Mechanistic Investigations into the Cation Radical Newman-Kwart Rearrangement
Mechanistic Investigations into the Cation Radical Newman-Kwart Rearrangement
复制标题
DOI：
10.1021/acscatal.9b00465
复制
发表时间：
2019-05-01
期刊：
影响因子：
12.9
通讯作者：
Nicewicz, David A.
中科院分区：
文献类型：
--
作者：
Cruz, Cole L.;Nicewicz, David A.
本文描述了阳离子自由基纽曼-沃特重排的控制因素。通过光谱分析和动力学分析，表明反应中间体是一个具有显著硫基自由基特征的硫酮阳离子自由基。这种中间体经历了类似的化学反应，如烯烃立体突变，这与用其他方法产生的硫基自由基是一样的。此外，动力学研究表明，在该体系中观察到的电子依赖性是硫酮阳离子自由基的限速分子内亲核俘获的结果。重要的是，反应中间体的噻基自由基特征可以用来合理化所有的反应观察。这一机制模型与观察到的高稀释率下的速率增强是一致的，它减少了非循环中间体的形成。设计了一个热化学循环来预测哪些底物最容易经历阳离子自由基介导的重排。
Efforts to elucidate the governing factors in the cation radical Newman-Kwart rearrangement are described. Through a combination of spectroscopic and kinetic analyses, it has been shown that the reactive intermediate is a thione cation radical that has' significant thiyl radical character. This intermediate undergoes similar chemistry, such as olefin stereomutation, that has been observed for thiyl radicals generated by other means. Moreover, kinetic studies demonstrate that the electronic dependence observed in the system is the result of rate-limiting intramolecular nucleophilic trapping of the thione cation radical. Importantly, the thiyl radical character of the reactive intermediate can be used to rationalize all reaction observations. This mechanistic model is in line with observed rate enhancement at higher dilutions that decreases the formation of an off-cycle intermediate. A thermochemical cycle was devised to predict which substrates will most easily undergo the cation-radical-mediated rearrangement.