Department of Chemistry , University of Chicago , Chicago , Illinois 60637 , United States.
Department of Chemistry , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States.
J Am Chem Soc. 2018 Jul 11;140(27):8551-8562. doi: 10.1021/jacs.8b04153. Epub 2018 Jun 27.
Palladium/norbornene (Pd/NBE) cooperative catalysis has emerged as a useful tool for preparing poly substituted arenes; however, its substrate scope has been largely restricted to aryl iodides. While aryl bromides are considered as standard substrates for Pd-catalyzed cross coupling reactions, their use in Pd/NBE catalysis remains elusive. Here we describe the development of general approaches for aryl bromide-mediated Pd/NBE cooperative catalysis. Through careful tuning the phosphine ligands and quenching nucleophiles, ortho amination, acylation and alkylation of aryl bromides have been realized in good efficiency. Importantly, various heteroarene substrates also work well and a wide range of functional groups are tolerated. In addition, the utility of these methods has been demonstrated in sequential cross coupling/ ortho functionalization reactions, consecutive Pd/NBE-catalyzed difunctionalization to construct penta-substituted aromatics and two-step meta functionalization reactions. Moreover, the origin of the ligand effect in ortho amination reactions has been explored through DFT studies. It is expected that this effort would significantly expand the reaction scope and enhance the synthetic potential for Pd/NBE catalysis in preparing complex aromatic compounds.
钯/降冰片烯（Pd/NBE）协同催化已成为制备多取代芳烃的有用工具；然而，其底物范围在很大程度上仅限于芳基碘化物。虽然芳基溴化物被认为是 Pd 催化交叉偶联反应的标准底物，但它们在 Pd/NBE 催化中的应用仍然难以捉摸。在这里，我们描述了开发芳基溴介导的 Pd/NBE 协同催化的一般方法。通过仔细调整膦配体和猝灭亲核试剂，可以有效地实现芳基溴的邻位胺化、酰化和烷基化。重要的是，各种杂芳基底物也能很好地工作，并且可以容忍广泛的官能团。此外，这些方法的实用性已在顺序交叉偶联/邻位官能化反应、连续 Pd/NBE 催化双官能化构建五取代芳烃和两步间位官能化反应中得到了证明。此外，还通过 DFT 研究探讨了邻位胺化反应中配体效应的起源。预计这项工作将显著扩大反应范围，并增强 Pd/NBE 催化在制备复杂芳烃化合物方面的合成潜力。
