KINETICS AND MECHANISM OF AMINIUM SALT INITIATED CYCLOADDITIONS
KINETICS AND MECHANISM OF AMINIUM SALT INITIATED CYCLOADDITIONS
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DOI：
10.1021/ja00238a027
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发表时间：
1987-02-18
影响因子：
15
通讯作者：
BAULD, NL
中科院分区：
文献类型：
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作者：
LORENZ, KT;BAULD, NL
研究了铵盐引发环加成反应的动力学，验证了以前提出的阳离子-自由基链反应机理。温度依赖性的研究提供了第一个实验测量的阳离子自由基/中性环加成的活化参数。与理论计算一致，这些反应具有非常低的活化能（< 5 kcal/mol）。添加三羟甲基氨基甲烷引起的速率阻滞观察到（4-溴苯基）胺对于阳离子-自由基链机理是特异性的，与之相反，例如，在本实验室中，三芳基铵盐对各种Diels-Alder反应和环丁烷化反应都有很强的催化/引发作用[1] 4 567，并根据阳离子自由基链机理进行了解释。1，5这些相同的环加成反应中的大多数可以在众所周知的产生阳离子自由基的光敏电子转移（PET）条件下完成，这一观察结果为这一机理建议提供了强有力的支持。6，7铵盐和PET诱导的反应表现出显著的
The kinetics of aminium salt initiated cycloadditions has been studied and the previously proposed cation-radical chain mechanism verified. Temperature-dependence studies have provided the first experimental measurements of activation parameters for cation radical/neutral cycloadditions. Consistent with theoretical calculations, these reactions have extraordinarily low (< 5 kcal/mol) activation energies. The rate retardation engendered by added tris (4-bromophenyl) amine is observed to be specific for cation-radical chain mechanisms, as opposed to, eg, Bronsted acid-catalyzed mechanisms and is proposed as a general kinetic criterionfor the cation-radical chain mechanism.Potent catalysis/initiation of a variety of Diels-Alder and cy-clobutanation reactions by triarylaminium salts has been observed in this laboratory1" 4 567and interpreted in terms of a cation-radical chain mechanism. 1, 5 The observation that most of these same cycloadditions can be accomplished under photosensitized elec-tron-transfer (PET) conditions well-known to generate cation radicals lends strong support to this mechanistic proposal. 6, 7 The aminium salt and PET-induced reactions exhibit remarkable