Structural basis for regioisomerization in the alkali-metal-mediated zincation (AMMZn) of trifluoromethyl benzene by isolation of kinetic and thermodynamic intermediates.
Structural basis for regioisomerization in the alkali-metal-mediated zincation (AMMZn) of trifluoromethyl benzene by isolation of kinetic and thermodynamic intermediates.
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DOI：
10.1021/ja1038598
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发表时间：
2010-07-14
影响因子：
15
通讯作者：
Russo, Luca
中科院分区：
文献类型：
--
作者：
Armstrong, David R.;Blair, Victoria L.;Clegg, William;Dale, Sophie H.;Garcia-Alvarez, Joaquin;Honeyman, Gordon W.;Hevia, Eva;Mulvey, Robert E.;Russo, Luca
为了加深对碱金属介导的锌化的结构和机制的了解，本研究监测了 TMP-二烷基锌酸盐试剂 [(TMEDA)Na(TMP)(tBu)Zn(tBu)] 1 和三氟甲基苯 C6H5CF32 之间的反应。在室温下观察到产物的复杂混合物。 X射线晶体学鉴定出其中两种产物分别为异三阴离子[(TMEDA)Na(TMP)(C6H4-CF3)Zn(tBu)]的邻位和间位区域异构体，分别为3-邻位和3-间位。块状结晶产物的多核NMR数据证实了这两种区域异构体以及第三种异构体3-对的存在，其比例分别为20:11:1，以及另外的产物4，其也表现出芳基底物的邻位锌化。在 0 °C 重复反应仅得到 4，其晶体学特征为 [{(TMEDA)2Na}+{Zn(C6H4-CF3)(tBu)2}−]。模仿最初的室温反应，该动力学产物随后与 TMP(H) 反应，得到复杂的产物混合物，其中明显包括 3 的三种区域异构体。令人惊讶的是，4 采用溶剂分离的离子对排列，与 3-邻位和 3-间位的接触离子变体形成对比。借助模型系统的 DFT 计算，讨论的重点是这些反应中表现出的不同碱度、酰胺基或烷基和步骤，以及这些分离的关键金属中间体（在任何亲电拦截步骤之前）内的结构和键合，特别是涉及碱金属的相互作用，如何影响 Zn−H 交换过程的区域选择性。
Performed with a desire to advance knowledge of the structures and mechanisms governing alkali-metal-mediated zincation, this study monitors the reaction between the TMP-dialkylzincate reagent [(TMEDA)Na(TMP)(tBu)Zn(tBu)] 1 and trifluoromethyl benzene C6H5CF32. A complicated mixture of products is observed at room temperature. X-ray crystallography has identified two of these products as ortho- and meta-regioisomers of heterotrianionic [(TMEDA)Na(TMP)(C6H4-CF3)Zn(tBu)], 3-ortho and 3-meta, respectively. Multinuclear NMR data of the bulk crystalline product confirm the presence of these two regioisomers as well as a third isomer, 3-para, in a respective ratio of 20:11:1, and an additional product 4, which also exhibits ortho-zincation of the aryl substrate. Repeating the reaction at 0 °C gave exclusively 4, which was crystallographically characterized as [{(TMEDA)2Na}+{Zn(C6H4-CF3)(tBu)2}−]. Mimicking the original room-temperature reaction, this kinetic product was subsequently reacted with TMP(H) to afford a complicated mixture of products, including significantly the three regioisomers of 3. Surprisingly, 4 adopts a solvent-separated ion pair arrangement in contrast to the contacted ion variants of 3-ortho and 3-meta. Aided by DFT calculations on model systems, discussion focuses on the different basicities, amido or alkyl, and steps, exhibited in these reactions, and how the structures and bonding within these isolated key metallic intermediates (prior to any electrophilic interception step), specifically the interactions involving the alkali metal, influence the regioselectivity of the Zn−H exchange process.
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影响因子：
4.9
作者：
Conway, Ben;Graham, David V.;Mulvey, Robert E.
通讯作者：
Mulvey, Robert E.
影响因子：
4.3
作者：
Deacon, Glen B.;Forsyth, Craig M.;Wang, Jun
通讯作者：
Wang, Jun
影响因子：
4.3
作者：
Clegg, William;Conway, Ben;Graham, David V.;Hevia, Eva;Kennedy, Alan R.;Mulvey, Robert E.;Russo, Luca;Wright, Dominic S.
通讯作者：
Wright, Dominic S.
影响因子：
56.9
作者：
Kennedy, Alan R.;Klett, Jan;Wright, Dominic S.
通讯作者：
Wright, Dominic S.
影响因子：
4.3
作者：
Armstrong, David R.;Garcia-Alvarez, Joaquin;Mulvey, Robert E.
通讯作者：
Mulvey, Robert E.