Electrochemical synthesis has been rapidly developed over the past few years, while a vast majority of the reactions proceed through a radical pathway. Understanding the properties of radical intermediates is crucial in the mechanistic study of electrochemical transformations and will be beneficial for developing new reactions. Nevertheless, it is rather difficult to determine the “live” radical intermediates due to their high reactivity. In this work, the formation and structure of sulfonamide N-centered radicals have been researched directly by using the time-resolved electron paramagnetic resonance (EPR) technique under electrochemical conditions. Supported by the EPR results, the reactivity of N-centered radicals as a mediator in the hydrogen atom transfer (HAT) approach has been discussed. Subsequently, these mechanistic study results have been successfully utilized in the discovery of an unactivated C(sp³)–H arylation reaction. The kinetic experiments have revealed the rate-determined step is the anodic oxidation of sulfonamides.

中文翻译：

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时间分辨 EPR 揭示了电化学 C(sp3)-H 芳基化反应中 N 中心自由基的形成、结构和反应性

电化学合成在过去几年中得到了迅速发展，而绝大多数反应通过自由基途径进行。了解自由基中间体的性质对于电化学转化的机理研究至关重要，并将有利于开发新的反应。然而，由于它们的高反应性，很难确定“活性”自由基中间体。本工作利用时间分辨电子顺磁共振(EPR)技术在电化学条件下直接研究了磺胺N-中心自由基的形成和结构。在 EPR 结果的支持下，N -中心自由基作为氢原子转移 (HAT) 方法中的介质已被讨论。随后，这些机理研究结果已成功用于发现未活化的 C(sp ³ )-H 芳基化反应。动力学实验表明，速率决定步骤是磺胺类药物的阳极氧化。