Mechanistic Insightinto the Photoinduced DecarboxylativeRadical Addition of Carboxylic Acid to Alkenes in a Two-Molecule PhotoredoxSystem

The detailed mechanism of photoinduced decarboxylative radical addition to alkenes using both the effect of an electron donor (ED)/electron acceptor (EA) and laser flash photolysis in a two-molecule photoredox system was investigated. The concentration of EA^•– played an important role in the photoreaction and could be controlled by varying the concentrations of ED/EA and their identity, which influenced Δ<i>G</i>_PET. Higher concentrations of ED/EA and a larger negative Δ<i>G</i>_PET led to a higher concentration of EA^•–, thereby increasing the yield of the adduct; however, the large negative Δ<i>G</i>_PET for the generation of the EDA complex hindered decarboxylation. The two-molecule photoredox system is simple and can be easily tuned by adjusting the concentrations and type (Δ<i>G</i>_PET) of ED/EA through a simple replacement of ED/EA, which is easier than modulating the oxidation/reduction potential in one-molecule photoredox systems.