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Open AccessOpen Access JUSTC Chemistry 17 January 2024

Highly efficient copper-catalyzed benzylic C–H alkoxylation with NFSI

  • Hefei National Research Center for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, China

Cite this:
https://doi.org/10.52396/JUSTC-2023-0080
More Information
  • Author Bio:

    Cheng Zhang received his master’s degree from the University of Science and Technology of China, under the supervision of Prof. Liu-Zhu Gong. His research mainly focuses on green synthesis and catalysis

    Pu-Sheng Wang received his Ph.D. degree in Chemistry from the University of Science and Technology of China. He is currently an Associate Professor at the University of Science and Technology of China. His research interests include asymmetric catalysis and radical chemistry

  • Corresponding author: E-mail: pusher@ustc.edu.cn
  • Received Date: 03 May 2023
  • Accepted Date: 19 June 2023
    • Available Online: 17 January 2024
    Abstract

  • Abstract

    A sacrificial reductant-free copper-catalyzed benzylic C–H alkoxylation with N-Fluorobenzenesulfonimide (NFSI) was reported. Mechanistic studies suggested a novel pathway for the generation of active CuI species from Cu(OAc)2, NFSI and MeOH. A proper loading amount of copper catalyst was found to balance the reaction rates of benzylic C–H alkoxylation and overoxidation of benzyl ether to exhibit the best performance.

    Graphical abstract

    A copper-catalyzed benzylic C–H alkoxylation with NFSI without using an external sacrificial reductant.

    Abstract

    A sacrificial reductant-free copper-catalyzed benzylic C–H alkoxylation with N-Fluorobenzenesulfonimide (NFSI) was reported. Mechanistic studies suggested a novel pathway for the generation of active CuI species from Cu(OAc)2, NFSI and MeOH. A proper loading amount of copper catalyst was found to balance the reaction rates of benzylic C–H alkoxylation and overoxidation of benzyl ether to exhibit the best performance.

    • Public Summary

    • A sacrificial reductant-free copper-catalyzedbenzylic C–H alkoxylation with NFSI is disclosed.
    • Mechanistic studies suggest a new pathway togenerate CuI from CuII.
    • This reaction provides an attractive approach forthe synthesis of benzyl ethers.

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    • References(20)
  • [1]
    Brown A, Brown L, Brown T B, et al. Triazole oxytocin antagonists: identification of aryl ether replacements for a biaryl substituent. Bioorg. Med. Chem. Lett., 2008, 18 (19): 5242–5244. doi: 10.1016/j.bmcl.2008.08.066
    [2]
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    [3]
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    Oliva M, Coppola G A, van der Eycken E V, et al. Photochemical and electrochemical strategies towards benzylic C−H functionalization: a recent update. Adv. Synth. Catal., 2021, 363 (7): 1810–1834. doi: 10.1002/adsc.202001581
    [8]
    Yue H, Zhu C, Huang L, et al. Advances in allylic and benzylic C–H bond functionalization enabled by metallaphotoredox catalysis. Chem. Commun., 2021, 58 (2): 171–184. doi: 10.1039/D1CC06285A
    [9]
    Güven Ö Ö, Erdoğan T, Göker H, et al. Synthesis and antimicrobial activity of some novel phenyl and benzimidazole substituted benzyl ethers. Bioorg. Med. Chem. Lett., 2007, 17 (8): 2233–2236. doi: 10.1016/j.bmcl.2007.01.061
    [10]
    Lee B J, DeGlopper K S, Yoon T P. Site-selective alkoxylation of benzylic C–H bonds by photoredox catalysis. Angew. Chem. Int. Ed., 2020, 59 (1): 197–202. doi: 10.1002/anie.201910602
    [11]
    Zhang Y, Sahoo P K, Ren P, et al. Transition metal-free approach for late-stage benzylic C(sp3)–H etherifications and esterifications. Chem. Commun., 2022, 58 (81): 11454–11457. doi: 10.1039/D2CC02661A
    [12]
    Bo C, Chen F, Bu Q, et al. Visible-light-driven organocatalytic alkoxylation of benzylic C–H bonds. J. Org. Chem., 2023, 88 (6): 3532–3538. doi: 10.1021/acs.joc.2c02743
    [13]
    Wang H M, Liang K L, Xiong W P, et al. Electrochemical oxidation-induced etherification via C(sp3)–H/O–H cross-coupling. Sci. Adv., 2020, 6 (20): eaaz0590. doi: 10.1126/sciadv.aaz0590
    [14]
    Dong M, Jia Y Q, Zhou W, et al. A photoredox/nickel dual-catalytic strategy for benzylic C–H alkoxylation. Org. Chem. Front., 2021, 8 (24): 6881–6887. doi: 10.1039/D1QO01421H
    [15]
    Hu H Y, Chen S J, Mandal M, et al. Copper-catalysed benzylic C–H coupling with alcohols via radical relay enabled by redox buffering. Nat. Catal., 2020, 3 (4): 358–367. doi: 10.1038/s41929-020-0425-1
    [16]
    Wang F, Chen P H, Liu G S. Copper-catalyzed radical relay for asymmetric radical transformations. Acc. Chem. Res., 2018, 51 (9): 2036–2046. doi: 10.1021/acs.accounts.8b00265
    [17]
    Dai Z Y, Zhang S Q, Hong X, et al. A practical FeCl3/HCl photocatalyst for versatile aliphatic C–H functionalization. Chem. Catal., 2022, 2 (5): 1211–1222. doi: 10.1016/j.checat.2022.03.020
    [18]
    Jiajun D, Maza J R, Xu Y, et al. A stress tensor and QTAIM perspective on the substituent effects of biphenyl subjected to torsion. J. Comput. Chem., 2016, 37 (28): 2508–2517. doi: 10.1002/jcc.24476
    [19]
    Lu Q Q, Zhang J, Peng P, et al. Operando X-ray absorption and EPR evidence for a single electron redox process in copper catalysis. Chem. Sci., 2015, 6 (8): 4851–4854. doi: 10.1039/C5SC00807G
    [20]
    Golden D L, Zhang C F, Chen S J, et al. Benzylic C–H esterification with limiting C–H substrate enabled by photochemical redox buffering of the Cu catalyst. J. Am. Chem. Soc., 2023, 145 (17): 9434–9440. doi: 10.1021/jacs.3c01662
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    Figure  1.  Strategies toward benzylic C−H alkoxylation.

    Figure  2.  Scope of substrates. Reaction conditions: alkylarene 1 (0.10 mmol), alcohol 2 (0.50 mmol), NFSI (0.13 mmol), Cu(OAc)2 (0.01 mol%), MeCN (0.5 mL), 80 °C, 12 h, under argon atmosphere. Isolated yield.

    Figure  3.  Kinetic studies.

    Figure  4.  Mechanistic studies.

    Figure  5.  Proposed catalytic cycle.

    [1]
    Brown A, Brown L, Brown T B, et al. Triazole oxytocin antagonists: identification of aryl ether replacements for a biaryl substituent. Bioorg. Med. Chem. Lett., 2008, 18 (19): 5242–5244. doi: 10.1016/j.bmcl.2008.08.066
    [2]
    Hagmann W K. The many roles for fluorine in medicinal chemistry. J. Med. Chem., 2008, 51 (15): 4359–4369. doi: 10.1021/jm800219f
    [3]
    Broccatelli F, Carosati E, Neri A, et al. A novel approach for predicting P-glycoprotein (ABCB1) inhibition using molecular interaction fields. J. Med. Chem., 2011, 54 (6): 1740–1751. doi: 10.1021/jm101421d
    [4]
    Rani N, Sharma A, Gupta G K, et al. Imidazoles as potential antifungal agents: a review. Mini-Rev. Med. Chem., 2013, 13 (11): 1626–1655. doi: 10.2174/13895575113139990069
    [5]
    Fuhrmann E, Talbiersky J. Synthesis of alkyl aryl ethers by catalytic Williamson ether synthesis with weak alkylation agents. Org. Process Res. Dev., 2005, 9 (2): 206–211. doi: 10.1021/op050001h
    [6]
    Huang H, Nelson C G, Taber D F. Potassium hydride in paraffin: a useful base for Williamson ether synthesis. Tetrahedron Lett., 2010, 51 (27): 3545–3546. doi: 10.1016/j.tetlet.2010.04.129
    [7]
    Oliva M, Coppola G A, van der Eycken E V, et al. Photochemical and electrochemical strategies towards benzylic C−H functionalization: a recent update. Adv. Synth. Catal., 2021, 363 (7): 1810–1834. doi: 10.1002/adsc.202001581
    [8]
    Yue H, Zhu C, Huang L, et al. Advances in allylic and benzylic C–H bond functionalization enabled by metallaphotoredox catalysis. Chem. Commun., 2021, 58 (2): 171–184. doi: 10.1039/D1CC06285A
    [9]
    Güven Ö Ö, Erdoğan T, Göker H, et al. Synthesis and antimicrobial activity of some novel phenyl and benzimidazole substituted benzyl ethers. Bioorg. Med. Chem. Lett., 2007, 17 (8): 2233–2236. doi: 10.1016/j.bmcl.2007.01.061
    [10]
    Lee B J, DeGlopper K S, Yoon T P. Site-selective alkoxylation of benzylic C–H bonds by photoredox catalysis. Angew. Chem. Int. Ed., 2020, 59 (1): 197–202. doi: 10.1002/anie.201910602
    [11]
    Zhang Y, Sahoo P K, Ren P, et al. Transition metal-free approach for late-stage benzylic C(sp3)–H etherifications and esterifications. Chem. Commun., 2022, 58 (81): 11454–11457. doi: 10.1039/D2CC02661A
    [12]
    Bo C, Chen F, Bu Q, et al. Visible-light-driven organocatalytic alkoxylation of benzylic C–H bonds. J. Org. Chem., 2023, 88 (6): 3532–3538. doi: 10.1021/acs.joc.2c02743
    [13]
    Wang H M, Liang K L, Xiong W P, et al. Electrochemical oxidation-induced etherification via C(sp3)–H/O–H cross-coupling. Sci. Adv., 2020, 6 (20): eaaz0590. doi: 10.1126/sciadv.aaz0590
    [14]
    Dong M, Jia Y Q, Zhou W, et al. A photoredox/nickel dual-catalytic strategy for benzylic C–H alkoxylation. Org. Chem. Front., 2021, 8 (24): 6881–6887. doi: 10.1039/D1QO01421H
    [15]
    Hu H Y, Chen S J, Mandal M, et al. Copper-catalysed benzylic C–H coupling with alcohols via radical relay enabled by redox buffering. Nat. Catal., 2020, 3 (4): 358–367. doi: 10.1038/s41929-020-0425-1
    [16]
    Wang F, Chen P H, Liu G S. Copper-catalyzed radical relay for asymmetric radical transformations. Acc. Chem. Res., 2018, 51 (9): 2036–2046. doi: 10.1021/acs.accounts.8b00265
    [17]
    Dai Z Y, Zhang S Q, Hong X, et al. A practical FeCl3/HCl photocatalyst for versatile aliphatic C–H functionalization. Chem. Catal., 2022, 2 (5): 1211–1222. doi: 10.1016/j.checat.2022.03.020
    [18]
    Jiajun D, Maza J R, Xu Y, et al. A stress tensor and QTAIM perspective on the substituent effects of biphenyl subjected to torsion. J. Comput. Chem., 2016, 37 (28): 2508–2517. doi: 10.1002/jcc.24476
    [19]
    Lu Q Q, Zhang J, Peng P, et al. Operando X-ray absorption and EPR evidence for a single electron redox process in copper catalysis. Chem. Sci., 2015, 6 (8): 4851–4854. doi: 10.1039/C5SC00807G
    [20]
    Golden D L, Zhang C F, Chen S J, et al. Benzylic C–H esterification with limiting C–H substrate enabled by photochemical redox buffering of the Cu catalyst. J. Am. Chem. Soc., 2023, 145 (17): 9434–9440. doi: 10.1021/jacs.3c01662
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