801875] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Aurélien Béthegnies
- CNRS, LCC (Laboratoire de Chimie de Coordination) 31077 Toulouse (France) andUniversité de Toulouse UPS, INPT Toulouse 31077 France
| | - Yannick Escudié
- CNRS, LCC (Laboratoire de Chimie de Coordination) 31077 Toulouse (France) andUniversité de Toulouse UPS, INPT Toulouse 31077 France
| | - Nelson Nuñez‐Dallos
- CNRS, LCC (Laboratoire de Chimie de Coordination) 31077 Toulouse (France) andUniversité de Toulouse UPS, INPT Toulouse 31077 France
- Department of ChemistryUniversidad de Los Andes Institution Bogotá 111711 Colombia
| | - Laure Vendier
- CNRS, LCC (Laboratoire de Chimie de Coordination) 31077 Toulouse (France) andUniversité de Toulouse UPS, INPT Toulouse 31077 France
| | - John Hurtado
- Department of ChemistryUniversidad de Los Andes Institution Bogotá 111711 Colombia
| | - Iker del Rosal
- Université de Toulouse and CNRS, INSA, UPS, UMR 5215, LPCNO Toulouse F-31077 France
| | - Laurent Maron
- Université de Toulouse and CNRS, INSA, UPS, UMR 5215, LPCNO Toulouse F-31077 France
| | - Sébastien Bontemps
- CNRS, LCC (Laboratoire de Chimie de Coordination) 31077 Toulouse (France) andUniversité de Toulouse UPS, INPT Toulouse 31077 France
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12
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Hsu N, Wang Y, Lin K, Chang C, Ke S, Lyu S, Hsu L, Li Y, Chen S, Wang K, Li T. Evidence of Diradicals Involved in the Yeast Transketolase Catalyzed Keto-Transferring Reactions. Chembiochem 2018; 19:2395-2402. [PMID: 30155962 PMCID: PMC6282555 DOI: 10.1002/cbic.201800378] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2018] [Indexed: 11/12/2022]
Abstract
Transketolase (TK) catalyzes a reversible transfer of a two-carbon (C2 ) unit between phosphoketose donors and phosphoaldose acceptors, for which the group-transfer reaction that follows a one- or two-electron mechanism and the force that breaks the C2"-C3" bond of the ketose donors remain unresolved. Herein, we report ultrahigh-resolution crystal structures of a TK (TKps) from Pichia stipitis in previously undiscovered intermediate states and support a diradical mechanism for a reversible group-transfer reaction. In conjunction with MS, NMR spectroscopy, EPR and computational analyses, it is concluded that the enzyme-catalyzed non-Kekulé diradical cofactor brings about the C2"-C3" bond cleavage/formation for the C2 -unit transfer reaction, for which suppression of activation energy and activation and destabilization of enzymatic intermediates are facilitated.
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Affiliation(s)
- Ning‐Shian Hsu
- Genomics Research CenterAcademia SinicaTaipei115Taiwan
- Institute of Biochemistry and Molecular BiologyNational Yang-Ming UniversityTaipei112Taiwan
| | - Yung‐Lin Wang
- Genomics Research CenterAcademia SinicaTaipei115Taiwan
| | - Kuan‐Hung Lin
- Genomics Research CenterAcademia SinicaTaipei115Taiwan
- Institute of Biochemistry and Molecular BiologyNational Yang-Ming UniversityTaipei112Taiwan
| | - Chi‐Fon Chang
- Genomics Research CenterAcademia SinicaTaipei115Taiwan
| | - Shyue‐Chu Ke
- Department of PhysicsNational Dong Hwa UniversityHualien974Taiwan
| | - Syue‐Yi Lyu
- Genomics Research CenterAcademia SinicaTaipei115Taiwan
| | - Li‐Jen Hsu
- Genomics Research CenterAcademia SinicaTaipei115Taiwan
| | - Yi‐Shan Li
- Genomics Research CenterAcademia SinicaTaipei115Taiwan
| | | | | | - Tsung‐Lin Li
- Genomics Research CenterAcademia SinicaTaipei115Taiwan
- Biotechnology CenterNational Chung Hsing UniversityTaichung City402Taiwan
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13
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Phan J, Ruser SM, Zeitler K, Rehbein J. NHC-Stabilized Radicals in the Formal Hydroacylation Reaction of Alkynes. European J Org Chem 2018. [DOI: 10.1002/ejoc.201801185] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Jenny Phan
- Fakultät für Chemie und Pharmazie; Universität Regensburg; Institut für Organische Chemie; Universitätsstrasse 1 93053 Regensburg Germany
| | - Stephanie-M. Ruser
- Fachbereich Chemie; Universität Hamburg; Institut für Organische Chemie; Martin-Luther-King-Platz 6 20146 Hamburg Germany
| | - Kirsten Zeitler
- Institut für Organische Chemie; Universität Leipzig; Johannis-Allee 29 04103 Leipzig Germany
| | - Julia Rehbein
- Fakultät für Chemie und Pharmazie; Universität Regensburg; Institut für Organische Chemie; Universitätsstrasse 1 93053 Regensburg Germany
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14
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Paul M, Sudkaow P, Wessels A, Schlörer NE, Neudörfl J, Berkessel A. Breslow Intermediates from Aromatic N‐Heterocyclic Carbenes (Benzimidazolin‐2‐ylidenes, Thiazolin‐2‐ylidenes). Angew Chem Int Ed Engl 2018; 57:8310-8315. [PMID: 29645334 DOI: 10.1002/anie.201801676] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Indexed: 12/29/2022]
Affiliation(s)
- Mathias Paul
- Cologne UniversityDepartment of Chemistry, Organic Chemistry Greinstrasse 4 50939 Cologne Germany
| | - Panyapon Sudkaow
- Cologne UniversityDepartment of Chemistry, Organic Chemistry Greinstrasse 4 50939 Cologne Germany
| | - Alina Wessels
- Cologne UniversityDepartment of Chemistry, Organic Chemistry Greinstrasse 4 50939 Cologne Germany
| | - Nils E. Schlörer
- Cologne UniversityDepartment of Chemistry, Organic Chemistry Greinstrasse 4 50939 Cologne Germany
| | - Jörg‐M. Neudörfl
- Cologne UniversityDepartment of Chemistry, Organic Chemistry Greinstrasse 4 50939 Cologne Germany
| | - Albrecht Berkessel
- Cologne UniversityDepartment of Chemistry, Organic Chemistry Greinstrasse 4 50939 Cologne Germany
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15
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Paul M, Sudkaow P, Wessels A, Schlörer NE, Neudörfl J, Berkessel A. Breslow‐Intermediate aromatischer N‐heterocyclischer Carbene (Benzimidazolin‐2‐ylidene, Thiazolin‐2‐ylidene). Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201801676] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Mathias Paul
- Universität zu KölnDepartment für ChemieOrganische Chemie Greinstraße 4 50939 Köln Deutschland
| | - Panyapon Sudkaow
- Universität zu KölnDepartment für ChemieOrganische Chemie Greinstraße 4 50939 Köln Deutschland
| | - Alina Wessels
- Universität zu KölnDepartment für ChemieOrganische Chemie Greinstraße 4 50939 Köln Deutschland
| | - Nils E. Schlörer
- Universität zu KölnDepartment für ChemieOrganische Chemie Greinstraße 4 50939 Köln Deutschland
| | - Jörg‐M. Neudörfl
- Universität zu KölnDepartment für ChemieOrganische Chemie Greinstraße 4 50939 Köln Deutschland
| | - Albrecht Berkessel
- Universität zu KölnDepartment für ChemieOrganische Chemie Greinstraße 4 50939 Köln Deutschland
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16
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Nair V, Menon RS. Nucleophile‐Initiated Catalytic and Multicomponent Reactions. CHEM REC 2018; 19:347-361. [DOI: 10.1002/tcr.201800027] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 06/08/2018] [Indexed: 11/11/2022]
Affiliation(s)
- Vijay Nair
- Organic Chemistry SectionCSIR-National Institute for Interdisciplinary Science and Technology Trivandrum 695 019 India
| | - Rajeev S. Menon
- Department of ChemistryCentral University of Haryana Mahendergarh 123 031, Haryana India
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17
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Singh A, Kumar A. Benzoin Condensation: A Kinetic Monitoring at the Oil-Water Interface. ChemistrySelect 2018. [DOI: 10.1002/slct.201703107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Anshu Singh
- Department of Chemistry; Banaras Hindu University; 221005 India
| | - Anil Kumar
- Physical and Materials Chemistry Division; CSIR-National Chemical Laboratory; Homi Bhabha Road Pune-411 008 India
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18
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Hsu NS, Wang YL, Lin KH, Chang CF, Lyu SY, Hsu LJ, Liu YC, Chang CY, Wu CJ, Li TL. The Mesomeric Effect of Thiazolium on non-Kekulé Diradicals in Pichia stipitis
Transketolase. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201709799] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Ning-Shian Hsu
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
- Institute of Biochemistry and Molecular Biology; National Yang-Ming University; Taipei 112 Taiwan
| | - Yung-Lin Wang
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Kuan-Hung Lin
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
- Institute of Biochemistry and Molecular Biology; National Yang-Ming University; Taipei 112 Taiwan
| | - Chi-Fon Chang
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Syue-Yi Lyu
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Li-Jen Hsu
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Yu-Chen Liu
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Chin-Yuan Chang
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Chang-Jer Wu
- Department of Food Science; National (Taiwan) Ocean University; Keelung 202 Taiwan
| | - Tsung-Lin Li
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
- Biotechnology Center; National Chung Hsing University; Taichung City 402 Taiwan
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19
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Hsu NS, Wang YL, Lin KH, Chang CF, Lyu SY, Hsu LJ, Liu YC, Chang CY, Wu CJ, Li TL. The Mesomeric Effect of Thiazolium on non-Kekulé Diradicals in Pichia stipitis
Transketolase. Angew Chem Int Ed Engl 2018; 57:1802-1807. [DOI: 10.1002/anie.201709799] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Revised: 11/23/2017] [Indexed: 11/07/2022]
Affiliation(s)
- Ning-Shian Hsu
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
- Institute of Biochemistry and Molecular Biology; National Yang-Ming University; Taipei 112 Taiwan
| | - Yung-Lin Wang
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Kuan-Hung Lin
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
- Institute of Biochemistry and Molecular Biology; National Yang-Ming University; Taipei 112 Taiwan
| | - Chi-Fon Chang
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Syue-Yi Lyu
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Li-Jen Hsu
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Yu-Chen Liu
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Chin-Yuan Chang
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
| | - Chang-Jer Wu
- Department of Food Science; National (Taiwan) Ocean University; Keelung 202 Taiwan
| | - Tsung-Lin Li
- Genomics Research Center; Academia Sinica; Taipei 115 Taiwan
- Biotechnology Center; National Chung Hsing University; Taichung City 402 Taiwan
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20
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Gehrke S, Hollóczki O. Treten in der N-heterozyklischen Carben-Organokatalyse wirklich Carbene auf? Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201708305] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Sascha Gehrke
- Mulliken Center für Theoretische Chemie; Rheinische Friedrich-Wilhelms-Universität Bonn; Beringstraße 4+6 53115 Bonn Deutschland
- Max-Planck-Institut für Chemische Energiekonversion; Stiftstraße 34-36 45470 Mülheim an der Ruhr Deutschland
| | - Oldamur Hollóczki
- Mulliken Center für Theoretische Chemie; Rheinische Friedrich-Wilhelms-Universität Bonn; Beringstraße 4+6 53115 Bonn Deutschland
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21
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Gehrke S, Hollóczki O. Are There Carbenes in N-Heterocyclic Carbene Organocatalysis? Angew Chem Int Ed Engl 2017; 56:16395-16398. [PMID: 29072807 DOI: 10.1002/anie.201708305] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2017] [Revised: 10/23/2017] [Indexed: 11/08/2022]
Abstract
Azolium cations are widely employed in organocatalysis to catalyse highly valuable synthetic processes in the presence of a base. These reactions are called "N-heterocyclic carbene catalysis", based on the assumption that they are initiated by the formation of a free carbene through deprotonation, which can then react with the substrates and thereby affect their reactivity to obtain the desired products. However, we herein provide evidence that an electrophilic aromatic substitution mechanism is energetically more favourable, in which the azolium cation reacts directly with the substrate, avoiding the formation of the free carbene in solution.
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Affiliation(s)
- Sascha Gehrke
- Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstrasse 4+6, 53115, Bonn, Germany.,Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470, Muelheim an der Ruhr, Germany
| | - Oldamur Hollóczki
- Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstrasse 4+6, 53115, Bonn, Germany
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22
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Yatham VR, Harnying W, Kootz D, Neudörfl JM, Schlörer NE, Berkessel A. 1,4-Bis-Dipp/Mes-1,2,4-Triazolylidenes: Carbene Catalysts That Efficiently Overcome Steric Hindrance in the Redox Esterification of α- and β-Substituted α,β-Enals. J Am Chem Soc 2016; 138:2670-7. [PMID: 26797403 DOI: 10.1021/jacs.5b11796] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
As reported by Scheidt and Bode in 2005, sterically nonencumbered α,β-enals are readily converted to saturated esters in the presence of alcohols and N-heterocyclic carbene catalysts, e.g., benzimidazolylidenes or triazolylidenes. However, substituents at the α- or β-position of the α,β-enal substrate are typically not tolerated, thus severely limiting the substrate spectrum. On the basis of our earlier mechanistic studies, a set of N-Mes- or N-Dipp-substituted 1,2,4-triazolium salts were synthesized and evaluated as (pre)catalysts in the redox esterification of various α- or β-substituted enals. In particular the 1,4-bis-Mes/Dipp-1,2,4-triazolylidenes overcome the above limitations and efficiently catalyze the redox esterification of a whole series of α/β-substituted enals hitherto not amenable to NHC-catalyzed transformations. The synthetic value of 1,4-bis-Mes/Dipp-1,2,4-triazolylidenes is further demonstrated by the one-step bicyclization of 10-oxocitral to (racemic) nepetalactone in diastereomerically pure form.
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Affiliation(s)
- Veera Reddy Yatham
- Department of Chemistry (Organic Chemistry), University of Cologne , Greinstrasse 4, 50939 Cologne, Germany
| | - Wacharee Harnying
- Department of Chemistry (Organic Chemistry), University of Cologne , Greinstrasse 4, 50939 Cologne, Germany
| | - Darius Kootz
- 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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23
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Collett CJ, Massey RS, Taylor JE, Maguire OR, O'Donoghue AC, Smith AD. Rate and equilibrium constants for the addition of N-heterocyclic carbenes into benzaldehydes: a remarkable 2-substituent effect. Angew Chem Int Ed Engl 2015; 54:6887-92. [PMID: 25908493 PMCID: PMC4510784 DOI: 10.1002/anie.201501840] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Indexed: 11/23/2022]
Abstract
Rate and equilibrium constants for the reaction between N-aryl triazolium N-heterocyclic carbene (NHC) precatalysts and substituted benzaldehyde derivatives to form 3-(hydroxybenzyl)azolium adducts under both catalytic and stoichiometric conditions have been measured. Kinetic analysis and reaction profile fitting of both the forward and reverse reactions, plus onwards reaction to the Breslow intermediate, demonstrate the remarkable effect of the benzaldehyde 2-substituent in these reactions and provide insight into the chemoselectivity of cross-benzoin reactions.
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Affiliation(s)
- Christopher J Collett
- EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST (UK) http://ch-www.st-andrews.ac.uk/staff/ads/group/
| | - Richard S Massey
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE (UK)
| | - James E Taylor
- EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST (UK) http://ch-www.st-andrews.ac.uk/staff/ads/group/
| | - Oliver R Maguire
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE (UK)
| | | | - Andrew D Smith
- EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST (UK) http://ch-www.st-andrews.ac.uk/staff/ads/group/.
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24
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Collett CJ, Massey RS, Taylor JE, Maguire OR, O'Donoghue AC, Smith AD. Rate and Equilibrium Constants for the Addition of N-Heterocyclic Carbenes into Benzaldehydes: A Remarkable 2-Substituent Effect. ACTA ACUST UNITED AC 2015; 127:6991-6996. [PMID: 27478264 PMCID: PMC4955233 DOI: 10.1002/ange.201501840] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Indexed: 12/01/2022]
Abstract
Rate and equilibrium constants for the reaction between N‐aryl triazolium N‐heterocyclic carbene (NHC) precatalysts and substituted benzaldehyde derivatives to form 3‐(hydroxybenzyl)azolium adducts under both catalytic and stoichiometric conditions have been measured. Kinetic analysis and reaction profile fitting of both the forward and reverse reactions, plus onwards reaction to the Breslow intermediate, demonstrate the remarkable effect of the benzaldehyde 2‐substituent in these reactions and provide insight into the chemoselectivity of cross‐benzoin reactions.
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Affiliation(s)
- Christopher J. Collett
- EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST (UK) http://ch‐www.st‐andrews.ac.uk/staff/ads/group/
| | - Richard S. Massey
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE (UK)
| | - James E. Taylor
- EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST (UK) http://ch‐www.st‐andrews.ac.uk/staff/ads/group/
| | - Oliver R. Maguire
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE (UK)
| | | | - Andrew D. Smith
- EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST (UK) http://ch‐www.st‐andrews.ac.uk/staff/ads/group/
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25
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Holland MC, Gilmour R. Deconstructing Covalent Organocatalysis. Angew Chem Int Ed Engl 2015; 54:3862-71. [DOI: 10.1002/anie.201409004] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Indexed: 01/15/2023]
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26
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27
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Hong M, Chen EYX. Proton-Transfer Polymerization (HTP): Converting Methacrylates to Polyesters by an N-Heterocyclic Carbene. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201406630] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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28
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Hong M, Chen EYX. Proton-Transfer Polymerization (HTP): Converting Methacrylates to Polyesters by an N-Heterocyclic Carbene. Angew Chem Int Ed Engl 2014; 53:11900-6. [DOI: 10.1002/anie.201406630] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 08/13/2014] [Indexed: 01/21/2023]
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29
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Nzahou Ottou W, Bourichon D, Vignolle J, Wirotius AL, Robert F, Landais Y, Sotiropoulos JM, Miqueu K, Taton D. Cyclodimerization versus Polymerization of Methyl Methacrylate Induced byN-Heterocyclic Carbenes: A Combined Experimental and Theoretical Study. Chemistry 2014; 20:3989-97. [DOI: 10.1002/chem.201304492] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2013] [Indexed: 11/09/2022]
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30
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Berkessel A, Elfert S. On the Involvement of a Spiroepoxide Intermediate in N-Heterocyclic Carbene (NHC)-Catalyzed Benzoin Condensations - An Approach by Oxygenation of Deoxy-Breslow Intermediates. Adv Synth Catal 2014. [DOI: 10.1002/adsc.201300801] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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31
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César V, Labat S, Miqueu K, Sotiropoulos JM, Brousses R, Lugan N, Lavigne G. The ambivalent chemistry of a free anionic N-heterocyclic carbene decorated with a malonate backbone: the plus of a negative charge. Chemistry 2013; 19:17113-24. [PMID: 24307368 DOI: 10.1002/chem.201303184] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Indexed: 11/08/2022]
Abstract
The anionic heterocycle "[maloNHC](-)", ([1](-)), is the archetype of a growing family of N-heterocyclic carbenes incorporating an anionic backbone; here, a malonate group. A comprehensive experimental exploration of its chemistry as a free entity (in the form of its lithium salt [1]·Li) is presented, and rationalized using DFT calculations at the B3LYP/6-31+G** level of theory. For the sake of comparison, similar computations were performed on other representative carbene types. Reactions of [1]·Li with a broad series of electrophilic reagents were used to ascertain its intrinsic nature as a nucleophilic carbene. Unexpectedly, [1]·Li was also seen to react with the nucleophilic tert-butylisocyanide, to give an anionic ketenimine, which could be subsequently derivatized, either into an imine by protonation of the ketenimine moiety, or into a neutral ketenimine by alkylation of the intracyclic malonate moiety. Further experiments on the electrophilic behavior of [1]·Li revealed its unexpected reactivity toward p-chlorobenzaldehyde, resulting in a formal C-H activation and the first structurally characterized keto-tautomer of the Breslow intermediate. Finally, [1]·Li remarkably activates polar E-H bonds, including N-H bonds from ammonia and amines, Si-H bonds, and B-H bonds. Importantly, DFT calculations indicate the importance of counterion effects. In particular, the key to the observed reactivity appears to be a modulation of energy levels associated with a dynamic variability of the Li-O distance between the remote malonate group and the counterion.
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Affiliation(s)
- Vincent César
- CNRS, LCC (laboratoire de chimie de coordination), 205 route de Narbonne, BP44099, 31077 Toulouse Cedex 4 (France); Université de Toulouse, UPS, INPT, 31077 Toulouse (France).
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32
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Berkessel A, Yatham VR, Elfert S, Neudörfl JM. Charakterisierung der Schlüsselintermediate von carbenkatalysierten Umpolungen durch Kristallstrukturanalyse/NMR-Spektroskopie: Breslow-Intermediate, Homoenolate und Azoliumenolate. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201303107] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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33
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Berkessel A, Yatham VR, Elfert S, Neudörfl JM. Characterization of the Key Intermediates of Carbene-Catalyzed Umpolung by NMR Spectroscopy and X-Ray Diffraction: Breslow Intermediates, Homoenolates, and Azolium Enolates. Angew Chem Int Ed Engl 2013; 52:11158-62. [DOI: 10.1002/anie.201303107] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2013] [Indexed: 12/24/2022]
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34
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35
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Diederich F. 125 Years of Chemistry in the Mirror of “Angewandte”. Angew Chem Int Ed Engl 2013; 52:2714-42. [DOI: 10.1002/anie.201300056] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2013] [Indexed: 01/09/2023]
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36
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Schedler M, Wang DS, Glorius F. NHC-Catalyzed Hydroacylation of Styrenes. Angew Chem Int Ed Engl 2013; 52:2585-9. [DOI: 10.1002/anie.201209291] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2012] [Indexed: 11/07/2022]
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37
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38
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Berkessel A, Elfert S, Yatham VR, Neudörfl JM, Schlörer NE, Teles JH. Umpolung by N-Heterocyclic Carbenes: Generation and Reactivity of the Elusive 2,2-Diamino Enols (Breslow Intermediates). Angew Chem Int Ed Engl 2012; 51:12370-4. [DOI: 10.1002/anie.201205878] [Citation(s) in RCA: 155] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Revised: 08/31/2012] [Indexed: 01/27/2023]
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39
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Berkessel A, Elfert S, Yatham VR, Neudörfl JM, Schlörer NE, Teles JH. Umpolung mit N-heterocyclischen Carbenen: Generierung und Reaktivität von Breslow-Intermediaten (2,2-Diaminoenole). Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201205878] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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40
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Müller T, Badu-Tawiah A, Cooks RG. Accelerated CarbonCarbon Bond-Forming Reactions in Preparative Electrospray. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201206632] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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41
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Müller T, Badu-Tawiah A, Cooks RG. Accelerated carbon-carbon bond-forming reactions in preparative electrospray. Angew Chem Int Ed Engl 2012; 51:11832-5. [PMID: 23042619 DOI: 10.1002/anie.201206632] [Citation(s) in RCA: 152] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Revised: 09/17/2012] [Indexed: 11/07/2022]
Affiliation(s)
- Thomas Müller
- Institute of Organic Chemistry, University of Innsbruck, 6020 Innsbruck, Austria.
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42
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Maji B, Mayr H. Structures and Reactivities of O-Methylated Breslow Intermediates. Angew Chem Int Ed Engl 2012; 51:10408-12. [DOI: 10.1002/anie.201204524] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Indexed: 11/12/2022]
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43
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Maji B, Horn M, Mayr H. Nucleophilic Reactivities of Deoxy Breslow Intermediates: How Does Aromaticity Affect the Catalytic Activities of N-Heterocyclic Carbenes? Angew Chem Int Ed Engl 2012; 51:6231-5. [DOI: 10.1002/anie.201202327] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Indexed: 11/05/2022]
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45
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Maji B, Horn M, Mayr H. Nucleophile Reaktivitäten von Desoxy-Breslow-Intermediaten: Wie beeinflusst Aromatizität die katalytische Aktivität N-heterocyclischer Carbene? Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201202327] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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46
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Hans M, Wouters J, Demonceau A, Delaude L. Synthesis and Organocatalytic Applications of Imidazol(in)ium-2-thiocarboxylates. European J Org Chem 2011. [DOI: 10.1002/ejoc.201101286] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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47
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Maji B, Breugst M, Mayr H. N-Heterocyclic Carbenes: Organocatalysts with Moderate Nucleophilicity but Extraordinarily High Lewis Basicity. Angew Chem Int Ed Engl 2011; 50:6915-9. [DOI: 10.1002/anie.201102435] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Indexed: 11/07/2022]
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48
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Maji B, Breugst M, Mayr H. N-Heterocyclische Carbene: Organokatalysatoren mit mäßiger Nucleophilie, aber außerordentlich hoher Lewis-Basizität. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201102435] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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49
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De Sarkar S, Studer A. NHC-Catalyzed Michael Addition to α,β-Unsaturated Aldehydes by Redox Activation. Angew Chem Int Ed Engl 2010; 49:9266-9. [DOI: 10.1002/anie.201004593] [Citation(s) in RCA: 301] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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50
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De Sarkar S, Studer A. NHC-katalysierte Michael-Additionen an α,β-ungesättigte Aldehyde unter Redoxaktivierung. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201004593] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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