Photocatalytic Generation of Alkyl Carbanions from Alkenes

Organometallic reagents are routinely used as fundamental building blocks in organic chemistry to rapidly diversify molecular fragments via carbanion intermediates. However the catalytic generation of carbanion equivalents particularly from sp3-hybridized alkyl scaffolds, remains an underdeveloped goal in chemical synthesis. To align with the demands of modern synthetic protocols, a general method for the catalytic generation of alkyl carbanions must operate under benign reaction conditions and access commercially available feedstock chemicals. Alkenes constitute an attractive source of latent alkyl carbanion equivalents, however methods for the conversion of carbon-carbon bonds into carbanions is challenged by the need for precious metals and aggressive stoichiometric reductants. Here we disclose an approach for the controlled generation of 2-electron carbon nucleophiles via single electron reduction of aryl alkenes, facilitated by the highly reducing environment of multiphoton photoredox catalysts. We demonstrate that alkene radical anions engage in catalytic, metal free, intermolecular C-C bond-forming reactions with carbonyl derivatives, in a manner analogous to Grignard reagents. Under this reaction manifold, the alkene can be considered a dicarbanion synthon offering new opportunities for orthogonal diversification. This concept was illustrated by the development of four distinct C-C bond forming reactions with aromatic alkenes: hydroalkoxylation, hydroamidation, aminoalkylation and carboxyaminoalkylation, to generate a range of valuable and complex scaffolds.