Mechanistic insights and kinetic analysis for the oxidative hydroxylation of arylboronic acids by visible light photoredox catalysis: a metal-free alternative.

The photocatalytic hydroxylation of boronic acids with methylene blue as photosensitizer proceeds with high efficiency. Detailed time-resolved studies of the relevant rate constants provide a clear mechanistic understanding of excited-state processes and guided the selection of the photocatalyst and the optimization of experimental conditions.