Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.
Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto, 860-8555, Japan.
Chemistry. 2018 Sep 6;24(50):13223-13230. doi: 10.1002/chem.201801818. Epub 2018 Aug 7.
We recently reported a new one-pot transformation of alkynes into 9,10-diarylphenanthrene derivatives, which proceeds through efficient catalyst-free 1,2-carboboration of alkynes with 9-chloro-9-borafluorene (1 ), which yields a chlorodibenzoborepin, followed by oxidative deborylation/C-C coupling of the resultant chlorodibenzoborepin. Herein, based on new experimental observations for the catalyst-free 1,2-carboboration by using diphenylacetylenes and 1 or 1 as well as results from theoretical investigations, we show how the substituent on the boron atom of 9-borafluorene affects the reactivity toward alkynes. Kinetic studies indicated that the 1,2-carboboration of diphenylacetylene with the borafluorenes can be described as a second-order reaction. The reaction rates became larger with the increase in the acceptor numbers of the borafluorenes (1 >1 >1 ), which was evaluated by the Gutmann-Beckett method based on a Lewis acid/base complexation in solution. Interestingly, thermodynamic parameters obtained experimentally indicated that the term of activation entropy, rather than the term of activation enthalpy, largely contributes to the reaction rate. This experimental result was also supported by DFT calculations. Overall, among the borafluorenes examined, 1 exhibited the highest reactivity toward a wide variety of substituted diarylacetylenes. Similar to the case of chlorodibenzoborepin, when the dibenzoborepin obtained from 1 or 1 was oxidized by using FeCl , an efficient deborylation/C-C coupling took place to give the corresponding 9,10-diarylphenanthrene derivatives in high yields.
我们最近报道了一种炔烃一锅转化为 9,10-二芳基菲衍生物的新方法，该方法通过炔烃与 9-氯-9-硼氟（1）的高效无催化剂 1,2-碳硼化反应进行，生成氯二苯并硼二吡咯，然后通过氧化脱硼/C-C 偶联生成的氯二苯并硼二吡咯。在此，基于无催化剂 1,2-碳硼化反应使用二苯乙炔和 1 或 1 的新实验观察结果以及理论研究结果，我们展示了 9-硼氟烯上的取代基如何影响其对炔烃的反应性。动力学研究表明，二苯乙炔与硼氟的 1,2-碳硼化反应可以描述为二级反应。随着硼氟的接受数（1 >1 >1 ）的增加，反应速率增大，该接受数通过基于路易斯酸碱络合在溶液中的 Gutmann-Beckett 方法进行评估。有趣的是，实验获得的热力学参数表明，活化熵项而不是活化焓项对反应速率有很大贡献。这一实验结果也得到了 DFT 计算的支持。总的来说，在所研究的硼氟中，1 对各种取代的二芳基乙炔表现出最高的反应性。与氯二苯并硼二吡咯的情况类似，当使用 FeCl 氧化 1 或 1 得到的二苯并硼二吡咯时，会发生有效的脱硼/C-C 偶联，以高产率得到相应的 9,10-二芳基菲衍生物。
