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Biremond T, Riomet M, Jubault P, Poisson T. Photocatalytic and Electrochemical Borylation and Silylation Reactions. CHEM REC 2023; 23:e202300172. [PMID: 37358334 DOI: 10.1002/tcr.202300172] [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: 05/10/2023] [Revised: 06/05/2023] [Indexed: 06/27/2023]
Abstract
Due to their high versatility borylated and silylated compounds are inevitable synthons for organic chemists. To escape the classical hydroboration/hydrosilylation paradigm, chemists turned their attention to more modern and green methods such as photoredox chemistry and electrosynthesis. This account focuses on novel methods for the generation of boryl and silyl radicals to forge C-B and C-Si bonds from our group.
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Affiliation(s)
- Tony Biremond
- Normandie Univ., INSA Rouen, UNIROUEN, CNRS, COBRA (UMR 6014), 76000, Rouen, France
| | - Margaux Riomet
- Normandie Univ., INSA Rouen, UNIROUEN, CNRS, COBRA (UMR 6014), 76000, Rouen, France
| | - Philippe Jubault
- Normandie Univ., INSA Rouen, UNIROUEN, CNRS, COBRA (UMR 6014), 76000, Rouen, France
| | - Thomas Poisson
- Normandie Univ., INSA Rouen, UNIROUEN, CNRS, COBRA (UMR 6014), 76000, Rouen, France
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2
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Constantin T, Górski B, Tilby MJ, Chelli S, Juliá F, Llaveria J, Gillen KJ, Zipse H, Lakhdar S, Leonori D. Halogen-atom and group transfer reactivity enabled by hydrogen tunneling. Science 2022; 377:1323-1328. [DOI: 10.1126/science.abq8663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The generation of carbon radicals by halogen-atom and group transfer reactions is generally achieved using tin and silicon reagents that maximize the interplay of enthalpic (thermodynamic) and polar (kinetic) effects. In this work, we demonstrate a distinct reactivity mode enabled by quantum mechanical tunneling that uses the cyclohexadiene derivative γ-terpinene as the abstractor under mild photochemical conditions. This protocol activates alkyl and aryl halides as well as several alcohol and thiol derivatives. Experimental and computational studies unveiled a noncanonical pathway whereby a cyclohexadienyl radical undergoes concerted aromatization and halogen-atom or group abstraction through the reactivity of an effective H atom. This activation mechanism is seemingly thermodynamically and kinetically unfavorable but is rendered feasible through quantum tunneling.
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Affiliation(s)
| | - Bartosz Górski
- Department of Chemistry, University of Manchester, Manchester M13 9PL, UK
| | - Michael J. Tilby
- Department of Chemistry, University of Manchester, Manchester M13 9PL, UK
| | - Saloua Chelli
- CNRS/Université Toulouse III—Paul Sabatier, Laboratoire Hétérochimie Fondamentale et Appliquée, LHFA UMR 5069, 31062 Toulouse Cedex 09, France
| | - Fabio Juliá
- Department of Chemistry, University of Manchester, Manchester M13 9PL, UK
| | - Josep Llaveria
- Global Discovery Chemistry, Therapeutics Discovery, Janssen Research & Development, Janssen-Cilag S.A., 45007 Toledo, Spain
| | - Kevin J. Gillen
- LifeArc, Accelerator Building, Open Innovation Campus, Stevenage SG1 2FX, UK
| | - Hendrik Zipse
- Department Chemie, LMU München, D-81377 München, Germany
| | - Sami Lakhdar
- CNRS/Université Toulouse III—Paul Sabatier, Laboratoire Hétérochimie Fondamentale et Appliquée, LHFA UMR 5069, 31062 Toulouse Cedex 09, France
| | - Daniele Leonori
- Institute of Organic Chemistry, RWTH Aachen University, 52056 Aachen, Germany
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3
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Wang T, Chen Y, Chen N, Xu J, Yang Z. Iridium-catalyzed highly stereoselective deoxygenation of tertiary cycloalkanols: stereoelectronic insights and synthetic applications. Org Biomol Chem 2021; 19:9004-9011. [PMID: 34607335 DOI: 10.1039/d1ob01690c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Excellent and unique diastereoselectivity is observed in the iridium-catalyzed deoxygenation of tertiary cyclohexanols and cyclopentanols. The substituent effect on the diastereoselectivity and detailed control models are analyzed case by case, using tertiary monocyclic and polycyclic cyclohexanols, bicyclic bridged cycloalkanols, and cyclopentanols as the model substrates. The selectivity is decided by the steric environment of the carbocation intermediates and is independent of the catalyst loading. Stereoelectronically, the iridium hydride approaches the carbocation in directions perpendicular to the carbocation plane. The sterically large iridium hydride delivers its hydride in the sterically least hindered direction to the carbocation. The deoxygenation has found important applications in the stereospecific arylations of sterically complex compounds. Our deoxygenation is stereochemically very different from the coupling reactions and can be used to specifically synthesize stereoisomers that are not available via cross-couplings.
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Affiliation(s)
- Tingting Wang
- Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
| | - Yang Chen
- Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
| | - Ning Chen
- Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
| | - Jiaxi Xu
- Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
| | - Zhanhui Yang
- Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
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5
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Yu X, Lübbesmeyer M, Studer A. Oligosilanes as Silyl Radical Precursors through Oxidative Si−Si Bond Cleavage Using Redox Catalysis. Angew Chem Int Ed Engl 2020; 60:675-679. [DOI: 10.1002/anie.202011738] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 09/14/2020] [Indexed: 12/30/2022]
Affiliation(s)
- Xiaoye Yu
- Organisch-Chemisches Institut Westfälische Wilhelms-Universität Corrensstrasse 40 48149 Münster Germany
| | - Maximilian Lübbesmeyer
- Organisch-Chemisches Institut Westfälische Wilhelms-Universität Corrensstrasse 40 48149 Münster Germany
| | - Armido Studer
- Organisch-Chemisches Institut Westfälische Wilhelms-Universität Corrensstrasse 40 48149 Münster Germany
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6
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Yu X, Lübbesmeyer M, Studer A. Oligosilanes as Silyl Radical Precursors through Oxidative Si−Si Bond Cleavage Using Redox Catalysis. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202011738] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Xiaoye Yu
- Organisch-Chemisches Institut Westfälische Wilhelms-Universität Corrensstrasse 40 48149 Münster Germany
| | - Maximilian Lübbesmeyer
- Organisch-Chemisches Institut Westfälische Wilhelms-Universität Corrensstrasse 40 48149 Münster Germany
| | - Armido Studer
- Organisch-Chemisches Institut Westfälische Wilhelms-Universität Corrensstrasse 40 48149 Münster Germany
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7
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Li D, Ma TK, Scott RJ, Wilden JD. Electrochemical radical reactions of alkyl iodides: a highly efficient, clean, green alternative to tin reagents. Chem Sci 2020; 11:5333-5338. [PMID: 34122992 PMCID: PMC8159374 DOI: 10.1039/d0sc01694b] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
An electrochemical ‘redox-relay’ system has been developed which allows the generation of C-centered radicals. Intermolecular ‘tin-like’ radical reactions can subsequently be conducted under the most benign of conditions. The yields and efficiency of the processes are competitive and even superior in most cases to comparable conditions with tributyltin hydride. The use of air and electricity as the promotor (instead of a tin or other reagent) combined with the aqueous reaction media make this a clean and ‘green’ alternative to these classic C–C bond forming processes. A ‘green’ and high-yielding electrochemical method for performing tin-free, intermolecular radical reactions (the Giese reaction) has been developed.![]()
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Affiliation(s)
- Diyuan Li
- Department of Chemistry, University College London 20 Gordon Street London WC1H 0AJ UK
| | - Tsz-Kan Ma
- Department of Chemistry, University College London 20 Gordon Street London WC1H 0AJ UK
| | - Reuben J Scott
- Department of Chemistry, University College London 20 Gordon Street London WC1H 0AJ UK
| | - Jonathan D Wilden
- Department of Chemistry, University College London 20 Gordon Street London WC1H 0AJ UK
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8
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Sato R, Okamoto R, Ishizuka T, Nakayama A, Karanjit S, Namba K. Microwave-assisted Tertiary Carbon Radical Reaction for Construction of Quaternary Carbon Center. CHEM LETT 2019. [DOI: 10.1246/cl.190040] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Ryota Sato
- Graduate School of Pharmaceutical Science and Research Cluster on “Innovative Chemical Sensing”, Tokushima University, Tokushima 770-8505, Japan
| | - Ryuji Okamoto
- Graduate School of Pharmaceutical Science and Research Cluster on “Innovative Chemical Sensing”, Tokushima University, Tokushima 770-8505, Japan
| | - Takumi Ishizuka
- Graduate School of Pharmaceutical Science and Research Cluster on “Innovative Chemical Sensing”, Tokushima University, Tokushima 770-8505, Japan
| | - Atsushi Nakayama
- Graduate School of Pharmaceutical Science and Research Cluster on “Innovative Chemical Sensing”, Tokushima University, Tokushima 770-8505, Japan
| | - Sangita Karanjit
- Graduate School of Pharmaceutical Science and Research Cluster on “Innovative Chemical Sensing”, Tokushima University, Tokushima 770-8505, Japan
| | - Kosuke Namba
- Graduate School of Pharmaceutical Science and Research Cluster on “Innovative Chemical Sensing”, Tokushima University, Tokushima 770-8505, Japan
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9
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Deng W, Ye C, Li Y, Li D, Bao H. Iron-Catalyzed Oxyalkylation of Terminal Alkynes with Alkyl Iodides. Org Lett 2018; 21:261-265. [PMID: 30582704 DOI: 10.1021/acs.orglett.8b03689] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A general oxyalkylation of terminal alkynes enabled by iron catalysis has been developed. Primary and secondary alkyl iodides acted as the alkylating reagents and afforded a range of α-alkylated ketones under mild reaction conditions. Acetyl tert-butyl peroxide (TBPA) was used as the radical relay precursor, providing the initiated methyl radical to start the radical relay process. Preliminary mechanistic studies were conducted, and late-stage functionalizations of natural product derivatives were performed.
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Affiliation(s)
- Weili Deng
- Key Laboratory of Innate Immune Biology of Fujian Province, Biomedical Research Center of South China, College of Life Sciences , Fujian Normal University , 1 Keji Road , Fuzhou 350117 , P. R. China
| | - Changqing Ye
- Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, State Key Laboratory of Structural Chemistry, Center for Excellence in Molecular Synthesis , Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences , 155 Yangqiao Road West , Fuzhou , Fujian 350002 , P. R. of China
| | - Yajun Li
- Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, State Key Laboratory of Structural Chemistry, Center for Excellence in Molecular Synthesis , Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences , 155 Yangqiao Road West , Fuzhou , Fujian 350002 , P. R. of China
| | - Daliang Li
- Key Laboratory of Innate Immune Biology of Fujian Province, Biomedical Research Center of South China, College of Life Sciences , Fujian Normal University , 1 Keji Road , Fuzhou 350117 , P. R. China
| | - Hongli Bao
- Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, State Key Laboratory of Structural Chemistry, Center for Excellence in Molecular Synthesis , Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences , 155 Yangqiao Road West , Fuzhou , Fujian 350002 , P. R. of China
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10
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Huang MH, Hao WJ, Jiang B. Recent Advances in Radical-Enabled Bicyclization and Annulation/1,n
-Bifunctionalization Reactions. Chem Asian J 2018; 13:2958-2977. [DOI: 10.1002/asia.201801119] [Citation(s) in RCA: 107] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Indexed: 11/06/2022]
Affiliation(s)
- Min-Hua Huang
- School of Chemistry & Materials Science; Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials; Jiangsu Normal University; Xuzhou 221116 P. R. China
- Biotechnology and Pharmaceutical Engineering; Nanjing Tech University; Nanjing 210009, Jiangsu P. R. China
| | - Wen-Juan Hao
- School of Chemistry & Materials Science; Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials; Jiangsu Normal University; Xuzhou 221116 P. R. China
| | - Bo Jiang
- School of Chemistry & Materials Science; Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials; Jiangsu Normal University; Xuzhou 221116 P. R. China
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11
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Bowry VW, Chatgilialoglu C. Radical Arene Addition vs Radical Reduction: Why Organometal Hydride Chain Reactions Stop and How To Make Them Go. J Org Chem 2018; 83:10037-10050. [PMID: 30028610 DOI: 10.1021/acs.joc.8b01387] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nonideal kinetic chain analysis was used to examine the kinetic limitations of free-radical synthesis. Homolytic aromatic substitution (HAS: ArH + R• → ArR + H•) occurs in a chain-terminating side reaction to the tributyltin hydride ( SnH) reduction chain (RX + SnH + ( i•)cat. → RH + SnX). Kinetic modeling of premixed and slow reagent addition reactions have clarified the mechanisms of SM HAS, with the azo initiator ( iNN i) acting not only as radical source but also (as an H• acceptor) as the redox catalyst for aromatization, and/or as a postaddition oxidant. Refractory halides and other hitherto baffling anomalies may arise from the build up of ipso (rather than ortho)-cycloadduct radicals in the steady-state radical population. The implications of these findings for "tin-free" radical chains (and emerging photoredox methods) are considered via historical and recent examples of the effects of chain-degrading radical transfer (to substrate, product, solvent, initiator, and/or reagent ligands) on the reagent's chain.
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Affiliation(s)
- Vincent W Bowry
- ISOF, Consiglio Nazionale delle Ricerche , Via P. Gobetti 101 , Bologna 40129 , Italy
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12
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Yang S, Tang W, Yang Z, Xu J. Iridium-Catalyzed Highly Efficient and Site-Selective Deoxygenation of Alcohols. ACS Catal 2018. [DOI: 10.1021/acscatal.8b02495] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Shiyi Yang
- State Key Laboratory of Chemical Resource Engineering, College of Science, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China
| | - Weiping Tang
- School of Pharmacy, University of Wisconsin—Madison, 777 Highland Avenue, Madison, Wisconsin 53705, United States
- Department of Chemistry, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
| | - Zhanhui Yang
- State Key Laboratory of Chemical Resource Engineering, College of Science, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China
| | - Jiaxi Xu
- State Key Laboratory of Chemical Resource Engineering, College of Science, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China
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13
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Jouha J, Khouili M, Hiebel MA, Guillaumet G, Suzenet F. Room temperature dehalogenation of (hetero)aryl halides with magnesium/methanol. Tetrahedron Lett 2018. [DOI: 10.1016/j.tetlet.2018.07.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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14
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Lubrin NCM, Vlasceanu A, Frandsen BN, Skov AB, Kilde MD, Mikkelsen KV, Nielsen MB. Dialkylated Dihydroazulene and Vinylheptafulvene Derivatives - Synthesis and Switching Properties. European J Org Chem 2017. [DOI: 10.1002/ejoc.201700446] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Nickie C. M. Lubrin
- Department of Chemistry and Center for Exploitation of Solar Energy; University of Copenhagen; Universitetsparken 5 2100 Copenhagen Ø Denmark
| | - Alexandru Vlasceanu
- Department of Chemistry and Center for Exploitation of Solar Energy; University of Copenhagen; Universitetsparken 5 2100 Copenhagen Ø Denmark
| | - Benjamin N. Frandsen
- Department of Chemistry and Center for Exploitation of Solar Energy; University of Copenhagen; Universitetsparken 5 2100 Copenhagen Ø Denmark
| | - Anders B. Skov
- Department of Chemistry and Center for Exploitation of Solar Energy; University of Copenhagen; Universitetsparken 5 2100 Copenhagen Ø Denmark
| | - Martin Drøhse Kilde
- Department of Chemistry and Center for Exploitation of Solar Energy; University of Copenhagen; Universitetsparken 5 2100 Copenhagen Ø Denmark
| | - Kurt V. Mikkelsen
- Department of Chemistry and Center for Exploitation of Solar Energy; University of Copenhagen; Universitetsparken 5 2100 Copenhagen Ø Denmark
| | - Mogens Brøndsted Nielsen
- Department of Chemistry and Center for Exploitation of Solar Energy; University of Copenhagen; Universitetsparken 5 2100 Copenhagen Ø Denmark
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15
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Xuan J, Studer A. Radical cascade cyclization of 1,n-enynes and diynes for the synthesis of carbocycles and heterocycles. Chem Soc Rev 2017; 46:4329-4346. [DOI: 10.1039/c6cs00912c] [Citation(s) in RCA: 261] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
This review highlights recent advances in radical cascade cyclization of 1,n-enynes and diynes for the construction of carbo- and heterocycles.
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Affiliation(s)
- Jun Xuan
- Department of Chemistry
- Anhui University
- Hefei
- People's Republic of China
| | - Armido Studer
- Institute of Organic Chemistry
- Westfälische Wilhems-University
- 48149 Münster
- Germany
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16
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Methoxycarbonyl migration in 3-methylene-1,4-cyclohexadienes. An extension of the von Auwers rearrangement. Tetrahedron 2016. [DOI: 10.1016/j.tet.2016.03.032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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17
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Yu JT, Pan C. Radical C–H functionalization to construct heterocyclic compounds. Chem Commun (Camb) 2016; 52:2220-36. [DOI: 10.1039/c5cc08872k] [Citation(s) in RCA: 106] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Radical C–H functionalization is a promising and dramatic approach to synthesize heterocyclic compounds with high efficiency and environmental sustainability.
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Affiliation(s)
- Jin-Tao Yu
- School of Petrochemical Engineering
- Advanced Catalysis and Green Manufacturing Collaborative Innovation Center
- Changzhou University
- Changzhou 213164
- P. R. China
| | - Changduo Pan
- School of Chemistry & Environmental Engineering
- Jiangsu University of Technology
- Changzhou 213001
- P. R. China
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18
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20
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Keess S, Simonneau A, Oestreich M. Direct and Transfer Hydrosilylation Reactions Catalyzed by Fully or Partially Fluorinated Triarylboranes: A Systematic Study. Organometallics 2015. [DOI: 10.1021/om501284a] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Sebastian Keess
- Institut
für Chemie, Technische Universität Berlin, Strasse des 17.
Juni 115, 10623 Berlin, Germany
| | - Antoine Simonneau
- Institut
für Chemie, Technische Universität Berlin, Strasse des 17.
Juni 115, 10623 Berlin, Germany
| | - Martin Oestreich
- Institut
für Chemie, Technische Universität Berlin, Strasse des 17.
Juni 115, 10623 Berlin, Germany
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21
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Leifert D, Studer A. 9-Silafluorenes via base-promoted homolytic aromatic substitution (BHAS)--the electron as a catalyst. Org Lett 2014; 17:386-9. [PMID: 25536028 DOI: 10.1021/ol503574k] [Citation(s) in RCA: 106] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Transition-metal-free intramolecular radical silylation of 2-diphenylsilylbiaryls via base-promoted homolytic aromatic substitution (BHAS) to give 9-silafluorenes is reported. 2-Diphenylsilylbiaryls are readily prepared, and cross dehydrogenative silylation occurs with tert-butylhydroperoxide (TBHP) as a cheap stoichiometric oxidant in the presence of a small amount of tetrabutylammonium iodide (TBAI) as an initiator. These cyclizations are catalyzed by the electron.
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Affiliation(s)
- Dirk Leifert
- Institute of Organic Chemistry, Westfälische Wilhelms-Universität , Corrensstraße 40, 48149 Münster, Germany
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22
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Rousseau G, Lebeuf R, Schenk K, Castet F, Robert F, Landais Y. Base-catalyzed intramolecular hydroamination of cyclohexa-2,5-dienes: insights into the mechanism through DFT calculations and application to the total synthesis of epi-elwesine. Chemistry 2014; 20:14771-82. [PMID: 25223607 DOI: 10.1002/chem.201403662] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Revised: 07/10/2014] [Indexed: 11/08/2022]
Abstract
The base-catalyzed intramolecular hydroamination of 1-ethylaminocyclohexa-2,5-dienes is described. The transformation proceeds through isomerization of the cyclohexa-1,4-dienyl fragment into the corresponding conjugated 1,3-diene prior to the hydroamination step. Attaching a chiral glycinol ether auxiliary on the amino group allows the protonation to occur with complete diastereocontrol. The resulting lithium amide then adds onto the 1,3-dienyl moiety, affording the desired fused pyrrolidine ring along with the corresponding lithium allylic anion. Protonation of the latter then proceeds with high regiocontrol to favor the resulting allylic amines. In contrast, when the reaction was performed on primary amines, fused pyrrolidines bearing a homoallylic amino group were obtained. The stereochemical course of the process and determination of the reaction pathways were established based on calculations performed at the DFT level. Finally, application of the methodology to the enantioselective synthesis of (+)-epi-elwesine, a crinane alkaloid, is described.
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Affiliation(s)
- Géraldine Rousseau
- ISM, UMR 5255, University of Bordeaux and CNRS, 351, Cours de la liberation, 33400 Talence Cedex (France)
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23
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A two-step, single pot procedure for the synthesis of substituted dihydropyrazolo-pyrimidines. Tetrahedron Lett 2014. [DOI: 10.1016/j.tetlet.2013.12.057] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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24
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Li G, Wu L, Lv G, Liu H, Fu Q, Zhang X, Tang Z. Alkyl transfer from C–C cleavage: replacing the nitro group of nitro-olefins. Chem Commun (Camb) 2014; 50:6246-8. [DOI: 10.1039/c4cc01119h] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Hydrogenation is only the beginning: alkyl groups are mildly transferred from alkyl substituted Hantzsch esters to replace the nitro groups of nitro olefins to providetrans-olefins in moderate to excellent yields.
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Affiliation(s)
- Guangxun Li
- Natural Products Research Center
- Chengdu Institution of Biology
- Chinese Academy of Science
- Chengdu, China
| | - Lei Wu
- Natural Products Research Center
- Chengdu Institution of Biology
- Chinese Academy of Science
- Chengdu, China
| | - Gang Lv
- Natural Products Research Center
- Chengdu Institution of Biology
- Chinese Academy of Science
- Chengdu, China
| | - Hongxin Liu
- Natural Products Research Center
- Chengdu Institution of Biology
- Chinese Academy of Science
- Chengdu, China
| | - Qingquan Fu
- Natural Products Research Center
- Chengdu Institution of Biology
- Chinese Academy of Science
- Chengdu, China
| | - Xiaomei Zhang
- Chengdu Institute of Organic Chemistry
- Chinese Academy of Sciences
- Chengdu, China
| | - Zhuo Tang
- Natural Products Research Center
- Chengdu Institution of Biology
- Chinese Academy of Science
- Chengdu, China
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25
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Abstract
This review article focuses on state-of-the-art borohydride based radical reactions, also covering earlier work, kinetics and some DFT calculations with respect to the hydrogen transfer mechanism.
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Affiliation(s)
- Takuji Kawamoto
- Department of Chemistry
- Graduate School of Science
- Osaka Prefecture University
- Sakai, Japan
| | - Ilhyong Ryu
- Department of Chemistry
- Graduate School of Science
- Osaka Prefecture University
- Sakai, Japan
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26
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Huang Z, Jin L, Feng Y, Peng P, Yi H, Lei A. Iron-catalyzed oxidative radical cross-coupling/cyclization between phenols and olefins. Angew Chem Int Ed Engl 2013; 52:7151-5. [PMID: 23733624 DOI: 10.1002/anie.201210023] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2012] [Revised: 04/16/2013] [Indexed: 11/05/2022]
Affiliation(s)
- Zhiliang Huang
- The College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, 430072, Hubei, P.R. China
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Huang Z, Jin L, Feng Y, Peng P, Yi H, Lei A. Iron-Catalyzed Oxidative Radical Cross-Coupling/Cyclization between Phenols and Olefins. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201210023] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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28
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Mitsudo K, Nakagawa Y, Mizukawa JI, Tanaka H, Akaba R, Okada T, Suga S. Electro-reductive cyclization of aryl halides promoted by fluorene derivatives. Electrochim Acta 2012. [DOI: 10.1016/j.electacta.2012.03.130] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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29
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Hierold J, Lupton DW. Synthesis of Spirocyclic γ-Lactones by Cascade Beckwith–Dowd Ring Expansion/Cyclization. Org Lett 2012; 14:3412-5. [DOI: 10.1021/ol301386k] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Judith Hierold
- School of Chemistry, Monash University, Clayton 3800, Victoria, Australia
| | - David W. Lupton
- School of Chemistry, Monash University, Clayton 3800, Victoria, Australia
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Rouquet G, Robert F, Méreau R, Castet F, Renaud P, Landais Y. Silylboranes as new sources of silyl radicals for chain-transfer reactions. Chemistry 2012; 18:940-50. [PMID: 22180016 DOI: 10.1002/chem.201102318] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Indexed: 11/05/2022]
Abstract
Various silylboranes, which were outfitted with a catecholborane moiety at one end and a (Me(3)Si)(3)Si moiety at the other end of a carbon chain, were prepared through the hydroboration of the corresponding unsaturated silanes. The C-centered radical species generated from these silylboranes efficiently cyclized to provide, through a 5-exo intramolecular homolytic substitution at the silicon center, the corresponding silacycle and a Me(3)Si radical that was subsequently trapped by sulfonyl acceptors. These cyclizations proceeded at unprecedented rates, due, in part, to a strong gem-dialkyl effect that was attributable to the presence of bulky substituents on a quaternary center located on the chain. In parallel, we designed arylsilylboranes that produced silyl radicals through a 1,5-hydrogen transfer. Such silyl radicals may be valuable radical chain carriers, for instance, in oximation reactions of alkyl halides. Finally, computational studies allowed calculation of activation barriers of the homolytic substitution step and additionally illustrated that the overall reaction mechanism involved a transition state in which the attacking carbon center, the central silicon atom, and the Me(3)Si leaving group were collinear.
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Affiliation(s)
- Guy Rouquet
- Université de Bordeaux, Institut des Sciences Moléculaires, UMR-CNRS 5255, 351, Cours de la libération 33405 Talence Cedex, France
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31
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Zimmerman JR, Manpadi M, Spatney R, Baker A. Diastereoselective Tin-Free Tandem Radical Additions to 3-Formylchromones. J Org Chem 2011; 76:8076-81. [DOI: 10.1021/jo201350w] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jake R. Zimmerman
- Department of Chemistry and Biochemistry, Ohio Northern University, Ada, Ohio 45810, United States
| | - Madhuri Manpadi
- Department of Chemistry and Biochemistry, Ohio Northern University, Ada, Ohio 45810, United States
| | - Russell Spatney
- Department of Chemistry and Biochemistry, Ohio Northern University, Ada, Ohio 45810, United States
| | - Aaron Baker
- Department of Chemistry and Biochemistry, Ohio Northern University, Ada, Ohio 45810, United States
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32
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Studer A, Curran DP. Organocatalysis and C-H activation meet radical- and electron-transfer reactions. Angew Chem Int Ed Engl 2011; 50:5018-22. [PMID: 21523871 DOI: 10.1002/anie.201101597] [Citation(s) in RCA: 412] [Impact Index Per Article: 31.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Indexed: 11/09/2022]
Affiliation(s)
- Armido Studer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany.
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33
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Organokatalyse und C-H-Aktivierung treffen auf Radikal- und Elektronentransferreaktionen. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201101597] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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34
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Chou C, Guin J, Mück‐Lichtenfeld C, Grimme S, Studer A. Radical‐Transfer Hydroamination of Olefins with N‐Aminated Dihydropyridines. Chem Asian J 2011; 6:1197-209. [DOI: 10.1002/asia.201000881] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2011] [Indexed: 11/09/2022]
Affiliation(s)
- Chih‐Ming Chou
- Organisch‐Chemisches Institut, Westfälische Wilhelms‐Universität Münster, Corrensstrasse 40, 48149 Münster (Germany), Fax: (+49) 251‐8336523
| | - Joyram Guin
- Organisch‐Chemisches Institut, Westfälische Wilhelms‐Universität Münster, Corrensstrasse 40, 48149 Münster (Germany), Fax: (+49) 251‐8336523
| | - Christian Mück‐Lichtenfeld
- Organisch‐Chemisches Institut, Westfälische Wilhelms‐Universität Münster, Corrensstrasse 40, 48149 Münster (Germany), Fax: (+49) 251‐8336523
| | - Stefan Grimme
- Organisch‐Chemisches Institut, Westfälische Wilhelms‐Universität Münster, Corrensstrasse 40, 48149 Münster (Germany), Fax: (+49) 251‐8336523
| | - Armido Studer
- Organisch‐Chemisches Institut, Westfälische Wilhelms‐Universität Münster, Corrensstrasse 40, 48149 Münster (Germany), Fax: (+49) 251‐8336523
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35
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McBurney RT, Slawin AMZ, Smart LA, Yu Y, Walton JC. UV promoted phenanthridine syntheses from oxime carbonate derived iminyl radicals. Chem Commun (Camb) 2011; 47:7974-6. [DOI: 10.1039/c1cc12720a] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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36
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Sibi MP, Yang YH, Lee S. Tin-free enantioselective radical reactions using silanes. Org Lett 2010; 10:5349-52. [PMID: 18986157 DOI: 10.1021/ol802154d] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Readily available hexyl silane is an excellent choice as a H-atom donor and a chain carrier in Lewis acid mediated enantioselective radical reactions. Conjugate radical additions to alpha,beta-unsaturated imides at room temperature proceed in good yields and excellent enantioselectivities.
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Affiliation(s)
- Mukund P Sibi
- Department of Chemistry, North Dakota State University, Fargo, North Dakota 58105, USA.
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37
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Larraufie MH, Courillon C, Ollivier C, Lacôte E, Malacria M, Fensterbank L. Radical migration of substituents of aryl groups on quinazolinones derived from N-acyl cyanamides. J Am Chem Soc 2010; 132:4381-7. [PMID: 20205425 DOI: 10.1021/ja910653k] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A newly designed radical cascade involving N-acyl cyanamides is reported. It builds on aromatic homolytic substitutions as intermediate events and leads to complex heteroaromatic structures via an unprecedented radical migration of a substituent on aryl groups of quinazolinones (hydrogen or alkyl). Mechanistic considerations are detailed, which allowed us to devise fine control over the domino processes. The latter could be predictably stopped at several stages, depending on the reaction conditions. Finally, a surgical introduction of a trifluoromethyl substituent on a quinazolinone was achieved via the reported migration.
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Affiliation(s)
- Marie-Hélène Larraufie
- UPMC Univ Paris 06, Institut Parisien de Chimie Moleculaire (UMR CNRS 7201), C. 229, 4 Place Jussieu, 75005 Paris, France
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38
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Harrowven DC, Curran DP, Kostiuk SL, Wallis-Guy IL, Whiting S, Stenning KJ, Tang B, Packard E, Nanson L. Potassium carbonate–silica: a highly effective stationary phase for the chromatographic removal of organotin impurities. Chem Commun (Camb) 2010; 46:6335-7. [DOI: 10.1039/c0cc01328e] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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39
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Bencivenni G, Lanza T, Minozzi M, Nanni D, Spagnolo P, Zanardi G. Radical allylations by reaction of azides with allylindium dichloride. Org Biomol Chem 2010; 8:3444-50. [DOI: 10.1039/c001848a] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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40
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Maji MS, Fröhlich R, Studer A. Desymmetrization of Metallated Cyclohexadienes with Chiral N-tert-Butanesulfinyl Imines. Org Lett 2008; 10:1847-50. [DOI: 10.1021/ol800478q] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Modhu Sudan Maji
- NRW Graduate School of Chemistry and Fachbereich Chemie, Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
| | - Roland Fröhlich
- NRW Graduate School of Chemistry and Fachbereich Chemie, Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
| | - Armido Studer
- NRW Graduate School of Chemistry and Fachbereich Chemie, Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
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42
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Beaume A, Courillon C, Derat E, Malacria M. Unprecedented Aromatic Homolytic Substitutions and Cyclization of AmideIminyl Radicals: Experimental and Theoretical Study. Chemistry 2008; 14:1238-52. [DOI: 10.1002/chem.200700884] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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43
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Chatgilialoglu C, Timokhin VI. Silyl Radicals in Chemical Synthesis. ADVANCES IN ORGANOMETALLIC CHEMISTRY 2008. [DOI: 10.1016/s0065-3055(08)00002-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
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44
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Guin J, Mück-Lichtenfeld C, Grimme S, Studer A. Radical Transfer Hydroamination with Aminated Cyclohexadienes Using Polarity Reversal Catalysis: Scope and Limitations. J Am Chem Soc 2007; 129:4498-503. [PMID: 17371026 DOI: 10.1021/ja0692581] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The synthesis of various new 1-aminated-2,5-cyclohexadienes is described. These reagents can be used in radical transfer hydroaminations of unactivated and electron-rich double bonds. With thiols as polarity reversal catalysts good yields are obtained. The radical hydroamination occurs with good to excellent anti-Markovnikov selectivity. Many functional groups such as alcohols, silyl ethers, phosphonates, arylbromides, imides, amides, and also acidic protons are tolerated under the reaction conditions. DFT calculations provide insights into the aromatization of silyl, alkyl, and aminyl substituted cyclohexadienyl radicals to generate the corresponding C-, Si-, and N-centered radicals.
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Affiliation(s)
- Joyram Guin
- Fachbereich Chemie, Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster
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45
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Marshall LJ, Roydhouse MD, Slawin AMZ, Walton JC. Effect of Chain Length on Radical to Carbanion Cyclo-Coupling of Bromoaryl Alkyl-Linked Oxazolines: 1,3-Areneotropic Migration of Oxazolines. J Org Chem 2007; 72:898-911. [PMID: 17253809 DOI: 10.1021/jo0620720] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
2-Halophenylalkyl-2-oxazolines with alkyl chain spacers of two to six C atoms (n = 0-4) were prepared and their SRN1-type reactions with several base systems examined. The best conditions to promote cyclo-coupling to the corresponding benzocycloalkane derivatives involved use of LDA in THF. The precursors with 3-C-atom and 4-C-atom spacers gave good yields of 2-(1'-phenylindan-1'-yl)-2-oxazolines and 2-(1-phenyl-1,2,3,4-tetrahydronaphthalen-1-yl)-2-oxazoline, respectively. The major products from the precursor with a 5-C-atom spacer were derivatives of benzocycloheptane in which the oxazoline group had undergone a novel areneotropic migration from the end of the spacer to the benzo ring. The product from reaction of the corresponding 2-C-atom precursor was a 9-oxazolinophenanthrene derivative. EPR spectroscopy showed the intermediates of the LDA-promoted reactions to be radical anions of the product benzocycloalkanes. This supported an SRN1-type chain mechanism involving initial production of aryl radicals connected to azaenolate ions via the spacer groups. Intramolecular radical to carbanion coupling then generated ring-closed benzocycloalkane radical anions that transferred an electron to more precursor. Diastereoselective radical to carbanion cyclo-coupling reactions were carried out with 2-bromophenylpropyl precursors containing chiral 2-oxazolines. The diastereoselectivity achievable was modest, but the product diastereoisomeric Indane derivatives were easily separable by chromatography.
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Affiliation(s)
- Laura J Marshall
- University of Saint Andrews, EastChem, School of Chemistry, Saint Andrews, Fife, KY16 9ST, United Kingdom
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46
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Anions from dihydro substituted ethyl benzoates and quinoline. New hydrogen donors for tin-free radical chemistry. Tetrahedron Lett 2006. [DOI: 10.1016/j.tetlet.2006.02.139] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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47
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Hein JE, Zimmerman J, Sibi MP, Hultin PG. Stereoselective conjugate radical additions: application of a fluorous oxazolidinone chiral auxiliary for efficient tin removal. Org Lett 2006; 7:2755-8. [PMID: 15957939 PMCID: PMC1524859 DOI: 10.1021/ol050956k] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
[reaction: see text] A series of asymmetric free-radical-mediated intermolecular conjugate additions using a fluorous oxazolidinone chiral auxiliary has been completed. The fluorous auxiliary facilitated product isolation using fluorous solid phase extractions (FSPE), effectively removing excess organic and organometallic reagents. Parallel reactions carried out with a similar but nonfluorous norephedrine-derived oxazolidinone demonstrated the superior stereoselectivity and purification obtainable with the fluorous chiral auxiliary.
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Affiliation(s)
- Jason E Hein
- Department of Chemistry, University of Manitoba, Winnipeg, MB, R3T 2N2 Canada
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48
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Save M, Guillaneuf Y, Gilbert RG. Controlled Radical Polymerization in Aqueous Dispersed Media. Aust J Chem 2006. [DOI: 10.1071/ch06308] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Controlled radical polymerization (CRP), sometimes also termed ‘living’ radical polymerization, offers the potential to create a wide range of polymer architectures, and its implementation in aqueous dispersed media (e.g. emulsion polymerization, used on a vast scale industrially) opens the way to large-scale manufacture of products based on this technique. Until recently, implementing CRP in aqueous dispersed media was plagued with problems such as loss of ‘living’ character and loss of colloidal stability. This review examines the basic mechanistic processes in free-radical polymerization in aqueous dispersed media (e.g. emulsion polymerization), and then examines, through this mechanistic understanding, the new techniques that have been developed over the last few years to implement CRP successfully in emulsion polymerizations and related processes. The strategies leading to these successes can thus be understood in terms of the various mechanisms which dominate CRP systems in dispersed media; these mechanisms are sometimes quite different from those in conventional free-radical polymerization in these media.
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49
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Majumdar KC, Basu PK, Mukhopadhyay PP. Formation of five- and six-membered heterocyclic rings under radical cyclisation conditions. Tetrahedron 2005. [DOI: 10.1016/j.tet.2005.07.079] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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50
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Walton JC, Studer A. Evolution of functional cyclohexadiene-based synthetic reagents: the importance of becoming aromatic. Acc Chem Res 2005; 38:794-802. [PMID: 16231875 DOI: 10.1021/ar050089j] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Suites of new precursors designed around a cyclohexadiene core and intended to mediate "clean" radical chain syntheses have been prepared and tested. 1-Functionalized cyclohexa-2,5-dienes were found to readily donate H-atoms, and the resulting cyclohexadienyl radicals rapidly extruded their functional group as a free radical, because this beta-scission restored aromaticity to the ring. This concept was employed to generate designer radicals from esters of the corresponding alcohols with 1-methyl- or 1-phenylcyclohexa-2,5-diene-1-carboxylic acids. In a similar way, pre-adapted carbamoyl radicals were obtained from cyclohexadienyl-amides and proved advantageous for syntheses of alpha- and beta-lactams. Oxime ether substituted carbamoyl radicals cyclized successfully in convenient syntheses of dihydroindolin-2-ones with N-functionality at the 3-position. Similarly, silicon-centered radicals were obtained from 1-silylated cyclohexadienes, and these reagents proved to be very efficient, environmentally benign organotin hydride substitutes. Radical reactions including reductions, cyclizations, intermolecular additions, and hydrosilylations were carried out in high yields with this reagent. Other heteroatom-centered radicals, especially N-centered radicals, were obtained from appropriate cyclohexadienes enabling chain hydroaminations to be conducted. Several of the cyclohexadiene precursors proved to be useful for electron paramagnetic resonance (EPR) spectroscopic purposes, and this enabled rate constants for fragmentations of the cyclohexadienyl radicals to be obtained. Kinetic data for H-atom abstraction from cyclohexadienes, the second propagation step of the chain processes, was derived from customized radical clocks and from EPR measurements. In this way, conceptual tools were developed for improving future synthetic methodology based around these reagents.
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Affiliation(s)
- John C Walton
- School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, U.K
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