Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warsaw (Poland).
Angew Chem Int Ed Engl. 2013 Sep 16;52(38):9900-30. doi: 10.1002/anie.201210238. Epub 2013 Jul 14.
Does the dehydrogenative coupling of aromatic compounds mediated by AlCl3 at high temperatures and also by FeCl3, MoCl5, PIFA, or K3[Fe(CN)6] at room temperature proceed by the same mechanism in all cases? With the growing importance of the synthesis of aromatic compounds by double C-H activation to give various biaryl structures, this question becomes pressing. Since some of these reactions proceed only in the presence of non-oxidizing Lewis acids and some only in the presence of certain oxidants, the authors venture the hypothesis that, depending on the electronic structure of the substrates and the nature of the "catalyst", two different mechanisms can operate. One involves the intermediacy of a radical cation and the other the formation of a sigma complex between the acid and the substrate. The goal of this Review is to encourage further mechanistic studies hopefully leading to an in-depth understanding of this phenomenon.
由 AlCl3 在高温下以及由 FeCl3、MoCl5、PIFA 或 K3[Fe(CN)6] 在室温下介导的芳香族化合物的脱氢偶联是否在所有情况下都通过相同的机制进行？随着通过双重 C-H 活化合成芳香族化合物以获得各种联苯结构的重要性不断增加，这个问题变得紧迫。由于这些反应中的一些仅在非氧化路易斯酸的存在下进行，而另一些仅在某些氧化剂的存在下进行，因此作者推测，取决于底物的电子结构和“催化剂”的性质，可以操作两种不同的机制。一种涉及自由基阳离子的中间体，另一种涉及酸和底物之间的 sigma 配合物的形成。这篇综述的目的是鼓励进一步的机理研究，希望能深入了解这一现象。
