Thallium in organic synthesis. XXIII. Electrophilic aromatic thallation. Kinetics and applications to orientation control in the synthesis of aromatic iodides
Thallium in organic synthesis. XXIII. Electrophilic aromatic thallation. Kinetics and applications to orientation control in the synthesis of aromatic iodides
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有机合成中的铊。
DOI：
10.1021/ja00748a030
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发表时间：
1971
影响因子：
15
通讯作者：
J. D. Hunt
中科院分区：
文献类型：
--
作者：
E. Taylor;F. Kienzle;R. Robey;A. Mckillop*;J. D. Hunt
芳香族铊化反应是一种可逆的亲电取代反应，活化能为 27 kcal/mol，需要较大的空间位阻。添加碘化钾水溶液后发生铊化反应的过程代表了芳香族碘化合物的简单易行的合成，并且控制铊化（进而控制碘化）位置的因素（动力学、热力学、空间）已被系统地探索。间位取代是在热力学控制条件下实现的。在动力学控制的条件下，当试剂（三氟乙酸铊 (III)，TTFA）与定向取代基螯合时，会产生邻位取代，从而允许分子内传递亲电子试剂；而当不存在这种能力时，则会产生对位取代。因此，适当控制条件可以控制同一亲电取代反应中的方向（邻位、间位或对位）。描述了这些观察结果在许多芳香族碘化合物的选择性合成中的应用。
Aromatic thallation is shown to be a reversible, electrophilic substitution reaction with an energy of activation of 27 kcal/mol and a large steric requirement. The process of thallation followed by addition of aqueous potassium iodide represents a simple and facile synthesis of aromatic iodocompounds, and the factors (kinetic, thermodynamic, steric) which control the position of thallation (and hence of iodination) have been systematically explored. Meta substitution is achievedunder conditions of thermodynamic control. Under conditions of kinetic control, ortho substitution results when chelation of the reagent (thallium (III) trifluoroacetate, TTFA) with the directing substituent permits intramolecular delivery of the electrophile, and para substitution results when such capabilities are absent. Thus appropriate manipulation of conditions can lead to control over orientation (ortho or meta or para) in the same electrophilic substitution reaction. The application of these observations to the selec-tive synthesis of a number of aromatic iodo compounds is described.