External Oxidant-Free Oxidative Cross-Coupling: A Photoredox Cobalt-Catalyzed Aromatic C鈥揌 Thiolation for Constructing C鈥揝 Bonds
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- 作者：Guoting Zhang ; Chao Liu ; Hong Yi ; Qingyuan Meng ; Changliang Bian ; Hong Chen ; Jing-Xin Jian ; Li-Zhu Wu ; Aiwen Lei
- 刊名：Journal of the American Chemical Society
- 出版年：2015
- 出版时间：July 29, 2015
- 年：2015
- 卷：137
- 期：29
- 页码：9273-9280
- 全文大小：626K
- ISSN：1520-5126
文摘
An external oxidant-free oxidative coupling for aromatic C鈥揌 thiolation by visible-light photoredox cobalt-catalysis has been developed. Various substrates could afford benzothiazoles in good to excellent yields, and only H2 is generated as a side product. When catalytic TBAOH was used as the base, not only 2-aryl but also 2-alkylbenzothiazoles could be obtained through this novel dehydrogenative coupling reaction. This method could be scaled up and applied to the synthesis of biologically active molecules bearing benzothiazole structural scaffolds (potent antitumor agents). Furthermore, the unexpected oxidation byproduct amides, which are often generated in oxidative cyclization of thiobenzanilides, can be completely avoided. Mechanistic studies showed that the H2 originates from the substrates. The kinetic studies indicate that the interaction between the cobalt catalyst and proton might be involved in the rate-limiting process.