标题：Activation of C-H Bonds through Oxidant-Free Photoredox Catalysis: Cross-Coupling Hydrogen-Evolution Transformation of Isochromans and beta-Keto Esters
作者：Xiang, Ming; Meng, Qing-Yuan; Li, Jia-Xin; Zheng, Yi-Wen; Ye, Chen; Li, Zhi-Jun; Chen, Bin; Tung, Chen-Ho; Wu, Li-Zhu
作者机构：[Xiang, Ming; Meng, Qing-Yuan; Li, Jia-Xin; Ye, Chen; Li, Zhi-Jun; Chen, Bin; Tung, Chen-Ho; Wu, Li-Zhu] Chinese Acad Sci, Tech Inst Phys & Chem, Key 更多
通讯作者地址：[Wu, LZ]Chinese Acad Sci, Tech Inst Phys & Chem, Key Lab Photochem Convers & Optoelect Mat, Beijing 100190, Peoples R China.
来源：CHEMISTRY-A EUROPEAN JOURNAL
关键词：C-H activation; isochromans; oxonium; photoredox catalysis
摘要：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(dmgBF(2))(2)center dot 2MeCN, dmg=dimethylglyoxime), the nucleophilic addition of beta-keto esters to oxonium species, which is rarely observed in photocatalysis, leads to the corresponding coupling products and H-2 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.