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, Wen‐Li Yuan, Qian Li, Jikun Li, Xinchen Kang, Buxing Han
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/H 2 O/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.