Heterocyclic compounds having a nitrogen atom in the ring exhibit very interesting biological activities. Indole is the core structure of many bioactive compounds owing to its high affinity to bind with most biological targets. Indole is an electron-rich compound and generally prefers electrophilic rather than nucleophilic substitution. Hence, many important indole derivatives are difficult to synthesize through the conventional reactivity of indole. This limitation can be avoided by using the umpolung, from the German word meaning polarity inversion. In umpolung, the indole molecule, especially the C2 and C3 positions, behave as an electrophile. As C2-functionalized indoles have substantial importance in synthetic and pharmaceutical chemistry, this review focuses on the C2 umpolung of indoles via the indirect approach which is less explored. Unlike direct approaches of indole umpolung, indirect methods have several advantages and therefore a number of research articles have been published in this field. But no review is available up till now. This is the first review on this topic and we believe that it will surely motivate the readers to work in this area further.

中文翻译：

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经由Umpolung的吲哚的C 2-官能化的最新进展。

环中具有氮原子的杂环化合物表现出非常有趣的生物学活性。吲哚是许多生物活性化合物的核心结构，这是由于其与大多数生物靶标的高亲和力。吲哚是一种富电子的化合物，通常更倾向于亲电子取代而不是亲核取代。因此，许多重要的吲哚衍生物很难通过常规的吲哚反应来合成。通过使用umpolung（来自极性相反的德语单词）可以避免此限制。在化合物中，吲哚分子，特别是C2和C3位置，表现为亲电子试剂。由于C2官能化的吲哚在合成和药物化学中具有重要意义，因此本文将通过较少探讨的间接方法来重点研究吲哚的C2负载。与吲哚的直接方法不同，间接方法具有许多优点，因此该领域已发表了许多研究文章。但是到目前为止，尚无任何评论。这是该主题的第一篇评论，我们相信它将肯定会激发读者进一步在这一领域开展工作。