Flow Chemistry Group, van 't Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
PhotoGreen Lab, Department of Chemistry, University of Pavia, viale Taramelli 12, 27100 Pavia, Italy.
J Am Chem Soc. 2023 Jan 18;145(2):991-999. doi: 10.1021/jacs.2c10444. Epub 2022 Dec 30.
Herein, we present a comprehensive study on the use of -heterocyclic carbene (NHC)-ligated boryl radicals to enable C(sp)-C(sp) bond formation under visible-light irradiation via Halogen-Atom Transfer (XAT). The methodology relies on the use of an acridinium dye to generate the boron-centered radicals from the corresponding NHC-ligated boranes via single-electron transfer (SET) and deprotonation. These boryl radicals subsequently engage with alkyl halides in an XAT step, delivering the desired nucleophilic alkyl radicals. The present XAT strategy is very mild and accommodates a broad scope of alkyl halides, including medicinally relevant compounds and biologically active molecules. The key role of NHC-ligated boryl radicals in the operative reaction mechanism has been elucidated through a combination of experimental, spectroscopic, and computational studies. This methodology stands as a significant advancement in the chemistry of NHC-ligated boryl radicals, which had long been restricted to radical reductions, enabling C-C bond formation under visible-light photoredox conditions.
在此，我们进行了一项综合性研究，探讨了利用 -杂环卡宾（NHC）配位的硼基自由基通过可见光照射下的卤原子转移（XAT）实现 C(sp)-C(sp) 键形成。该方法依赖于吖啶鎓染料通过单电子转移（SET）和去质子化作用，将相应的 NHC 配位硼烷转化为硼中心自由基。这些硼基自由基随后在 XAT 步骤中与烷基卤化物反应，生成所需的亲核烷基自由基。本 XAT 策略非常温和，可容纳广泛的烷基卤化物，包括具有医学相关性的化合物和生物活性分子。通过实验、光谱和计算研究的结合，阐明了 NHC 配位的硼基自由基在操作反应机制中的关键作用。该方法是 NHC 配位的硼基自由基化学的重大进展，长期以来，这些自由基仅限于自由基还原反应，而本方法可在可见光光还原条件下实现 C-C 键形成。
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