Department of Chemistry and State Key Laboratory of Synthetic Chemistry , The Chinese University of Hong Kong , Shatin , NT, Hong Kong , China.
J Am Chem Soc. 2019 Aug 14;141(32):12855-12862. doi: 10.1021/jacs.9b06204. Epub 2019 Jul 23.
A proof-of-principle study of cascade dehydrogenative cross-coupling of carboranyl carboxylic acid with readily available benzamide has been achieved, resulting in the facile synthesis of previously inaccessible carborano-isoquinolinone derivatives in a simple one-pot process, in which two cage B-H, one aryl C-H, and one N-H bond were sequentially activated to construct efficiently new B-C and B-N bonds, respectively. Under suitable reaction conditions, such cascade cyclization can be stopped at the first B-H/C-H cross-coupling step to give a series of α-carboranyl benzamides, suggesting the preferential occurrence of B-C cross-coupling over that of B-N. The carboxylic acid directing group plays a key role in the B-C cross-coupling step, which is then removed through in situ decarboxylation. The CV results combined with control experiments indicate that high-valent Ir(V)-species may be involved in the reaction pathways, which is crucial for such cascade dehydrogenative cross-coupling reactions. The isolation and structural identification of a key intermediate, its controlled transformations, and deuterium labeling experiments support a new Ir-nitrene-mediated amination for B-H/N-H dehydrocoupling.
已经实现了硼酸羧酸与易得的苯甲酰胺的级联脱氢交叉偶联的原理验证研究，在简单的一锅法中，容易地合成了以前无法获得的硼烷异喹啉酮衍生物，其中两个笼状 B-H、一个芳基 C-H 和一个 N-H 键依次被激活，分别有效地构建了新的 B-C 和 B-N 键。在合适的反应条件下，这种级联环化可以在第一个 B-H/C-H 交叉偶联步骤停止，得到一系列α-硼烷苯甲酰胺，表明 B-C 交叉偶联优先于 B-N。羧酸导向基团在 B-C 交叉偶联步骤中起着关键作用，然后通过原位脱羧去除。CV 结果结合控制实验表明，高价 Ir(V)-物种可能参与反应途径，这对于这种级联脱氢交叉偶联反应至关重要。关键中间体的分离和结构鉴定、其控制转化和氘标记实验支持 Ir-氮烯介导的 B-H/N-H 脱氢偶联的新反应途径。
