Palladium-Catalyzed Highly Selective ortho-Halogenation (I, Br, Cl) of Arylnitriles via sp2 C-H Bond Activation Using Cyano as Directing Group
Bingnan Du, Xiaoqing Jiang and Peipei Sun*
*Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097, China, Email: sunpeipeinjnu.edu.cn
B. Du, X. Jiang, P. Sun, J. Org. Chem., 2013, 78, 2786-2791.
Using cyano as the directing group, a palladium-catalyzed ortho-halogenation (I, Br, Cl) reaction gave good to excellent yields. The method is compatible to arylnitriles with either electron-withdrawing or electron-donating groups. The present method was successfully applied to the synthesis of the precursors of paucifloral F and isopaucifloral F.
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For the halogenation of 4-methoxybenzonitrile, there is a competition between the palladium-catalyzed ortho-halogenation and an electrophilic substitution (to form 3-halo-methoxybenzonitrile) due to the strong electron-donating property of the methoxyl group.
Peipei Sun, April 27, 2014