Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
J Am Chem Soc. 2010 Nov 17;132(45):16085-93. doi: 10.1021/ja1058789. Epub 2010 Oct 27.
o-Carboryne (1,2-dehydro-o-carborane) has been reported as a very reactive intermediate and regarded as a three-dimensional relative of benzyne, whereas the 1,3-dehydro-o-carborane has remained elusive. In this article, we present the preparation of 1,3-dehydro-o-carborane from 3-iodo-1-lithio-o-carborane mediated by palladium(0). This reactive intermediate can be trapped by alkynes via Pd/Ni-cocatalyzed [2 + 2 + 2] cycloaddition reaction, leading to the formation of C,B-substituted-o-carborane derivatives. The possible reaction mechanism involving the formation of metal-1,3-dehydro-o-carborane followed by stepwise insertions of 2 equiv of alkyne and reductive elimination is proposed, and the relative reactivity of M-C versus M-B bond in metal-1,3-dehydro-o-carborane complexes is also discussed. This work offers a new methodology for B-functionalization of carboranes and demonstrates that metal-1,3-dehydro-o-carborane can be viewed as a new kind of boron nucleophile.
o-卡宾（1,2-去氢-o-卡硼烷）已被报道为一种非常活泼的中间体，被认为是苯炔的三维类似物，而 1,3-去氢-o-卡硼烷则一直难以捉摸。在本文中，我们报告了由钯(0)介导的 3-碘-1-锂代-o-卡硼烷制备 1,3-去氢-o-卡硼烷。这种反应性中间体可以通过钯/镍协同催化的[2 + 2 + 2]环加成反应与炔烃发生捕获，生成 C，B-取代的-o-卡硼烷衍生物。提出了涉及金属-1,3-去氢-o-卡硼烷形成的可能反应机制，随后是 2 当量炔烃的逐步插入和还原消除，还讨论了金属-1,3-去氢-o-卡硼烷配合物中 M-C 与 M-B 键的相对反应性。这项工作为卡硼烷的 B 官能化提供了一种新方法，并证明金属-1,3-去氢-o-卡硼烷可以看作是一种新型的硼亲核试剂。
