Superelectrophilic intermediates in nitrogen-directed aromatic borylation.
Superelectrophilic intermediates in nitrogen-directed aromatic borylation.
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DOI：
10.1021/ja905369n
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发表时间：
2009-10-21
影响因子：
15
通讯作者：
Vedejs, Edwin
中科院分区：
文献类型：
--
作者：
De Vries, Timothy S.;Prokofjevs, Aleksandrs;Harvey, Jeremy N.;Vedejs, Edwin
描述了在由氢桥硼阳离子产生硼离子的条件下硼化的第一个例子。可观察到的氢桥阳离子是通过使用 Ph3C+ (C6F5)4B− (TrTPFPB) 作为氢化物受体从 N,N-二甲胺硼烷 Ar(CH2)nNMe2BH3 中提取氢化物而生成的。在过量 TrTPFPB 存在下，氢桥阳离子发生内部硼化，得到 n = 1-3 的环胺硼烷衍生物。在 Ar = C6H5 和 n = 1 的情况下，根据还原猝灭实验以及 11B 和 1H NMR 光谱，产物形成为相应的环状硼离子。同样的环状硼离子也可以通过脱甲硅烷基作用从 Ar = o-C6H4SiMe3 的底物中形成，但 Ar = o-C6H4CMe3 的类似系统提供了独特的 保留叔丁基取代基的环化产物。邻位氘化底物经历环化，其产物决定同位素效应为 kH/kD 2.8。已使用 B3LYP/6-31G* 方法评估了潜在的阳离子中间体。计算表明，14a 的内部硼基化是通过 C–H 插入过渡态发生的，该过渡态可以从硼 π 配合物或从具有几乎相同能量的 Wheland 中间体进入。 Ar = o-C6H4SiMe3 示例强烈有利于 Wheland 中间体的形成，并且通过内部 SiMe3 从碳迁移到与硼相连的氢化物之一来发生脱甲硅烷基化。
The first examples of borylation under conditions of borenium ion generation from hydrogen-bridged boron cations are described. The observable H-bridged cations are generated by hydride abstraction from N,N-dimethylamine boranes Ar(CH2)nNMe2BH3 using Ph3C+ (C6F5)4B− (TrTPFPB) as the hydride acceptor. In the presence of excess TrTPFPB, the hydrogen-bridged cations undergo internal borylation to afford cyclic amine borane derivatives with n = 1-3. The products are formed as the corresponding cyclic borenium ions according to reductive quenching experiments and 11B and 1H NMR spectroscopy in the case with Ar = C6H5 and n = 1. The same cyclic borenium cation is also formed from the substrate with Ar = o-C6H4SiMe3 via desilylation, but the analogous system with Ar = o-C6H4CMe3 affords a unique cyclization product that retains the tert-butyl substituent. An ortho-deuterated substrate undergoes cyclization with a product-determining isotope effect of kH/kD 2.8. Potential cationic intermediates have been evaluated using B3LYP/6-31G* methods. The computations indicate that internal borylation from 14a occurs via a C–H insertion transition state that is accessible from either the borenium π complex or from a Wheland intermediate having nearly identical energy. The Ar = o-C6H4SiMe3 example strongly favors formation of the Wheland intermediate, and desilylation occurs via internal SiMe3 migration from carbon to one of the hydrides attached to boron.
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影响因子：
15
作者：
BERLINER, E
通讯作者：
BERLINER, E
影响因子：
16.6
作者：
Chase, Preston A.;Stephan, Douglas W.
通讯作者：
Stephan, Douglas W.
影响因子：
4.6
作者：
ALLAOUD, S;FRANGE, B
通讯作者：
FRANGE, B
影响因子：
4.6
作者：
BENJAMIN, LE;CARVALHO, DA;TAKACS, EA
通讯作者：
TAKACS, EA
DOI：
10.1039/jr9580003073
发表时间：
1958-01-01
期刊：
JOURNAL OF THE CHEMICAL SOCIETY
影响因子：
--
作者：
DEWAR, MJS;KUBBA, VP;PETTIT, R
通讯作者：
PETTIT, R