Phenols are versatile synthetic intermediates and key
structural
motifs in many natural products and biologically active compounds.
We herein report a visible-light-induced aerobic oxidative hydroxylation
of arylboronic acids/pinacol esters using air as oxidant and without
using any catalysts and base, etc., additives, providing a green entry
to a variety of phenols in a highly efficient and concise fashion.
This novel reaction is enabled by photoactivation of an electron donor–acceptor
complex, in which THF serves as both the solvent and electron donor.
DFT studies indicated that the oxidation process involves a concerted
hydrogen abstraction transfer from THF and dehydroxylation of boronic
acid undergoing spin crossover from triplet to singlet to produce
an active peroxoboronic acid intermidiate. Salient merits of this
chemistry include broad substrate scope and excellent functional group
tolerance, gram-scale synthesis, and versatile late-stage functionalizations
as well as the use of air, visible light, and catalyst- and additive-free
conditions. This strategy introduces a novel photoreaction mode with
the aid of a solvent, offering a succinct and environmentally sustainable
route for synthesizing phenols. The strong practicability and highly
efficient access to modifying complex biorelevant molecules bode well
for the potential applications of this chemistry in pharmaceutical
chemistry.