Department of Chemistry, Faculty of Science , Tokyo University of Science , 1-3 Kagurazaka, Shinjuku-ku , Tokyo 162-8601 , Japan.
J Am Chem Soc. 2019 Oct 30;141(43):17042-17047. doi: 10.1021/jacs.9b06910. Epub 2019 Sep 18.
The metal-catalyzed ()-selective hydroboration of terminal alkynes is synthetically challenging due to the usually ()-selective nature of the hydroboration and the formation of the thermodynamically unstable ()-isomer. Herein, we report that N-heterocyclic-carbene-ligated ruthenium complexes catalyze the ()-selective hydroboration of terminal alkynes with H-B(dan) (dan = naphthalene-1,8-diaminato), which generates a diverse range of synthetically valuable ()-alkenylboranes. Mechanistic studies, particularly the isolation of a catalytically relevant borylruthenium complex, revealed a mechanism that involves the insertion of the alkyne into a Ru-B bond, which provides a catalytic cycle that is distinctly different from that of previously reported ()-selective hydroborations. The direct cross-coupling of the obtained ()-alkenyl-B(dan) enables the rapid synthesis of biologically active Combretastatin A-4 analogues.
由于硼氢化反应通常具有（顺式）选择性，并且热力学上不稳定的（反式）异构体容易形成，因此金属催化的末端炔烃（顺式）选择性硼氢化反应在合成上具有挑战性。在此，我们报告氮杂环卡宾配位的钌配合物可以催化末端炔烃与 H-B(dan)（dan = 萘-1,8-二胺）的（顺式）选择性硼氢化反应，生成一系列具有合成价值的（顺式）烯基硼烷。机理研究，特别是催化相关的硼基钌配合物的分离，揭示了一种涉及炔烃插入 Ru-B 键的机理，这提供了一种与先前报道的（顺式）选择性硼氢化反应明显不同的催化循环。所得到的（顺式）烯基-B(dan)可以直接进行交叉偶联，从而快速合成具有生物活性的 Combretastatin A-4 类似物。
