Carbanions for synthesis by photoinduced sequential multi-electron transfer

通过光诱导连续多电子转移合成碳负离子

• 批准号: 361478827
• 负责人: Professor Dr. Burkhard König
• 金额: --
• 依托单位: Institut für Organische Chemie
• 依托单位国家: 德国
• 项目类别: Reinhart Koselleck Projects
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/361478827?language=en
• 关键词: Carbanions; synthesis; photoinduced; sequential; multi

Visible light photoredox catalysis has developed into a valuable method for organic synthesis over the last decade. The key step is the photo-induced transfer of one electron from a redox active photocatalyst to a substrate triggering its chemical conversion. In most cases radical reactions are initiated, which limits a broader application in organic synthesis.The aim of this project is to extend visible light photoredox catalysis to ionic reactions, particular to the in situ generation of carbanions. Carbanions are key intermediates in synthesis and one typical preparation is the reduction of organohalides with metals, such as magnesium giving Grignard reagents. Using metals as the stoichiometric electron donor is energy intensive and generates pyrophoric intermediates although the metal is not retained in the final organic product. Replacing metal reduction by visible light induced multi-electron transfer should allow the in situ preparation of carbon nucleophiles with unprecedented energy efficiency at mild reaction conditions. A new carbanion chemistry without metals may be imagined. To achieve this goal, we use our previously established method accumulating the energy of two visible light photons generating strongly reductive potentials. Stepwise direct or mediated photo-induced transfer of two electrons combined with the loss of an anionic leaving group or protonation converts organohalides or alkenes, respectively, into their corresponding carbanions.

在过去的十年中，可见光光氧化还原催化已发展成为一种有价值的有机合成方法。关键步骤是一个电子从氧化还原活性光催化剂到基材的光诱导转移，从而触发其化学转化。在大多数情况下会引发自由基反应，这限制了在有机合成中更广泛的应用。该项目的目的是将可见光光氧化还原催化扩展到离子反应，特别是碳负离子的原位生成。碳负离子是合成中的关键中间体，一种典型的制备方法是用金属（例如镁）还原有机卤化物，得到格氏试剂。使用金属作为化学计量的电子供体是能源密集型的，并且会产生自燃中间体，尽管金属不会保留在最终的有机产物中。用可见光诱导的多电子转移代替金属还原应该可以在温和的反应条件下以前所未有的能量效率原位制备碳亲核试剂。可以想象一种没有金属的新碳负离子化学。为了实现这一目标，我们使用之前建立的方法累积两个可见光光子的能量，产生强还原势。两个电子的逐步直接或介导的光诱导转移与阴离子离去基团的损失或质子化相结合，分别将有机卤化物或烯烃转化为其相应的碳负离子。