Di(indolyl)methanes are widely prevalent in pharmaceuticals, agrochemicals, alkaloids, and natural products. Herein, we report a metal-free method for the uniform synthesis of symmetrical and unsymmetrical 3,3′-DIMs through N-hydroxyphthalimide (NHPI)-catalyzed electrolytic C–H alkylation of indoles via a radical cross-coupling pathway. This simple and practical protocol provides a route to a host of 3,3′-DIMs from indoles and alcohols using water as the sole solvent and without metal contamination. Mechanistic studies suggested that the alcohol substrate was oxidized to a carbon radical via a hydrogen atom transfer (HAT) process jointly mediated by NHPI and the anode oxidation process. Importantly, the present indirect electrochemically mediated radical protocol outperforms the traditional Friedel–Crafts route with a broad substrate scope and functional group tolerance, as well as facile gram-scale synthesis without metal contamination.

中文翻译：

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NHPI催化的吲哚与醇的电化学C-H烷基化通过自由基偶联获得二（吲哚基）甲烷

二（吲哚基）甲烷广泛存在于药物、农用化学品、生物碱和天然产物中。在此，我们报告了一种无金属方法，通过自由基交叉偶联途径通过N-羟基邻苯二甲酰亚胺 (NHPI) 催化的吲哚电解 C-H 烷基化来均匀合成对称和不对称的 3,3'-DIM 。这种简单实用的协议提供了一条从吲哚和醇中获得大量 3,3'-DIM 的途径，使用水作为唯一溶剂，并且没有金属污染。机理研究表明，醇底物通过氧化成碳自由基由NHPI和阳极氧化过程共同介导的氢原子转移（HAT）过程。重要的是，目前的间接电化学介导的自由基方案优于传统的 Friedel-Crafts 路线，具有广泛的底物范围和官能团耐受性，以及在没有金属污染的情况下简便的克级合成。