Enamine/butadienylborane cycloaddition in the frustrated Lewis pair regime.
Enamine/butadienylborane cycloaddition in the frustrated Lewis pair regime.
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DOI：
10.1039/c5ob01602a
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发表时间：
2015-10
影响因子：
3.2
通讯作者：
Guo-qiang Chen;Fatma Türkyilmaz;C. Daniliuc;Christoph Bannwarth;S. Grimme;G. Kehr;G. Erker
中科院分区：
文献类型：
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作者：
Guo-qiang Chen;Fatma Türkyilmaz;C. Daniliuc;Christoph Bannwarth;S. Grimme;G. Kehr;G. Erker
通过共轭烯炔1a与Piers硼烷[HB（C6 F5）2]的区域选择性炔硼氢化反应制备二烯基硼烷2a。它与一系列苯乙酮衍生的烯胺3反应，导致与硼烷刘易斯酸形成强烯胺β-碳加合物（4）。相比之下，二烯基硼烷2a和一系列大得多的环己酮衍生的烯胺（6）之间的B-C加合物形成在高于约-20 ℃时是快速可逆的。在30 °C下，然后导致形成[4 + 2]环加成产物8。DFT研究表明，该反应可能采取分步路线，通过烯胺加成到二烯基硼烷末端来进行，以产生两性离子硼酸-烯烃/亚胺离子中间体，其经历随后的快速闭环。产物8的加热导致酰胺基硼烷从产物骨架处的邻位氨基/硼烷对消除，得到相应的六氢萘产物10。随后用克里思（2当量）处理导致不饱和环的选择性氧化，得到相应的四氢萘衍生物12。
The dienylborane 2a was prepared by regioselective alkyne hydroboration of the conjugated enyne 1a with Piers' borane [HB(C6F5)2]. Its reaction with a series of acetophenone derived enamines 3 resulted in the formation of the strong enamine β-carbon adduct with the borane Lewis acid (4). In contrast B-C adduct formation between the dienylborane 2a and a series of much more bulky cyclohexanone derived enamines (6) is rapidly reversible above ca.-30 °C and then leads to the formation of the [4 + 2]cycloaddition products 8. A DFT study revealed that this reaction is probably taking a stepwise route, proceeding by means of enamine addition to the dienylborane terminus to generate a zwitterionic borata-alkene/iminium ion intermediate that undergoes rapid subsequent ring closure. Heating of the products 8 led to amidoborane elimination from the vicinal amino/borane pair at the product framework to give the respective hexahydronaphthalene product 10. Subsequent treatment with TEMPO (2 equiv.) resulted in selective oxidation of the unsaturated ring to give the respective tetrahydronaphthalene derivative 12.