Carbanions for synthesis by photoinduced sequential multi-electron transfer

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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.