Visible-light-mediated β-acylative divergent alkene difunctionalization with Katritzky salt/CO2

Abstract

Multicomponent cross-coupling reactions involving alkenes under visible-light photoredox catalysis have tremendous potential to achieve molecular complexity and modularity from renewable feedstocks in a sustainable manner. Here we disclose two similar yet mechanistically distinct visible-light mediated photoredox-catalyzed, redox-neutral, regioselective dicarbofunctionalization reactions of vinyl arenes through three-component coupling. Acylative carbobenzylation and carbocarboxylation have been achieved successfully where the acyl radical is generated via decarboxylation from the ketocarboxylic acid and undergoes addition regioselectively at the β-position of the vinyl arene to generate a stabilized benzylic radical as a common intermediate. Subsequently, this incipient benzyl radical undergoes two distinct pathways: (a) radical–radical cross-coupling with the benzyl radical which is generated from a Katritzky salt to realize acylative benzylation; (b) reductive radical–polar crossover to react with CO₂ (1.0 atm) for acylative carboxylation. In contrast to the previous reports, the acyl radical undergoes addition regioselectively at the β-position of the vinyl arene and deaminative benzylation takes place at the α-position. Remarkably, an all carbon quaternary center is generated from the corresponding 1,1-diaryl styrenes bypassing all other undesired pathways. This unprecedented acylative carboxylation of alkenes afforded a γ-keto carboxylic acid which is a precursor of γ-amino acids. The reactions are reproducible under sunlight irradiation on a gram scale, which is a step forward in sustainable development.