Visible-light induced disproportionation of pyrrole derivatives for photocatalyst-free aryl halides reduction,Green Chemistry

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Visible-light induced disproportionation of pyrrole derivatives for photocatalyst-free aryl halides reduction
Green Chemistry ( IF 9.3 ) Pub Date : 2020/02/18 , DOI: 10.1039/c9gc04248b
Zhi-Jun Li _{1,

2,

3,

4} , Shuya Li _{1,

3,

4,

5} , Elan Hofman _{1,

2,

3,

4} , Andrew Hunter Davis _{1,

2,

3,

4} , Gyu Leem _{1,

3,

4,

5,

6} , Weiwei Zheng _{1,

2,

3,

4}

Affiliation

As a green synthetic approach, visible light-driven photosynthesis is highly desirable in arylation of inert alkyl halides, as they are important precursors in the total synthesis of natural products and pharmaceuticals. However, the high bond dissociation energy of aryl halides is typically out of the range of a single visible-light photon. Here, we propose an essential initiation and subsequent electron-transfer step process for visible light-driven aryl halide reduction, and identify the key pyrrole radical anion intermediate, that acts as the strong reduction species. We propose a photoinduced disproportionation (PDP) approach without the addition of any photocatalysts or additives to afford radical anions of pyrrole derivatives, which have enough reduction power to transfer an electron to aryl halide, giving rise to the corresponding aryl radical to afford the desired C–H arylated heterocyclic product. Once generated, the heterocyclic product can undergo the same photoinduced disproportionation (PDP) process to activate aryl halides, thereby promoting the reaction rate. This unprecedented initiation step, which was carried out in the absence of photocatalysts and additives under ambient conditions, can also be used for coupling a wide range of (hetero)aryl halides and pyrrole derivatives, as well as the synthesis of drug intermediates and biorelevant compounds.

中文翻译：

可见光诱导的吡咯衍生物歧化以减少无光催化剂的芳基卤化物

作为一种绿色的合成方法，在惰性烷基卤化物的芳基化中，非常需要可见光驱动的光合作用，因为它们是天然产物和药物总合成中的重要前体。但是，芳基卤化物的高键解离能通常超出单个可见光光子的范围。在这里，我们提出了一个重要的引发和随后的电子转移步骤，用于可见光驱动的芳基卤化物还原，并确定了关键的吡咯自由基阴离子中间体，它是强还原物种。我们提出了一种光致歧化（PDP）方法，该方法不添加任何光催化剂或添加剂来提供吡咯衍生物的自由基阴离子，该吡咯衍生物具有足够的还原能力将电子转移至卤代芳基，产生相应的芳基，得到所需的CH芳基化杂环产品。一旦产生，杂环产物可以经历相同的光致歧化（PDP）过程以活化芳基卤化物，从而提高反应速率。这种前所未有的引发步骤是在环境条件下不存在光催化剂和添加剂的情况下进行的，也可用于偶联各种（杂）芳基卤化物和吡咯衍生物，以及合成药物中间体和生物相关化合物。

更新日期：2020-03-24

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