A meta-selective C–H borylation directed by a secondary interaction between ligand and substrate
作者:Yoichiro Kuninobu、Haruka Ida、Mitsumi Nishi、Motomu Kanai
DOI:10.1038/nchem.2322
日期:2015.9
Regioselective CâH bond transformations are potentially the most efficient method for the synthesis of organic molecules. However, the presence of many CâH bonds in organic molecules and the high activation barrier for these reactions make these transformations difficult. Directing groups in the reaction substrate are often used to control regioselectivity, which has been especially successful for the ortho-selective functionalization of aromatic substrates. Here, we describe an iridium-catalysed meta-selective CâH borylation of aromatic compounds using a newly designed catalytic system. The bipyridine-derived ligand that binds iridium contains a pendant urea moiety. A secondary interaction between this urea and a hydrogen-bond acceptor in the substrate places the iridium in close proximity to the meta-CâH bond and thus controls the regioselectivity. 1H NMR studies and control experiments support the participation of hydrogen bonds in inducing regioselectivity. Reversible direction of the catalyst through hydrogen bonds is a versatile concept for regioselective CâH transformations. Directing groups in a substrate are frequently used to direct the regioselectivity of CâH activation reactions. Now it has been shown that regioselectivity can be directed by a ligand, which binds to both the catalysing metal centre and a distal hydrogen-bond acceptor in the substrate. This secondary interaction places the metal in close proximity to the reacting CâH bond.
区域选择性C-H键转化可能是合成有机分子最有效的方法。然而,由于有机分子中存在许多C-H键以及这些反应的高活化能障碍,这些转化变得困难。反应底物中常常使用导向基团来控制区域选择性,这在芳香族底物的邻位选择性功能化方面取得了特别成功。在此,我们描述了一种使用新设计的催化体系对芳香化合物进行铱催化间位选择性C-H硼化的方法。与铱配位的双吡啶衍生物配体含有一个悬挂的脲部分。该脲与底物中氢键受体之间的次级相互作用使得铱靠近间位C-H键,从而控制了区域选择性。1H核磁共振研究和对照实验支持氢键在诱导区域选择性中的参与。通过氢键的可逆导向催化剂是区域选择性C-H转化的一个多功能概念。底物中的导向基团经常被用来引导C-H活化反应的区域选择性。现在已证明,配体可以通过与催化金属中心和底物中远端的氢键受体结合来导向区域选择性。这种次级相互作用使得金属靠近反应的C-H键。