University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, 510641, People's Republic of China.
J Am Chem Soc. 2020 Jun 17;142(24):10634-10640. doi: 10.1021/jacs.0c04670. Epub 2020 Jun 8.
While phenols are frequent and convenient aryl sources in cross-coupling, typically as sulfonate esters, the direct cross-Ullmann coupling of two different sulfonate esters is unknown. We report here a general solution to this challenge catalyzed by a combination of Ni and Pd with Zn reductant and LiBr as an additive. The reaction has broad scope, as demonstrated in 33 examples (65% ± 11% average yield). Mechanistic studies show that Pd strongly prefers the aryl triflate, the Ni catalyst has a small preference for the aryl tosylate, aryl transfer between catalysts is mediated by Zn, and Pd improves yields by consuming arylzinc intermediates.
虽然酚类是交叉偶联反应中常用且方便的芳基源，通常以磺酸酯的形式存在，但两种不同磺酸酯的直接交叉 Ullmann 偶联反应是未知的。我们在这里报道了一种由 Ni 和 Pd 与 Zn 还原剂以及 LiBr 作为添加剂共同催化的通用解决方案。该反应具有广泛的适用范围，在 33 个实例中得到了证明（平均产率为 65%±11%）。机理研究表明，Pd 强烈倾向于芳基三氟甲磺酸酯，Ni 催化剂对芳基对甲苯磺酸酯略有偏好，芳基在催化剂之间的转移由 Zn 介导，Pd 通过消耗芳基锌中间体来提高产率。
