Development of Bifunctional Ligands for Efficient Selective Activation of Simple Arenes

本研究开发了一种新型的“屋顶”配体Bpin-SpiroBpy，用于简单芳烃的间位选择性C-H活化。铱催化的各种单取代芳烃的C-H硼化反应证实了这一概念，在铱催化的硼化反应中，“屋顶”空间上保护了邻位以外最远的帕拉，实现了间位选择性的C-H活化。该策略被证明是通用的，并且各种单取代的芳烃包括烷基苯、苯胺、保护酚和药物分子可以在Meta位以高产率和选择性被选择性地硼化。“屋顶”的选择似乎也很重要。研究发现，三维扩展的SpiroBpy配体上Bpin基团的刚性有效地形成了一个分子口袋，使底物只能以Meta取向接近催化中心。在随后的研究中，发现SpiroBpy配体大大促进了富电子芳烃的铱C-H硼化反应。以1，3-二甲氧基苯和1，3-二叔丁基苯等富电子芳烃为底物，以SpiroBpy为配体，铱催化HBpin的C-H硼化反应，得到了高产率的硼化产物。与此相反，在类似条件下，用常用的配体（dtbpy或tmphen）进行硼基化反应的产率较低。该方法有望将该反应的工具箱扩展到更多样化的应用。

In this research, a novel “roof” ligand Bpin-SpiroBpy was developed for the meta-selective C-H activation of simple arenes. This concept was proved by iridium-catalyzed C-H borylation reaction of various kinds of mono-substituted arenes, in which the “roof” sterically protects the remotest para site besides the ortho site to achieve meta-selective C-H activation in the iridium-catalyzed borylation. The strategy proved general, and a variety of monosubstituted arenes including alkylbenzenes, anilines, protected-phenols, and drug molecules could be selectively borylated at the meta position in both high yields and selectivity. The choice of “roof” also appeared to be important. It was found that the rigidness of Bpin group on the three-dimensionally expanded SpiroBpy ligand effectively created a molecular pocket that accommodates the substrate approaching the catalytic center only in the meta orientation.In the following investigations, it was found that the iridium C-H borylation of electron-rich arenes was largely boosted by employing SpiroBpy as the ligand. When electron-rich arenes such as 1,3-dimethoxybenzene and 1,3-di-tert-butylbenzene were used as the substrate for the iridium-catalyzed C-H borylation with HBpin, the borylated product was obtained in high yields by using SpiroBpy as the ligand. In contrast, the borylation proceeded in lower yields with the commonly used ligands (dtbpy or tmphen) under similar conditions. This method is expected to expand the toolbox of this reaction to more diverse applications.