51
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Hong M, Tang X, Falivene L, Caporaso L, Cavallo L, Chen EYX. Proton-Transfer Polymerization by N-Heterocyclic Carbenes: Monomer and Catalyst Scopes and Mechanism for Converting Dimethacrylates into Unsaturated Polyesters. J Am Chem Soc 2016; 138:2021-35. [PMID: 26779897 DOI: 10.1021/jacs.5b13019] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
This contribution presents a full account of experimental and theoretical/computational investigations into the N-heterocyclic carbene (NHC)-catalyzed proton-transfer polymerization (HTP) that converts common dimethacrylates (DMAs) containing no protic groups into unsaturated polyesters. This new HTP proceeds through the step-growth propagation cycles via enamine intermediates, consisting of the proposed conjugate addition-proton transfer-NHC release fundamental steps. This study examines the monomer and catalyst scopes as well as the fundamental steps involved in the overall HTP mechanism. DMAs having six different types of linkages connecting the two methacrylates have been polymerized into the corresponding unsaturated polyesters. The most intriguing unsaturated polyester of the series is that based on the biomass-derived furfuryl dimethacrylate, which showed a unique self-curing ability. Four MeO- and Cl-substituted TPT (1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene) derivatives as methanol insertion products, (Rx)TPT(MeO/H) (R = MeO, Cl; x = 2, 3), and two free carbenes (catalysts), (OMe2)TPT and (OMe3)TPT, have been synthesized, while (OMe2)TPT(MeO/H) and (OMe2)TPT have also been structurally characterized. The structure/reactivity relationship study revealed that (OMe2)TPT, being both a strong nucleophile and a good leaving group, exhibits the highest HTP activity and also produced the polyester with the highest Mn, while the Cl-substituted TPT derivatives are least active and efficient. Computational studies have provided mechanistic insights into the tail-to-tail dimerization coupling step as a suitable model for the propagation cycle of the HTP. The extensive energy profile was mapped out, and the experimentally observed unicity of the TPT-based catalysts was satisfactorily explained with the thermodynamic formation of key spirocyclic species.
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Affiliation(s)
- Miao Hong
- Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523-1872, United States
| | - Xiaoyan Tang
- Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523-1872, United States
| | - Laura Falivene
- King Abdullah University of Science and Technology (KAUST), Physical Sciences and Engineering Division, Kaust Catalysis Center, Thuwal 23955-6900, Saudi Arabia.,Dipartimento di Chimica e Biologia, Università di Salerno , Via Papa Paolo Giovanni II, I-84084, Fisciano, Italy
| | - Lucia Caporaso
- Dipartimento di Chimica e Biologia, Università di Salerno , Via Papa Paolo Giovanni II, I-84084, Fisciano, Italy
| | - Luigi Cavallo
- King Abdullah University of Science and Technology (KAUST), Physical Sciences and Engineering Division, Kaust Catalysis Center, Thuwal 23955-6900, Saudi Arabia.,Dipartimento di Chimica e Biologia, Università di Salerno , Via Papa Paolo Giovanni II, I-84084, Fisciano, Italy
| | - Eugene Y-X Chen
- Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523-1872, United States
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52
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N -Heterocyclic carbene catalyzed tail-to-tail oligomerization of N , N -dimethylacrylamide (DMAA) and the search for the Stetter reaction of DMAA with benzaldehyde. Tetrahedron Lett 2015. [DOI: 10.1016/j.tetlet.2015.09.104] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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53
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Rehbein J, Ruser SM, Phan J. NHC-catalysed benzoin condensation - is it all down to the Breslow intermediate? Chem Sci 2015; 6:6013-6018. [PMID: 29449915 PMCID: PMC5669215 DOI: 10.1039/c5sc02186c] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 07/20/2015] [Indexed: 11/21/2022] Open
Abstract
The Breslow catalytic cycle describing the benzoin condensation promoted by N-heterocyclic carbenes (NHC) as proposed in the late 1950s has since then been tried by generations of physical organic chemists. Emphasis has been laid on proofing the existence of an enaminol like structure (Breslow intermediate) that explains the observed umpolung of an otherwise electrophilic aldehyde. The present study is not focusing on spectroscopic elucidation of a thiazolydene based Breslow intermediate but rather tries to clarify if this key-intermediate is indeed directly linked with the product side of the overall reaction. The here presented EPR-spectroscopic and computational data provide a fundamentally different view on how the benzoin condensation may proceed: a radical pair could be identified as a second key-intermediate that is derived from the Breslow-intermediate via an SET process. These results highlight the close relationship to the Cannizarro reaction and oxidative transformations of aldehydes under NHC catalysis.
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Affiliation(s)
- Julia Rehbein
- Organische Chemie , Universität Hamburg , Martin-Luther-King-Platz 6 , Germany .
| | - Stephanie-M Ruser
- Organische Chemie , Universität Hamburg , Martin-Luther-King-Platz 6 , Germany .
| | - Jenny Phan
- Organische Chemie , Universität Hamburg , Martin-Luther-King-Platz 6 , Germany .
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54
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Tian Y, Lee JK. Gas Phase Studies of N-Heterocyclic Carbene-Catalyzed Condensation Reactions. J Org Chem 2015; 80:6831-8. [PMID: 26066314 DOI: 10.1021/acs.joc.5b01069] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
N-Heterocyclic carbenes (NHCs) catalyze Umpolung condensation reactions of carbonyl compounds, including the Stetter reaction. These types of reactions have not heretofore been examined in the gas phase. Herein, we explore the feasibility of examining these reactions in the absence of solvent. A charge-tagged thiazolylidene catalyst is used to track the reactions by mass spectrometry. We find that the first Umpolung step, the addition of the NHC catalyst to a carbonyl compound to form the "Breslow intermediate", does not readily proceed in the gas phase, contrary to the case in solution. The use of acylsilanes in place of the carbonyl compounds appears to solve this issue, presumably because of a favorable Brook rearrangement. The second addition reaction, with enones, does not occur under our gas phase conditions. These reactions do occur in solution; the differential reactivity between the condensed and gas phases is discussed, and calculations are used to aid in the interpretation of the results.
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Affiliation(s)
- Yuan Tian
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, United States
| | - Jeehiun K Lee
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, United States
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55
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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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56
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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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57
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Langdon SM, Legault CY, Gravel M. Origin of Chemoselectivity in N-Heterocyclic Carbene Catalyzed Cross-Benzoin Reactions: DFT and Experimental Insights. J Org Chem 2015; 80:3597-610. [DOI: 10.1021/acs.joc.5b00301] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Steven M. Langdon
- Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada
| | - Claude Y. Legault
- Département de Chimie, Université de Sherbrooke, 2500 Boulevard Université, Sherbrooke, Quebec J1K 2R1, Canada
| | - Michel Gravel
- Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada
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58
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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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59
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60
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Neumann P, Tittmann K. Marvels of enzyme catalysis at true atomic resolution: distortions, bond elongations, hidden flips, protonation states and atom identities. Curr Opin Struct Biol 2014; 29:122-33. [PMID: 25460275 DOI: 10.1016/j.sbi.2014.11.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 10/31/2014] [Accepted: 11/03/2014] [Indexed: 10/24/2022]
Abstract
Although general principles of enzyme catalysis are fairly well understood nowadays, many important details of how exactly the substrate is bound and processed in an enzyme remain often invisible and as such elusive. In fortunate cases, structural analysis of enzymes can be accomplished at true atomic resolution thus making possible to shed light on otherwise concealed fine-structural traits of bound substrates, intermediates, cofactors and protein groups. We highlight recent structural studies of enzymes using ultrahigh-resolution X-ray protein crystallography showcasing its enormous potential as a tool in the elucidation of enzymatic mechanisms and in unveiling fundamental principles of enzyme catalysis. We discuss the observation of seemingly hyper-reactive, physically distorted cofactors and intermediates with elongated scissile substrate bonds, the detection of 'hidden' conformational and chemical equilibria and the analysis of protonation states with surprising findings. In delicate cases, atomic resolution is required to unambiguously disclose the identity of atoms as demonstrated for the metal cluster in nitrogenase. In addition to the pivotal structural findings and the implications for our understanding of enzyme catalysis, we further provide a practical framework for resolution enhancement through optimized data acquisition and processing.
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Affiliation(s)
- Piotr Neumann
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Justus-von-Liebig-Weg 11, Georg-August-Universität Göttingen, Göttingen D-37077, Germany.
| | - Kai Tittmann
- Abteilung Molekulare Enzymologie, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Justus-von-Liebig-Weg 11, Georg-August-Universität Göttingen, Göttingen D-37077, Germany.
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61
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Tittmann K. Sweet siblings with different faces: the mechanisms of FBP and F6P aldolase, transaldolase, transketolase and phosphoketolase revisited in light of recent structural data. Bioorg Chem 2014; 57:263-280. [PMID: 25267444 DOI: 10.1016/j.bioorg.2014.09.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Revised: 08/25/2014] [Accepted: 09/01/2014] [Indexed: 10/24/2022]
Abstract
Nature has evolved different strategies for the reversible cleavage of ketose phosphosugars as essential metabolic reactions in all domains of life. Prominent examples are the Schiff-base forming class I FBP and F6P aldolase as well as transaldolase, which all exploit an active center lysine to reversibly cleave the C3-C4 bond of fructose-1,6-bisphosphate or fructose-6-phosphate to give two 3-carbon products (aldolase), or to shuttle 3-carbon units between various phosphosugars (transaldolase). In contrast, transketolase and phosphoketolase make use of the bioorganic cofactor thiamin diphosphate to cleave the preceding C2-C3 bond of ketose phosphates. While transketolase catalyzes the reversible transfer of 2-carbon ketol fragments in a reaction analogous to that of transaldolase, phosphoketolase forms acetyl phosphate as final product in a reaction that comprises ketol cleavage, dehydration and phosphorolysis. In this review, common and divergent catalytic principles of these enzymes will be discussed, mostly, but not exclusively, on the basis of crystallographic snapshots of catalysis. These studies in combination with mutagenesis and kinetic analysis not only delineated the stereochemical course of substrate binding and processing, but also identified key catalytic players acting at the various stages of the reaction. The structural basis for the different chemical fates and lifetimes of the central enamine intermediates in all five enzymes will be particularly discussed, in addition to the mechanisms of substrate cleavage, dehydration and ring-opening reactions of cyclic substrates. The observation of covalent enzymatic intermediates in hyperreactive conformations such as Schiff-bases with twisted double-bond linkages in transaldolase and physically distorted substrate-thiamin conjugates with elongated substrate bonds to be cleaved in transketolase, which probably epitomize a canonical feature of enzyme catalysis, will be also highlighted.
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Affiliation(s)
- Kai Tittmann
- Göttingen Center for Molecular Biosciences, Georg-August University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
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62
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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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63
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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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64
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Coupillaud P, Vignolle J, Mecerreyes D, Taton D. Post-polymerization modification and organocatalysis using reactive statistical poly(ionic liquid)-based copolymers. POLYMER 2014. [DOI: 10.1016/j.polymer.2014.02.043] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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65
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Berry MT, Castrejon D, Hein JE. Oxidative Esterification of Aldehydes Using Mesoionic 1,2,3-Triazolyl Carbene Organocatalysts. Org Lett 2014; 16:3676-9. [DOI: 10.1021/ol501458p] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Matthew T. Berry
- Department
of Chemistry and
Chemical Biology, University of California, 5200 North Lake Road, Merced, California 95343, United States
| | - Disnay Castrejon
- Department
of Chemistry and
Chemical Biology, University of California, 5200 North Lake Road, Merced, California 95343, United States
| | - Jason E. Hein
- Department
of Chemistry and
Chemical Biology, University of California, 5200 North Lake Road, Merced, California 95343, United States
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66
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Laali KK, Insuasty D, Abonia R, Insuasty B, Bunge SD. Novel quinoline–imidazolium adducts via the reaction of 2-oxoquinoline-3-carbaldehyde and quinoline-3-carbaldehydes with 1-butyl-3-methylimidazolium chloride [BMIM][Cl]. Tetrahedron Lett 2014. [DOI: 10.1016/j.tetlet.2014.05.094] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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67
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Zhao M, Yang H, Li MM, Chen J, Zhou L. N-Heterocyclic Carbene Catalyzed Intramolecular Acylation of Allylic Electrophiles. Org Lett 2014; 16:2904-7. [DOI: 10.1021/ol501046p] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Ming Zhao
- Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Department of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China
| | - Hui Yang
- Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Department of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China
| | - Miao-Miao Li
- Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Department of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China
| | - Jie Chen
- Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Department of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China
| | - Ling Zhou
- Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Department of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China
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68
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Martin D, Canac Y, Lavallo V, Bertrand G. Comparative Reactivity of Different Types of Stable Cyclic and Acyclic Mono- and Diamino Carbenes with Simple Organic Substrates. J Am Chem Soc 2014; 136:5023-30. [DOI: 10.1021/ja412981x] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- David Martin
- UCSD-CNRS Joint Research Laboratory
(UMI 3555), Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0343, United States
| | - Yves Canac
- UCSD-CNRS Joint Research Laboratory
(UMI 3555), Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0343, United States
- Laboratoire de Chimie
de Coordination, (CNRS, UPR 8241), 31077 Toulouse, France
| | - Vincent Lavallo
- UCSD-CNRS Joint Research Laboratory
(UMI 3555), Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0343, United States
- Department of Chemistry, University of California at Riverside, Riverside, California 92521, United States
| | - Guy Bertrand
- UCSD-CNRS Joint Research Laboratory
(UMI 3555), Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0343, United States
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69
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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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70
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Mahatthananchai J, Bode JW. On the mechanism of N-heterocyclic carbene-catalyzed reactions involving acyl azoliums. Acc Chem Res 2014; 47:696-707. [PMID: 24410291 DOI: 10.1021/ar400239v] [Citation(s) in RCA: 563] [Impact Index Per Article: 56.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Catalytic reactions promoted by N-heterocyclic carbenes (NHCs) have exploded in popularity since 2004 when several reports described new fundamental reactions that extended beyond the long-studied generation of acyl anion equivalents. These new NHC-catalyzed reactions allow chemists to generate unique reactive species from otherwise inert starting materials, all under simple, mild reaction conditions and with exceptional selectivities. In analogy to transition metal catalysis, the use of NHCs has introduced a new set of elementary steps that operate via discrete reactive species, including acyl anion, homoenolate, and enolate equivalents, usually generated by oxidation state reorganization ("redox neutral" reactions). Nearly all NHC-catalyzed reactions offer operationally simple reactions, proceed at room temperature without the need for stringent exclusion of air, and do not generate reaction byproducts. Variation of the catalyst or reaction conditions can profoundly influence reaction outcomes, and researchers can tune the desired selectivities through careful choice of NHC precursor and base. The catalytically generated homoenolate and enolate equivalents are nucleophilic species. In contrast, the catalytically generated acyl azolium and α,β-unsaturated acyl azoliums are electrophilic cationic species with unique and unprecedented chemistry. For example, when generated catalytically, these species transformed an α-functionalized aldehyde to an ester under redox neutral conditions without coupling reagents or waste. In addition to providing new approaches to catalytic esterifications, acyl azoliums offer unique reactivities that chemists can exploit for selective reactions. This Account focuses on the discovery and mechanistic investigation of the catalytic generation of acyl azoliums and α,β-unsaturated acyl azoliums. These chemical species are fascinating, and their catalytic generation is an important development. Studies of their unusual chemistry, however, date back to the intense investigation of thiamine-dependent enzymatic processes in the 1960s. Acyl azoliums are remarkably reactive in acylation chemistry and are unusually chemoselective. These two properties have led to a new wave of reactions such as redox esterification reaction (1) and the catalytic kinetic resolution of challenging substrates (i.e., 3). Our group and others have also developed methods to generate and exploit α,β-unsaturated acyl azoliums, which have facilitated new C-C bond-forming annulations, including a catalytic, enantioselective variant of the Claisen rearrangement (2). From essentially one class of catalysts, the N-mesityl derived triazolium salts, researchers can easily prepare highly enantioenriched dihydropyranones and dihydropyridinones. Although this field is now one of the most explored areas of enantioselective C-C bond forming reactions, many mechanistic details remained unsolved and in dispute. In this Account, we address the mechanistic inquiries about the characterization of the unsaturated acyl triazolium species and its kinetic profile under catalytically relevant conditions. We also provide explanations for the requirement and effect of the N-mesityl group in NHC catalysis based on detailed experimental data within given specific reactions or conditions. We hope that our studies provide a roadmap for catalyst design/selection and new reaction discovery based on a fundamental understanding of the mechanistic course of NHC reactions.
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Affiliation(s)
- Jessada Mahatthananchai
- Laboratorium für Organische Chemie, ETH−Zürich, Wolfgang Pauli Strasse 10, 8093 Zürich, Switzerland
| | - Jeffrey W. Bode
- Laboratorium für Organische Chemie, ETH−Zürich, Wolfgang Pauli Strasse 10, 8093 Zürich, Switzerland
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71
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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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72
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Hoshimoto Y. Capturing 2,2-Diamino Enols: A ^|^ldquo;Missing Link^|^rdquo; in Umpolung Reaction of Aldehydes by N-Heterocyclic Carbenes. J SYN ORG CHEM JPN 2014. [DOI: 10.5059/yukigoseikyokaishi.72.1158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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73
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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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74
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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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75
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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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76
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Kato T, Ota Y, Matsuoka SI, Takagi K, Suzuki M. Experimental mechanistic studies of the tail-to-tail dimerization of methyl methacrylate catalyzed by N-heterocyclic carbene. J Org Chem 2013; 78:8739-47. [PMID: 23941561 DOI: 10.1021/jo401477b] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
We and others have previously reported the intermolecular umpolung reactions of Michael acceptors catalyzed by an N-heterocyclic carbene (NHC). The representative tail-to-tail dimerization of methyl methacrylate (MMA) has now been intensively investigated, leading to the following conclusions: (1) The catalysis involves the deoxy-Breslow intermediate, which is quite stable and remains active after the catalysis. (2) Addition of the intermediate to MMA and the final catalyst elimination are the rate-limiting steps. Addition of the NHC to MMA and the proton transfers are relatively very rapid. (3) The two alkenyl protons of the first MMA undergo an intermolecular transfer to C3 and C5 of the dimer. (4) The initial proton transfer is intermolecular. (5) Compared with the benzoin condensation, noticeable differences in the kinetics, reversibility, and stability of the intermediates are observed.
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Affiliation(s)
- Terumasa Kato
- Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan
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77
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Sun H, Fang X, Chi YR, Li G. Theoretical Study of N-Heterocyclic Carbenes-Catalyzed Cascade Annulation of Benzodienones and Enals. Chirality 2013; 25:521-8. [DOI: 10.1002/chir.22157] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2012] [Revised: 12/16/2012] [Accepted: 12/21/2012] [Indexed: 11/08/2022]
Affiliation(s)
- Hui Sun
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics; Chinese Academy of Sciences; People's Republic of China
| | - Xinqiang Fang
- Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences; Nanyang Technological University; Singapore
| | - Yonggui Robin Chi
- Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences; Nanyang Technological University; Singapore
| | - Guohui Li
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics; Chinese Academy of Sciences; People's Republic of China
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78
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Möhlmann L, Ludwig S, Blechert S. NHC-catalysed highly selective aerobic oxidation of nonactivated aldehydes. Beilstein J Org Chem 2013; 9:602-7. [PMID: 23616801 PMCID: PMC3628286 DOI: 10.3762/bjoc.9.65] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Accepted: 02/26/2013] [Indexed: 11/23/2022] Open
Abstract
This publication describes a highly selective oxidation of aldehydes to the corresponding acids or esters. The reaction proceeds under metal-free conditions by using N-heterocyclic carbenes as organocatalysts in combination with environmentally friendly oxygen as the terminal oxidation agent.
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Affiliation(s)
- Lennart Möhlmann
- TU-Berlin - Berlin Institute of Technology, Institute of Chemistry, Straße des 17. Juni 115, 10623 Berlin, Germany. ; Tel:(+49)-30-314-22255
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79
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80
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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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81
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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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82
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83
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Fèvre M, Pinaud J, Gnanou Y, Vignolle J, Taton D. N-Heterocyclic carbenes (NHCs) as organocatalysts and structural components in metal-free polymer synthesis. Chem Soc Rev 2013; 42:2142-72. [PMID: 23288304 DOI: 10.1039/c2cs35383k] [Citation(s) in RCA: 399] [Impact Index Per Article: 36.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The chemistry of N-heterocyclic carbenes (NHCs) has witnessed tremendous development in the past two decades: NHCs have not only become versatile ligands for transition metals, but have also emerged as powerful organic catalysts in molecular chemistry and, more recently, in metal-free polymer synthesis. To understand the success of NHCs, this review first presents the electronic properties of NHCs, their main synthetic methods, their handling, and their reactivity. Their ability to activate key functional groups (e.g. aldehydes, esters, heterocycles, silyl ketene acetals, alcohols) is then discussed in the context of molecular chemistry. Focus has been placed on the activation of substrates finding analogies with monomers (e.g. bis-aldehydes, multi-isocyanates, cyclic esters, epoxides, N-carboxyanhydrides, etc.) and/or initiators (e.g. hydroxy- or trimethylsilyl-containing reagents) employed in such "organopolymerisation" reactions utilizing NHCs. A variety of metal-free polymers, including aliphatic polyesters and polyethers, poly(α-peptoid)s, poly(meth)acrylates, polyurethanes, or polysiloxanes can be obtained in this way. The last section covers the use of NHCs as structural components of the polymer chain. Indeed, NHC-based photoinitiators, chain transfer agents or functionalizing agents, as well as bifunctional NHC monomer substrates, can also serve for metal-free polymer synthesis.
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Affiliation(s)
- Maréva Fèvre
- Centre National de la Recherche Scientifique, Laboratoire de Chimie des Polymères Organiques, 16 avenue Pey-Berland, F-33607 Pessac cedex, France
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84
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Collett CJ, Massey RS, Maguire OR, Batsanov AS, O'Donoghue AC, Smith AD. Mechanistic insights into the triazolylidene-catalysed Stetter and benzoin reactions: role of the N-aryl substituent. Chem Sci 2013. [DOI: 10.1039/c2sc22137c] [Citation(s) in RCA: 125] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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85
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86
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Marchenko AP, Koidan HN, Zarudnitskii EV, Hurieva AN, Kirilchuk AA, Yurchenko AA, Biffis A, Kostyuk AN. Stable N-Phosphorylated 1,2,4-Triazol-5-ylidenes: Novel Ligands for Metal Complexes. Organometallics 2012. [DOI: 10.1021/om300872g] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Anatoliy P. Marchenko
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Str. 5, Kyiv-94,
02094 Ukraine
| | - Heorgiy N. Koidan
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Str. 5, Kyiv-94,
02094 Ukraine
| | - Evgeniy V. Zarudnitskii
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Str. 5, Kyiv-94,
02094 Ukraine
| | - Anastasiya N. Hurieva
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Str. 5, Kyiv-94,
02094 Ukraine
| | - Andrey A. Kirilchuk
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Str. 5, Kyiv-94,
02094 Ukraine
| | - Aleksandr A. Yurchenko
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Str. 5, Kyiv-94,
02094 Ukraine
| | - Andrea Biffis
- Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, I-35131 Padova, Italy
| | - Aleksandr N. Kostyuk
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Str. 5, Kyiv-94,
02094 Ukraine
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87
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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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88
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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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89
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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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90
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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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91
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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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92
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93
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Mayr H, Lakhdar S, Maji B, Ofial AR. A quantitative approach to nucleophilic organocatalysis. Beilstein J Org Chem 2012; 8:1458-78. [PMID: 23019481 PMCID: PMC3458771 DOI: 10.3762/bjoc.8.166] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Accepted: 07/31/2012] [Indexed: 12/23/2022] Open
Abstract
The key steps in most organocatalytic cyclizations are the reactions of electrophiles with nucleophiles. Their rates can be calculated by the linear free-energy relationship log k(20 °C) = s(N)(E + N), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the solvent-dependent nucleophilicity (N) and sensitivity (s(N)) parameters.Electrophilicity parameters in the range -10 < E < -5 were determined for iminium ions derived from cinnamaldehyde and common organocatalysts, such as pyrrolidines and imidazolidinones, by studying the rates of their reactions with reference nucleophiles. Iminium activated reactions of α,β-unsaturated aldehydes can, therefore, be expected to proceed with nucleophiles of 2 < N < 14, because such nucleophiles are strong enough to react with iminium ions but weak enough not to react with their precursor aldehydes. With the N parameters of enamines derived from phenylacetaldehyde and MacMillan's imidazolidinones one can rationalize why only strong electrophiles, such as stabilized carbenium ions (-8 < E < -2) or hexachlorocyclohexadienone (E = -6.75), are suitable electrophiles for enamine activated reactions with imidazolidinones. Several mechanistic controversies concerning iminium and enamine activated reactions could thus be settled by studying the reactivities of independently synthesized intermediates.Kinetic investigations of the reactions of N-heterocyclic carbenes (NHCs) with benzhydrylium ions showed that they have similar nucleophilicities to common organocatalysts (e.g., PPh(3), DMAP, DABCO) but are much stronger (100-200 kJ mol(-1)) Lewis bases. While structurally analogous imidazolylidenes and imidazolidinylidenes have comparable nucleophilicities and Lewis basicities, the corresponding deoxy Breslow intermediates differ dramatically in reactivity. The thousand-fold higher nucleophilicity of 2-benzylidene-imidazoline relative to 2-benzylidene-imidazolidine is explained by the gain of aromaticity during electrophilic additions to the imidazoline derivatives. O-Methylated Breslow intermediates are a hundred-fold less nucleophilic than deoxy Breslow intermediates.
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Affiliation(s)
- Herbert Mayr
- Department Chemie, Ludwig-Maximilians-Universität München, Butenandstr. 5-13 (Haus F), 81377 München, Germany
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94
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Allen SE, Mahatthananchai J, Bode JW, Kozlowski MC. Oxyanion steering and CH-π interactions as key elements in an N-heterocyclic carbene-catalyzed [4 + 2] cycloaddition. J Am Chem Soc 2012; 134:12098-103. [PMID: 22765294 PMCID: PMC3405918 DOI: 10.1021/ja302761d] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The N-heterocyclic carbene catalyzed [4 + 2] cycloaddition has been shown to give γ,δ-unsaturated δ-lactones in excellent enantio- and diastereoselectivity. However, preliminary computational studies of the geometry of the intermediate enolate rendered ambiguous both the origins of selectivity and the reaction pathway. Here, we show that a concerted, but highly asynchronous, Diels-Alder reaction occurs rather than the stepwise Michael-type or Claisen-type pathways. In addition, two crucial interactions are identified that enable high selectivity: an oxyanion-steering mechanism and a CH-π interaction. The calculations accurately predict the enantioselectivity of a number of N-heterocyclic carbene catalysts in the hetero-Diels-Alder reaction.
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Affiliation(s)
- Scott E. Allen
- Department of Chemistry, Roy and Diana Vagelos Laboratories, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | | | - Jeffrey W. Bode
- Laboratorium für Organische Chemie, ETH-Zürich, Zürich 8093, Switzerland
| | - Marisa C. Kozlowski
- Department of Chemistry, Roy and Diana Vagelos Laboratories, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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95
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Hollóczki O, Kelemen Z, Nyulászi L. On the organocatalytic activity of N-heterocyclic carbenes: role of sulfur in thiamine. J Org Chem 2012; 77:6014-22. [PMID: 22731396 DOI: 10.1021/jo300745e] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The reaction energy profiles of the benzoin condensation from three aldehydes catalyzed by imidazol-2-ylidene, triazol-3-ylidene, and thiazol-2-ylidene have been investigated computationally. The barriers for all steps of all investigated reactions have been found to be low enough to indicate the viability of the mechanism proposed by Breslow in the 1950s. The most remarkable difference in the catalytic cycles has been the increased stability of the Breslow intermediate in case of thiazol-2-ylidene (by ca. 10 kcal/mol) compared to the other two carbenes, which results in lower energy for the coupling of the second aldehyde molecule, thus, increasing the reversibility of the reaction. Since the analogous transketolase reaction, being involved in the carbohydrate metabolism of many organisms, requires an initial decoupling-a reverse benzoin condensation-this difference provides a reasonable explanation for the presence of a thiazolium ring in thiamine instead of the otherwise generally more available imidazole derivatives. The "resting intermediate" found by Berkessel and co-workers for a triazole-based catalyst was found more stable than the Breslow intermediate for all of the systems investigated. The (gas phase) proton affinities of several carbenes were compared, the relative trends being in agreement with the available (in aqueous solution) data. The hydrolytic ring-opening reaction of the thiazole-based carbene was shown to be different from that of imidazole-2-ylidenes.
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Affiliation(s)
- Oldamur Hollóczki
- Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Szt. Gellért tér 4., Budapest, H-1111, Hungary.
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96
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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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97
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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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98
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DiRocco DA, Oberg KM, Rovis T. Isolable analogues of the Breslow intermediate derived from chiral triazolylidene carbenes. J Am Chem Soc 2012; 134:6143-5. [PMID: 22455368 PMCID: PMC3336740 DOI: 10.1021/ja302031v] [Citation(s) in RCA: 125] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Since Breslow's initial report on the thiamine mode of action, the study of catalytic acyl carbanion processes has been an area of immense interest. With the advent of azolylidene catalysis, a plethora of reactivtiy has been harnessed, but the crucial nucleophilic intermediate proposed by Breslow had never been isolated or fully characterized. Herein, we report the isolation and full characterization of nitrogen analogues of the Breslow intermediate. Both stable and catalytically relevant, these species provide a model system for the study of acyl carbanion and homoenolate processes catalyzed by triazolylidene carbenes.
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Affiliation(s)
- Daniel A. DiRocco
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523
| | - Kevin M. Oberg
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523
| | - Tomislav Rovis
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523
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99
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Mahatthananchai J, Bode JW. The effect of the N-mesityl group in NHC-catalyzed reactions. Chem Sci 2012; 3:192-197. [PMID: 23687565 DOI: 10.1039/c1sc00397f] [Citation(s) in RCA: 182] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The majority of N-heterocyclic carbene catalyzed reactions of α-functionalized aldehydes, including annulations, oxidations, and redox reactions, occur more rapidly with N-mesityl substituted NHCs. In many cases, no reaction occurs with NHCs lacking ortho-substituted aromatics. By careful competition studies, catalyst analogue synthesis, mechanistic investigations, and consideration of the elementary steps in NHC-catalyzed reactions of enals, we have determined that the effect of the N-mesityl group is to render the initial addition of the NHC to the aldehyde irreversible, thereby accelerating the formation of the Breslow intermediate. These studies rationalize the experimentally observed catalyst preference for all classes of NHC-catalyzed reactions of aldehydes and provide a roadmap for catalyst selection and design.
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100
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Phippen CBW, Goldys AM, McErlean CSP. Stetter Reactions of Unsaturated 1-Acyl-1H-pyrroles. European J Org Chem 2011. [DOI: 10.1002/ejoc.201101151] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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