HCO₃^--mediated highly efficient photoelectrochemical dioxygenation of arylalkenes: triple roles of HCO₃^--derived radicals

Alkene dioxygenation reactions are significant organic transformation process, but the direct oxidation of alkenes on photoanodes exhibits quite poor yields for dioxygenation products. Here, we report that the presence of bicarbonate in a heterogenous photoelectrochemical (PEC) cell can achieve efficient dioxygenation of alkenes under mild conditions. A broad range of alkene substrates with a variety of substitute groups can be effectively oxygenated to diols or alpha-hydroxy ketones, with a product yield of up to 89%. Furthermore, we identified that the diol product is formed via a peroxydiol intermediate. Spin-trap electron paramagnetic resonance (EPR) experiments show that the HCO3--derived radicals are important active species. Accordingly, we propose a triple role for formed HCO3--derived radicals in the dioxygenation of alkenes: attacking the CC bond of the alkene to initiate the reaction, producing (CO4-)-C-center dot active species for the formation of a peroxydiol intermediate, and reducing the peroxydiol to a diol. The present work provides a promising strategy for the transformation of alkenes with green radicals and paves the way for the application of HCO3- in PEC organic synthesis.