1
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Lorkowski J, Yorkgitis P, Serrato MR, Gembicky M, Pietraszuk C, Bertrand G, Jazzar R. Genuine carbene versus carbene-like reactivity. Angew Chem Int Ed Engl 2024; 63:e202401020. [PMID: 38632078 DOI: 10.1002/anie.202401020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2024] [Revised: 04/14/2024] [Accepted: 04/17/2024] [Indexed: 04/19/2024]
Abstract
Singlet carbenes are not always isolable and often even elude direct detection. When they escape observation, their formation can sometimes be evidenced by in situ trapping experiments. However, is carbene-like reactivity genuine evidence of carbene formation? Herein, using the first example of a spectroscopically characterized cyclic (amino)(aryl)carbene (CAArC), we cast doubt on the most common carbene trapping reactions as sufficient proof of carbene formation.
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Affiliation(s)
- Jan Lorkowski
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA-92093-0343, USA
| | - Patrick Yorkgitis
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA-92093-0343, USA
| | - Melinda R Serrato
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA-92093-0343, USA
| | - Milan Gembicky
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA-92093-0343, USA
| | - Cezary Pietraszuk
- Faculty of Chemistry, Adam Mickiewicz University, Poznań, Uniwersytetu Poznańskiego 8, 61-614, Poznań, Poland
| | - Guy Bertrand
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA-92093-0343, USA
| | - Rodolphe Jazzar
- UCSD-CNRS Joint Research Chemistry Laboratory (IRL 3555), Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA-92093-0343, USA
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2
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Mazars F, Zaragoza G, Delaude L. The facile alkylation and iodination of imidazol(in)ium salts in the presence of cesium carbonate. Chem Commun (Camb) 2023; 59:14528-14531. [PMID: 37942885 DOI: 10.1039/d3cc04971j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2023]
Abstract
The alkylation or iodination of imidazol(in)ium salts takes place readily in the presence of Cs2CO3. The procedure is very easy to implement and provides facile and straightforward access to a wealth of C2-substituted azolium salts. Furthermore, a C2α alkylation is also feasible, which extends the chemistry of NHCs and weak bases to their NHO analogues.
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Affiliation(s)
- François Mazars
- Laboratory of Catalysis, MolSys Research Unit, Université de Liège, Institut de Chimie Organique (B6a), Allée du six Août 13, Liège 4000, Belgium.
| | - Guillermo Zaragoza
- Unidade de Difracción de Raios X, RIAIDT, Universidade de Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, Spain
| | - Lionel Delaude
- Laboratory of Catalysis, MolSys Research Unit, Université de Liège, Institut de Chimie Organique (B6a), Allée du six Août 13, Liège 4000, Belgium.
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3
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Uranga J, Rabe von Pappenheim F, Tittmann K, Mata RA. Dynamic Protonation States Underlie Carbene Formation in ThDP-Dependent Enzymes: A Theoretical Study. J Phys Chem B 2023; 127. [PMID: 37748048 PMCID: PMC10688766 DOI: 10.1021/acs.jpcb.3c03137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 09/09/2023] [Indexed: 09/27/2023]
Abstract
The activation mechanism of thiamine diphosphate (ThDP) in enzymes has long been the subject of intense research and controversial discussion. Particularly contentious is the formation of a carbene intermediate, the first one observed in an enzyme. For the formation of the carbene to take place, both intramolecular and intermolecular proton transfer pathways have been proposed. However, the physiologically relevant pH of ThDP-dependent enzymes around neutrality does not seem to be suitable for the formation of such reactive chemical species. Herein, we investigate the general mechanism of activation of the ThDP cofactor in human transketolase (TKT), by means of electronic structure methods. We show that in the case of the human TKT, the carbene species is accessible through a pKa shift induced by the electrostatics of a neighboring histidine residue (H110), whose protonation state change modulates the pKa of ThDP and suppresses the latter by more than 6 pH units. Our findings highlight that ThDP enzymes activate the cofactor beyond simple geometric constraints and the canonical glutamate. Such observations in nature can pave the way for the design of biomimetic carbene catalysts and the engineering of tailored enzymatic carbenes.
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Affiliation(s)
- Jon Uranga
- Institute
of Physical Chemistry, Georg-August Universität
Göttingen, Tammannstraße 6, 37077 Göttingen, Germany
| | - Fabian Rabe von Pappenheim
- Department
of Molecular Enzymology, Göttingen Center of Molecular Biosciences, Georg-August Universität Göttingen, Julia-Lermonotowa-Weg 3, D-37077 Göttingen, Germany
| | - Kai Tittmann
- Department
of Molecular Enzymology, Göttingen Center of Molecular Biosciences, Georg-August Universität Göttingen, Julia-Lermonotowa-Weg 3, D-37077 Göttingen, Germany
- Department
of Physical Biochemistry, Max-Planck-Institute
for Multidisciplinary Natural Sciences, Am Faßberg 11, D-37077 Göttingen, Germany
| | - Ricardo A. Mata
- Institute
of Physical Chemistry, Georg-August Universität
Göttingen, Tammannstraße 6, 37077 Göttingen, Germany
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4
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De Risi C, Brandolese A, Di Carmine G, Ragno D, Massi A, Bortolini O. Oxidative N-Heterocyclic Carbene Catalysis. Chemistry 2023; 29:e202202467. [PMID: 36205918 PMCID: PMC10099058 DOI: 10.1002/chem.202202467] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Indexed: 11/05/2022]
Abstract
N-Heterocyclic carbene (NHC) catalysis is a by now consolidated organocatalytic platform for a number of synthetic (asymmetric) transformations via diverse reaction modes/intermediates. In addition to the typical umpolung processes involving acyl anion/homoenolate equivalent species, implementation of protocols under oxidative conditions greatly expands the possibilities of this methodology. Oxidative NHC-catalysis allows for oxidative and oxygenative transformations through specific manipulations of Breslow-type species depending upon the oxidant used (external oxidant or O2 /air), the derived NHC-bound intermediates paving the way to non-umpolung processes through activation of carbon atoms and heteroatoms. This review is intended to update the state of the art in oxidative NHC-catalyzed reactions that appeared in the literature from 2014 to present, with a strong focus to crucial intermediates and their mechanistic implications.
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Affiliation(s)
- Carmela De Risi
- Dipartimento di Scienze Chimiche, Farmaceutiche ed Agrarie, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Arianna Brandolese
- Dipartimento di Scienze dell'Ambiente e della Prevenzione, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Graziano Di Carmine
- Dipartimento di Scienze Chimiche, Farmaceutiche ed Agrarie, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Daniele Ragno
- Dipartimento di Scienze Chimiche, Farmaceutiche ed Agrarie, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Alessandro Massi
- Dipartimento di Scienze Chimiche, Farmaceutiche ed Agrarie, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
| | - Olga Bortolini
- Dipartimento di Scienze dell'Ambiente e della Prevenzione, Università di Ferrara, Via L. Borsari, 46, 44121, Ferrara, Italy
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5
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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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6
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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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7
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Direct Synthesis of Vinylene Carbonates from Aromatic Aldehydes. European J Org Chem 2022. [DOI: 10.1002/ejoc.202200153] [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]
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8
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Barnett C, Harper JB, Cole ML. Correlating Electronic Properties of
N
‐Heterocyclic Carbenes with Structure, and the Implications of Using Different Probes. ChemistrySelect 2022. [DOI: 10.1002/slct.202104348] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Christopher Barnett
- School of Chemistry University of New South Wales, UNSW Sydney NSW 2052 Australia
- Current address: School of Chemistry The University of Sydney Sydney NSW 2006 Australia
| | - Jason B. Harper
- School of Chemistry University of New South Wales, UNSW Sydney NSW 2052 Australia
| | - Marcus L. Cole
- School of Chemistry University of New South Wales, UNSW Sydney NSW 2052 Australia
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9
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Belen’kii LI, Gazieva GA, Evdokimenkova YB, Soboleva NO. The literature of heterocyclic chemistry, Part XX, 2020. ADVANCES IN HETEROCYCLIC CHEMISTRY 2022. [DOI: 10.1016/bs.aihch.2022.10.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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10
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Cho J, Shin J, Kang M, Verwilst P, Lim C, Yoo H, Kim JG, Zhang X, Hong CS, Kim JS, Kim S. Calix[ n]triazolium based turn-on fluorescent sensing ensemble for selective adenosine monophosphate (AMP) detection. Chem Commun (Camb) 2021; 57:12139-12142. [PMID: 34724524 DOI: 10.1039/d1cc04950j] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A novel calix[n]triazolium was synthesized and exhibited excellent selectivity for AMP. The binding between calix[n]triazolium and chromenolate anions forms a non-fluorescent complex and the resulting supramolecular ensemble selectively detects AMP in water and induces "turn-on" fluorescence. The sensing platform is the first macrocyclic system to discriminate AMP from ADP and ATP through fluorescence changes.
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Affiliation(s)
- Jihee Cho
- College of Pharmacy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea.
| | - Jinwoo Shin
- Department of Chemistry, Korea University, Seoul 02841, Korea.
| | - Minjung Kang
- Department of Chemistry, Korea University, Seoul 02841, Korea.
| | - Peter Verwilst
- KU Leuven, Rega Institute for Medical Research, Medicinal Chemistry, Leuven 3000, Belgium
| | - Changhyun Lim
- College of Pharmacy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea.
| | - Hanbin Yoo
- College of Pharmacy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea.
| | - Jeung Gon Kim
- Department of Chemistry and Research Institute of Physics and Chemistry, Jeonbuk National University, Jeonju 54896, Korea
| | - Xingcai Zhang
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.,School of Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Chang Seop Hong
- Department of Chemistry, Korea University, Seoul 02841, Korea.
| | - Jong Seung Kim
- Department of Chemistry, Korea University, Seoul 02841, Korea.
| | - Sanghee Kim
- College of Pharmacy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea.
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11
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Schotten C, Bourne RA, Kapur N, Nguyen BN, Willans CE. Electrochemical Generation of
N
‐Heterocyclic Carbenes for Use in Synthesis and Catalysis. Adv Synth Catal 2021. [DOI: 10.1002/adsc.202100264] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Affiliation(s)
| | - Richard A. Bourne
- School of Chemical and Process Engineering University of Leeds Leeds LS2 9JT UK
| | - Nikil Kapur
- School of Mechanical Engineering University of Leeds Leeds LS2 9JT UK
| | - Bao N. Nguyen
- School of Chemistry University of Leeds Leeds LS2 9JT UK
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12
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Mazars F, Hrubaru M, Tumanov N, Wouters J, Delaude L. Synthesis of Azolium‐2‐dithiocarboxylate Zwitterions under Mild, Aerobic Conditions. European J Org Chem 2021. [DOI: 10.1002/ejoc.202100274] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- François Mazars
- Laboratory of Catalysis MolSys Research Unit Université de Liège Institut de Chimie Organique (B6a) Allée du six Août 13 4000 Liège Belgium
| | - Madalina Hrubaru
- Center for Organic Chemistry “Costin D. Nenitescu” Romanian Academy Spl Independentei Bucureşti, 202B 060023 Bucharest Romania
| | - Nikolay Tumanov
- Department of Chemistry Université de Namur Rue de Bruxelles 61 5000 Namur Belgium
| | - Johan Wouters
- Department of Chemistry Université de Namur Rue de Bruxelles 61 5000 Namur Belgium
| | - Lionel Delaude
- Laboratory of Catalysis MolSys Research Unit Université de Liège Institut de Chimie Organique (B6a) Allée du six Août 13 4000 Liège Belgium
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13
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Zhang D, Jarava-Barrera C, Bontemps S. Selective Reductive Dimerization of CO2 into Glycolaldehyde. ACS Catal 2021. [DOI: 10.1021/acscatal.1c00412] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- Dan Zhang
- LCC-CNRS, Université de Toulouse, CNRS, 205 Route de Narbonne, Toulouse 31077, Cedex 04, France
| | - Carlos Jarava-Barrera
- LCC-CNRS, Université de Toulouse, CNRS, 205 Route de Narbonne, Toulouse 31077, Cedex 04, France
| | - Sébastien Bontemps
- LCC-CNRS, Université de Toulouse, CNRS, 205 Route de Narbonne, Toulouse 31077, Cedex 04, France
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14
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Zhang Q, Das DK, Yang S, Fu Y, Fang X. Mechanistic Studies on N-Heterocyclic Carbene-Catalyzed Umpolung of β,γ-Unsaturated α-Diketones. J Org Chem 2021; 86:4432-4439. [PMID: 33719444 DOI: 10.1021/acs.joc.0c02565] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The mechanism of N-heterocyclic carbene-catalyzed umpolung of β,γ-unsaturated α-diketone was studied using both density functional theory (DFT) calculations and experimental methods. In contrast to the originally proposed mechanism, the calculations revealed a more complicated process involving both nucleophilic O-acylated homoenolate and electrophilic α,β-unsaturated acyl azolium intermediates. The experimental studies confirmed the existence of the aforementioned two key intermediates. A revised mechanism has been proposed to demonstrate the detailed mechanistic insights into the product formation.
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Affiliation(s)
- Qi Zhang
- Institute of Industry and Equipment Technology, Hefei University of Technology, Hefei 230009, China
| | - Deb Kumar Das
- State Key Laboratory of Structural Chemistry, and Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Center for Excellence in Molecular Synthesis, Fujian Institute of Research on the Structure of Matter, University of Chinese Academy of Sciences, Fuzhou 350100, China
| | - Shuang Yang
- State Key Laboratory of Structural Chemistry, and Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Center for Excellence in Molecular Synthesis, Fujian Institute of Research on the Structure of Matter, University of Chinese Academy of Sciences, Fuzhou 350100, China
| | - Yao Fu
- Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Xinqiang Fang
- State Key Laboratory of Structural Chemistry, and Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Center for Excellence in Molecular Synthesis, Fujian Institute of Research on the Structure of Matter, University of Chinese Academy of Sciences, Fuzhou 350100, China
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15
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Vetica F, Bortolami M, Petrucci R, Rocco D, Feroci M. Electrogenerated NHCs in Organic Synthesis: Ionic Liquids vs Organic Solvents Effects. CHEM REC 2021; 21:2130-2147. [PMID: 33507627 DOI: 10.1002/tcr.202000178] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 01/08/2021] [Indexed: 12/14/2022]
Abstract
In the last twenty years, N-heterocyclic carbenes (NHCs) have been extensively studied for their application as organocatalysts in stereoselective synthesis as well as ligands for transition metals-promoted synthetic methodologies. Derived mainly from azolium salts, NHCs have demonstrated exceptional versatility in their generation usually performed by deprotonation or reduction (chemical or electrochemical). In particular, the generation of NHC under electrochemical conditions, starting from azolium-based ionic liquids, has proven to be a successful green approach and demonstrated wide applicability in organic synthesis. In this Personal Account, the application of electrogenerated NHCs in organic synthesis will be discussed, with a particular attention to the different reactivity in ionic liquids compared to classical organic solvents.
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Affiliation(s)
- Fabrizio Vetica
- Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy
| | - Martina Bortolami
- Department of Basic and Applied Sciences for Engineering (SBAI), Sapienza University of Rome, Via Castro Laurenziano 7, 00161, Rome, Italy
| | - Rita Petrucci
- Department of Basic and Applied Sciences for Engineering (SBAI), Sapienza University of Rome, Via Castro Laurenziano 7, 00161, Rome, Italy
| | - Daniele Rocco
- Department of Basic and Applied Sciences for Engineering (SBAI), Sapienza University of Rome, Via Castro Laurenziano 7, 00161, Rome, Italy
| | - Marta Feroci
- Department of Basic and Applied Sciences for Engineering (SBAI), Sapienza University of Rome, Via Castro Laurenziano 7, 00161, Rome, Italy
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16
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Kaur BP, Kaur J, Chimni SS. Arenesulfonyl indole: new precursor for diversification of C-3 functionalized indoles. RSC Adv 2021; 11:2126-2140. [PMID: 35424187 PMCID: PMC8693840 DOI: 10.1039/d0ra09133b] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 12/16/2020] [Indexed: 12/11/2022] Open
Abstract
Arenesulfonyl indoles, bearing a good leaving group, are effective precursors for vinylogous imine intermediates which are generated in situ under basic conditions. This intermediate can readily react with other nucleophilic reagents to obtain C-3 substituted indole derivatives. In the last few years, a plethora of exciting synthetic applications of this substrate have been exploited. The stability of arylsulfonyl-containing substrates, mild reaction conditions, and the large variety of nucleophiles involved in these procedures are the key to their success in organic synthesis.
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Affiliation(s)
- Banni Preet Kaur
- Department of Chemistry, U.G.C. Centre of Advance Study-II, Guru Nanak Dev University Amritsar Punjab India
| | - Jasneet Kaur
- Post-Graduate Department of Chemistry, Khalsa College Amritsar Punjab India
| | - Swapandeep Singh Chimni
- Department of Chemistry, U.G.C. Centre of Advance Study-II, Guru Nanak Dev University Amritsar Punjab India
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17
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Bugaenko DI, Yurovskaya MA, Karchava AV. Reaction of Pyridine‐
N
‐Oxides with Tertiary sp
2
‐
N
‐Nucleophiles: An Efficient Synthesis of Precursors for
N
‐(Pyrid‐2‐yl)‐Substituted
N
‐Heterocyclic Carbenes. Adv Synth Catal 2020. [DOI: 10.1002/adsc.202001063] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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18
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Kinney ZJ, Rheingold AL, Protasiewicz JD. Preferential N-H⋯:C[double bond splayed right] hydrogen bonding involving ditopic NH-containing systems and N-heterocyclic carbenes. RSC Adv 2020; 10:42164-42171. [PMID: 35516763 PMCID: PMC9057831 DOI: 10.1039/d0ra08490e] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 11/05/2020] [Indexed: 11/21/2022] Open
Abstract
Hydrogen bonding plays a critical role in maintaining order and structure in complex biological and synthetic systems. N-heterocyclic carbenes (NHCs) represent one of the most versatile tools in the synthetic chemistry toolbox, yet their potential as neutral carbon hydrogen bond acceptors remains underexplored. This report investigates this capability in a strategic manner, wherein carbene-based hydrogen bonding can be assessed by use of ditopic NH-containing molecules. N-H bonds are unique as there are three established reaction modes with carbenes: non-traditional hydrogen bonding adducts (X-H⋯:C[double bond splayed right]), salts arising from proton transfer ([H-C[double bond splayed right]]+[X]-), or amines from insertion of the carbene into the N-H bond. Yet, there are no established rules to predict product distributions or the strength of these associations. Here we seek to correlate the hydrogen bond strength of symmetric and asymmetric ditopic secondary amines with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr, a representative NHC). In symmetric and asymmetric ditopic amine adducts both the solid-state (hydrogen bond lengths, NHC interior angles) and solution-state (1H Δδ of NH signals, 13C signals of carbenic carbon) can be related to the pK a of the parent amine.
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Affiliation(s)
- Zacharias J Kinney
- Department of Chemistry, Case Western Reserve University Cleveland Ohio 44106 USA
| | - Arnold L Rheingold
- Department of Chemistry and Biochemistry, University of California La Jolla San Diego California 92093 USA
| | - John D Protasiewicz
- Department of Chemistry, Case Western Reserve University Cleveland Ohio 44106 USA
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19
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N-PEGylated Thiazolium Salt: A Green and Reusable Homogenous Organocatalyst for the Synthesis of Benzoins and Acyloins. Catal Letters 2020. [DOI: 10.1007/s10562-020-03417-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Gehrke S, Hollóczki O. N-Heterocyclic Carbene Organocatalysis: With or Without Carbenes? Chemistry 2020; 26:10140-10151. [PMID: 32608090 PMCID: PMC7496998 DOI: 10.1002/chem.202002656] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 06/26/2020] [Indexed: 11/18/2022]
Abstract
In this work the mechanism of the aldehyde umpolung reactions, catalyzed by azolium cations in the presence of bases, was studied through computational methods. Next to the mechanism established by Breslow in the 1950s that takes effect through the formation of a free carbene, we have suggested that these processes can follow a concerted asynchronous path, in which the azolium cation directly reacts with the substrate, avoiding the formation of the carbene intermediate. We hereby show that substituting the azolium cation, and varying the base or the substrate do not affect the preference for the concerted reaction mechanism. The concerted path was found to exhibit low barriers also for the reactions of thiamine with model substrates, showing that this path might have biological relevance. The dominance of the concerted mechanism can be explained through the specific structure of the key transition state, avoiding the liberation of the highly reactive, and thus unstable carbene lone pair, whereas activating the substrate through hydrogen-bonding interactions. Polar and hydrogen-bonding solvents, as well as the presence of the counterions of the azolium salts facilitate the reaction through carbenes, bringing the barriers of the two reaction mechanisms closer, in many cases making the concerted path less favorable. Thus, our data show that by choosing the exact components in a reaction, the mechanism can be switched to occur with or without carbenes.
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Affiliation(s)
- Sascha Gehrke
- Mulliken Center for Theoretical ChemistryUniversity of BonnBeringstr. 4+653115BonnGermany
| | - Oldamur Hollóczki
- Mulliken Center for Theoretical ChemistryUniversity of BonnBeringstr. 4+653115BonnGermany
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Blasius J, Elfgen R, Hollóczki O, Kirchner B. Glucose in dry and moist ionic liquid: vibrational circular dichroism, IR, and possible mechanisms. Phys Chem Chem Phys 2020; 22:10726-10737. [PMID: 32150178 DOI: 10.1039/c9cp06798a] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ionic liquids and their mixtures with water show remarkable features in cellulose processing. For this reason, understanding the behavior of carbohydrates in ionic liquids is important. In the present study, we investigated three d-glucose isomers (α, β and open-chain) in 1-ethyl-3-methylimidazolium acetate in the presence and absence of water, through ab initio molecular dynamics simulations. In the complex hydrogen bonding network of these mixtures, the most interesting observation is that upon water addition every hydrogen bond elongates, except the glucose-glucose hydrogen bond for the open-chain and the α-form which shortens, clearly showing the beginning of the crystallization process. The ring glucose rearranges from on-top to in-plane and the open form changes from a coiled to a more linear arrangement when adding water which explains the contradiction that the center of mass distances of the glucose molecules with other glucose molecules grow while the hydrogen bonds shorten. The appearance of coiled open forms indicates that the previously suggested isomerization between these forms is possible and might play a role in the solubility of the related carbohydrates. The calculated IR and VCD spectra reveal insight into the intermolecular interactions, with good to excellent agreements with experimental spectra. Investigating the role of the cation, distances between the acidic carbon atom of the cation and the glucose carbon atom where ring closure and opening occurs are found, which are way shorter than dispersion-like interactions between aliphatic hydrocarbons.
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Affiliation(s)
- Jan Blasius
- Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstraße 4 + 6, D-53115 Bonn, Germany.
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Hollóczki O. The Mechanism of N-Heterocyclic Carbene Organocatalysis through a Magnifying Glass. Chemistry 2020; 26:4885-4894. [PMID: 31797448 PMCID: PMC7187225 DOI: 10.1002/chem.201903021] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Indexed: 11/11/2022]
Abstract
The term "N-Heterocyclic carbene organocatalysis" is often invoked in organic synthesis for reactions that are catalyzed by different azolium salts in the presence of bases. Although the mechanism of these reactions is considered today evident, a closer look into the details that have been collected throughout the last century reveals that there are many open questions and even contradictions in the field. Emerging new theoretical and experimental results offer solutions to these problems, because they show that through considering alternative reaction mechanisms a more consistent picture on the catalytic process can be obtained. These novel perspectives will be able to extend the scope of the reactions that we call today N-heterocyclic carbene organocatalysis.
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Affiliation(s)
- Oldamur Hollóczki
- Mulliken Center for Theoretical ChemistryUniversity of BonnBeringstrasse 4+653115BonnGermany
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