Carbanions for synthesis by photoinduced sequential multi-electron transfer

可见光光氧化还原催化是近十年来发展起来的一种有价值的有机合成方法。关键步骤是光诱导一个电子从氧化还原活性光催化剂转移到底物，引发其化学转化。本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量密集的，并且产生自燃中间体，尽管金属不保留在最终的有机产物中。用可见光诱导的多电子转移取代金属还原，可以在温和的反应条件下原位制备具有前所未有的能量效率的碳亲核试剂。可以设想一种不含金属的新碳负离子化学。为了实现这一目标，我们使用我们以前建立的方法，积累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结合阴离子离去基团的损失或质子化分别将有机卤化物或烯烃转化为它们相应的碳负离子。

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.