Palladium-Catalyzed Direct Arylation of 5-Chloropyrazoles: A Selective Access to 4-Aryl Pyrazoles

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• 作者：Tao Yan ; Lu Chen ; Christian Bruneau ; Pierre H. Dixneuf ; Henri Doucet
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：September 7, 2012
• 年：2012
• 卷：77
• 期：17
• 页码：7659-7664
• 全文大小：297K
• 年卷期：v.77,no.17(September 7, 2012)
• ISSN：1520-6904

文摘

The use of a temporary protection by a chloro group at C5 of pyrazoles allows the synthesis of the 4-arylated pyrazoles, which were previously inaccessible by palladium-catalyzed direct arylation, with complete regioselectivity and in high yields using in most cases as little as 0.5鈥?.1 mol % Pd(OAc)₂ as the catalyst with electron-deficient aryl bromides. Moreover, from 5-chloro-1,3-dimethylpyrazole, sequential catalytic C4 arylation, dechlorination, catalytic C5 arylation reactions allowed the synthesis of a 4,5-diarylated pyrazole derivative.