On the Mechanism of Phenolic Formylation Mediated by TiCl<sub>4</sub>Complexes: Existence of Diradical Intermediates Induced by Valence Tautomerism
作者:Carlos Heras、Iván Ramos-Tomillero、Marc Caballero、Marta Paradís-Bas、Ernesto Nicolás、Fernando Albericio、Ibério de P. R. Moreira、Josep Maria Bofill
DOI:10.1002/ejoc.201403548
日期:2015.4
is confirmed by the observed products of phenolic formylation mediated by TiCl4. However, when the nucleophilic path is quenched by appropriate ligand modification, the initial equilibria between the possible neutral complexes of TiCl4 with 3,5-dimethoxyphenol and/or diethyl ether lead to different stable diradical intermediates induced by valence tautomerism that provide valuable activated reagents
Cresp 等人 提出的常规亲电分子内芳香取代途径。[J. 化学 Soc., Perkin Trans。1 1973, 340–345] 由观察到的 TiCl4 介导的酚甲酰化产物证实。然而,当亲核路径通过适当的配体修饰被淬灭时,TiCl4 与 3,5-二甲氧基苯酚和/或乙醚的可能中性络合物之间的初始平衡导致由价互变异构引起的不同稳定双自由基中间体,提供有价值的活化试剂。其中一些物质已被 EPR 检测到,理论上表征并被 TEMPO 捕获,从而为每个苯酚与一个或多个当量 TEMPO 的反应提供了一致的机制。