Formation of Reactive π-Conjugated Frustrated N/B Pairs by Borane-Induced Propargyl Amine Rearrangement.
Formation of Reactive π-Conjugated Frustrated N/B Pairs by Borane-Induced Propargyl Amine Rearrangement.
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DOI：
10.1021/jacs.7b11958
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发表时间：
2018-02
影响因子：
15
通讯作者：
Tongdao Wang;C. Daniliuc;Christian Mück‐Lichtenfeld;G. Kehr;G. Erker
中科院分区：
文献类型：
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作者：
Tongdao Wang;C. Daniliuc;Christian Mück‐Lichtenfeld;G. Kehr;G. Erker
N-丙叉四甲基哌啶与一系列反式-烯基-B(C6F5)2化合物反应，得到取代烯基桥联的受挫N/B Lewis对5。它们的结构和光谱特征表明，它们明显参与了介晶S-反式-亚胺/硼酸-烯烃的共振型。这些化合物被认为是在逐步加成/重排过程中形成的，该过程是由反式-1，2-胺/硼烷FLP加成到碳-碳三键上，生成反应性两性离子氮杂环丙烷/烯基硼酸盐中间体。随后的烯基硼酸盐攻击导致活化的三元杂环的打开，产物5a-c的形成干净。用B(C6F5)3处理炔丙基-TMP底物，得到了一个稳定的氮杂环丙烷/硼酸盐甜菜碱实例，该实例得到了分离和充分的表征。产品5a-c是活性N/B FLP。它们在温和的条件下异相裂解二氢，得到各自的NH+/BH-产物9a-c。这些都含有Z构型的核心C═C双键，这表明在反应过程中围绕5a-c的中心C-C键进行了旋转平衡。通过密度泛函理论计算，分析了5C体系的结构和化学特征。
N-Propargyltetramethylpiperidine reacts with a series of trans-alkenyl-B(C6F5)2 compounds to give the substituted alkenyl-bridged frustrated N/B Lewis pairs 5. Their structures and spectroscopic features indicate a pronounced participation of the mesomeric s-trans-iminium/borata-alkene resonance form. The compounds are thought to be formed in a stepwise addition/rearrangement process which is initiated by a trans-1,2-amine/borane FLP addition to the carbon-carbon triple bond to generate a reactive zwitterionic aziridinium/alkenylborate intermediate. Subsequent alkenylborate attack leads to opening of the activated three-membered heterocycle with clean formation of the products 5a-c. Treatment of the propargyl-TMP substrate with B(C6F5)3 gave a stable example of such an aziridinium/borate betaine, which was isolated and amply characterized. The products 5a-c are active N/B FLPs. They split dihydrogen heterolytically under mild conditions to give the respective NH+/BH- products 9a-c. These contain Z-configurated core C═C double bonds, which indicates rotational equilibration around the central C-C bond of 5a-c during this reaction. Structural and chemical features of the 5c system were analyzed by DFT calculations.