Activation of CH Bonds through Oxidant‐Free Photoredox Catalysis: Cross‐Coupling Hydrogen‐Evolution Transformation of Isochromans and β‐Keto Esters |
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Authors: | Ming Xiang Dr Qing‐Yuan Meng Jia‐Xin Li Yi‐Wen Zheng Chen Ye Dr Zhi‐Jun Li Dr Bin Chen Prof?Dr Chen‐Ho Tung Prof?Dr Li‐Zhu Wu |
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Institution: | 1. 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);2. School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100 (P. R. China) |
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Abstract: | The direct and controlled activation of a C(sp3)?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. |
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Keywords: | C H activation isochromans oxonium photoredox catalysis |
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