Acta Chimica Sinica ›› 2023, Vol. 81 ›› Issue (5): 435-440.DOI: 10.6023/A23030099 Previous Articles     Next Articles

Communication

连续流条件下蒽-铈协同催化的苄位碳氢键选择性氧化反应

徐袁利a, 潘辉*,b(), 杨义*,a(), 左智伟*,b()   

  1. a 四川轻化工大学化学与环境工程学院 晨光高性能氟材料创新中心 四川自贡 643000
    b 中国科学院上海有机化学研究所 金属有机化学国家重点实验室 上海 200032
  • 投稿日期:2023-03-29 发布日期:2023-05-09
  • 作者简介:
    庆祝《化学学报》创刊90周年.
  • 基金资助:
    受国家自然科学基金(22125111); 受国家自然科学基金(21971163); 国家重点研发计划(2021YFA1500100); 基础研究特区计划-中国科学院上海分院; 四川省科技计划项目(2023NSFSC0097); 晨光高性能氟材料创新中心项目(SCFZ2201)

Selectively Aerobic Oxidation of Benzylic C—H Bonds Enabled by Dual Anthracene and Cerium Catalysis under Continuous-Flow Conditions

Xu Yuanlia, Pan Huib(), Yang Yia(), Zuo Zhiweib()   

  1. a Innovation Center for Chenguang High Performance Fluorine Material, School of Chemical & Environmental Engineering, Sichuan University of Science and Engineering, Zigong, Sichuan 643000
    b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032
  • Received:2023-03-29 Published:2023-05-09
  • Contact: *E-mail: hvpj1102@163.com; yangyiyoung@163.com; zuozhw@sioc.ac.cn
  • About author:
    †These authors contributed equally to this work.
  • Supported by:
    National Natural Science Foundation of China(22125111); National Natural Science Foundation of China(21971163); National Key R&D Program of China(2021YFA1500100); Shanghai Pilot Program for Basic Research-Chinese Academy of Sciences, Shanghai Branch; Sichuan Science and Technology Program(2023NSFSC0097); Innovation Center for Chenguang High Performance Fluorine Material Program(SCFZ2201)

The benzyl oxidation reaction serves as a crucial functional group transformation method in the field of organic synthesis. Regrettably, traditional benzyl oxidation reactions frequently necessitate harsh conditions, such as elevated temperatures and potent oxidizing agents. In contrast, this article showcases a highly selective catalytic benzylic oxidation executed within a continuous-flow microreactor. By harnessing the previously established cerium-alcohol complex’s ligand to metal charge transfer (LMCT)-hydrogen atom transfer (HAT) activation mechanism and the anthracene-cerium synergistic catalytic system, a diverse array of aromatic ketones was synthesized from aryl alkanes with remarkable efficiency under ambient and aerobic conditions. The continuous-flow technology, endowed with unique advantages such as heightened illumination efficiency, superior gas-liquid mass transfer, repeatability, and scalability, has emerged as a powerful instrument for scaling-up photocatalytic reactions. In this process, under flow conditions, ethyl acetate solutions comprising Ce(NO3)3•6H2O, tetrabutylammonium bromide (TBABr), 9,10-dibromoanthracene (DBA), trichloroethanol (TCE), and ethylbenzene encountered and mixed with oxygen within the microreactor. Subsequently, a photocatalytic aerobic oxidation reaction occurred under visible light irradiation at room temperature, achieving complete conversion within a mere 5 min, and rapidly generated a series of aromatic ketones with good to excellent yields. Mechanistic studies indicated the paramount importance of the anthracene-derived catalyst DBA in achieving the heightened efficiency. Under visible light irradiation, the excited state DBA was initially oxidatively quenched with oxygen or peroxide species generated in the system, resulting in the formation of the DBA cationic free radical. Subsequently, the DBA cationic free radical underwent a single electron transfer (SET) process with the low-valent cerium (III) complex, consequently expediting the oxidative regeneration of the cerium (IV) catalyst and markedly boosting its catalytic efficacy. Eventually, this highly efficient catalytic system is characterized by its simplicity, mild reaction conditions, elevated selectivity, minimal waste production, and extensive applicability. Furthermore, it is effortlessly scalable and amenable to continuous production.

Key words: benzyl oxidation, anthracene-cerium dual catalysis, visible-light catalysis, continuous-flow photoreaction