Carbanions for synthesis by photoinduced sequential multi-electron transfer

近十年来，可见光氧化还原催化已发展成为一种有价值的有机合成方法。关键的一步是光诱导一个电子从氧化还原活性光催化剂转移到底物上，触发其化学转化。在大多数情况下，自由基反应被引发，这限制了其在有机合成中的广泛应用，本项目的目的是将可见光氧化还原催化扩展到离子反应，特别是原位生成碳负离子。碳离子是合成中的关键中间体，典型的制备方法之一是有机卤化物与金属的还原，如给出格氏试剂的镁。使用金属作为化学计量电子供体是能量密集型的，并产生自燃中间体，尽管金属不保留在最终的有机产品中。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。可以想象一种新的不含金属的碳负离子化学。为了实现这一目标，我们使用我们先前建立的方法来积累产生强还原势的两个可见光光子的能量。两个电子的分步直接或介导光诱导转移，结合阴离子离开基团的损失或质子化，分别将有机卤化物或烯烃转化为相应的碳负离子。

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.