title: Activation of CH Bonds through Oxidant-Free Photoredox Catalysis: Cross-Coupling Hydrogen-Evolution Transformation of Isochromans and β-Keto Esters.
abstract: The direct and controlled activation of a C(sp(3) )H bond adjacent to an O atom is of particular synthetic value for the conventional derivatization of ethers or alcohols. In general, stoichiometric amounts of an oxidant are required to remove an electron and a hydrogen atom of the ether for subsequent transformations. Herein, we demonstrate that the activation of a CH bond next to an O atom could be achieved under oxidant-free conditions through photoredox-neutral catalysis. By using a commercial dyad photosensitizer (Acr(+) -Mes ClO4 (-) , 9-mesityl-10-methylacridinium perchlorate) and an easily available cobaloxime complex (Co(dmgBF2 )2 ⋅2 MeCN, dmg=dimethylglyoxime), the nucleophilic addition of β-keto esters to oxonium species, which is rarely observed in photocatalysis, leads to the corresponding coupling products and H2 in moderate to good yields under visible-light irradiation. Mechanistic studies suggest that both isochroman and the cobaloxime complex quench the electron-transfer state of this dyad photosensitizer and that benzylic CH bond cleavage is probably the rate-determining step of this cross-coupling hydrogen-evolution transformation.
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
authors.forename: Ming
authors.initials: M
authors.lastname: Xiang
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
authors.forename: Qing-Yuan
authors.initials: QY
authors.lastname: Meng
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
authors.forename: Jia-Xin
authors.initials: JX
authors.lastname: Li
authors.affiliation: School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100 (P. R. China).
authors.forename: Yi-Wen
authors.initials: YW
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
authors.forename: Chen
authors.initials: C
authors.lastname: Ye
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
authors.forename: Zhi-Jun
authors.initials: ZJ
authors.lastname: Li
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
authors.forename: Chen-Ho
authors.initials: CH
authors.lastname: Tung
authors.affiliation: Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190 (P. R. China). lzwu@mail.ipc.ac.cn.
authors.forename: Li-Zhu
authors.initials: LZ
authors.lastname: Wu
keywords: CH activation; isochromans; oxonium; photoredox catalysis