Selective Electrochemical Oxidation of Benzylic C-H to Benzylic Alcohols with the Aid of Imidazolium Radical Mediators

Fangfang Peng; Junfeng Xiang; Huisheng Qin; Bingfeng Chen; Ran Duan; Wenling Zhao; Shiqiang Liu; Tianbin Wu; Wenli Yuan; Qian Li; Jikun Li; Xinchen Kang; Buxing Han

doi:10.1021/jacs.3c09907

Selective Electrochemical Oxidation of Benzylic C-H to Benzylic Alcohols with the Aid of Imidazolium Radical Mediators

J Am Chem Soc. 2023 Nov 8;145(44):23905-23909. doi: 10.1021/jacs.3c09907. Epub 2023 Oct 27.

Authors

Fangfang Peng¹, Junfeng Xiang^{1

2}, Huisheng Qin^{1

2}, Bingfeng Chen¹, Ran Duan³, Wenling Zhao¹, Shiqiang Liu¹, Tianbin Wu¹, Wenli Yuan¹, Qian Li¹, Jikun Li^{3

2}, Xinchen Kang^{1

2}, Buxing Han^{1

2

4}

Affiliations

¹ Beijing National Laboratory for Molecular Sciences, CAS Laboratory of Colloid and Interface and Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Center for Carbon Neutral Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190 China.
² School of Chemistry, University of Chinese Academy of Sciences, Beijing, 100049 China.
³ Beijing National Laboratory for Molecular Sciences, Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190 China.
⁴ Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai, 200062 China.

PMID: 37890007
DOI: 10.1021/jacs.3c09907

Abstract

Selective oxidation of benzylic C-H to benzylic alcohols is a well-known challenge in the chemical community since benzylic C-H is more prone to be overoxidized to benzylic ketones. In this work, we report the highly selective electro-oxidation of benzylic C-H to benzylic alcohols in an undivided cell in ionic liquid-based solution. As an example, the selectivity toward xanthydrol could be as high as 95.7% at complete conversion of xanthene, a typical benzylic C-H compound, on gram-scale in imidazolium bromide/H₂O/DMF. Mechanism investigation reveals that the imidazolium radical generated in situ participants in a proton-coupled electron transfer process and low-barrier hydrogen bonds stabilize the reaction intermediates, together steering the redox equilibrium, favoring benzylic alcohols over benzylic ketones.