Visible Light-Catalyzed Benzylic C-H Bond Chlorination by a Combination of Organic Dye (Acr+-Mes) and N-Chlorosuccinimide
Ming Xiang, Chao Zhou, Xiu-Long Yang, Bin Chen, Chen-Ho Tung and Li-Zhu Wu*
*University of Chinese Academy of Sciences, The Chinese Academy of Sciences, Beijing 100190, P. R. China,
Email: lzwu
mail.ipc.ac.cn
M. Xiang, C. Zhou, X.-L. Yang, B. Chen, C.-H. Tung, L.-Z. Wu, J. Org. Chem., 2020, 85, 9080-9087.
DOI: 10.1021/acs.joc.0c01000
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Abstract
The combination of N-chlorosuccinimide as safe chlorine source with Acr+-Mes as the photocatalyst achieves a benzylic C-H bond chlorination under visible light irradiation. This mild and scalable chlorination method worked effectively for electron-deficient substrates. Furthermore, benzylic chlorides could be converted to benzylic ethers smoothly in one-pot by adding sodium methoxide.
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Details
The article discusses a novel method for benzylic C−H bond chlorination using N-chlorosuccinimide (NCS) as a safe chlorine source and Acr+-Mes as a photocatalyst under visible light irradiation. This method effectively converts benzylic C−H bonds to benzylic chlorides, which can be further transformed into benzylic ethers using sodium methoxide. The process is mild, scalable, and works well with various toluene derivatives, especially electron-deficient substrates. Mechanistic studies indicate that NCS provides a hydrogen abstractor, the N-centered succinimidyl radical, which facilitates the cleavage of the benzylic C−H bond. The method avoids the use of explosive, corrosive, or toxic chlorine sources and produces fewer byproducts compared to traditional methods. The optimized conditions involve using CH2Cl2 as the solvent and blue LED irradiation for 4 hours. The method also demonstrates good yields for a broad scope of alkylbenzenes and can be scaled up without the need for specialized equipment. This new approach offers a practical and environmentally friendly alternative for benzylic chlorination, with potential applications in pharmaceutical synthesis and fine chemical production.
Key Words
benzylic chlorination, NCS, photochemistry
ID: J42-Y2020
