Visible-Light-Driven Aerobic Photooxidation of Aldehydes to Methyl Esters Catalyzed by Riboflavin Tetraacetate

Riboflavin tetraacetate (RFT) catalyzes the aerobic esterification of para-substituted benzaldehydes to their corresponding methyl esters. The reaction proceeds under visible-light irradiation in MeOH/MeCN in the presence of a Bronsted acid such as HCl. Electron transfer from the in situ formed dimethyl acetal to the photoexcited triplet flavin appears to be a key mechanistic step. The acid catalyzes the formation of the acetal and increases the reduction potential of RFT by protonation. The photocatalyst is regenerated by reaction with atmospheric oxygen, which serves as the terminal oxidant.