Photoinduced meta-Selective C-H Oxygenation of Arenes

The merger of photocatalysisand transition-metal catalysis hasrecently emerged as an adaptable platform for the development of innovativeand environmentally benign synthetic methodologies. In contrast toclassical transformation by Pd complexes, photoredox Pd catalysisoperates through a radical pathway in the absence of a radical initiator.Using the synergistic merger of photoredox and Pd catalysis, we havedeveloped a highly efficient, regioselective, and general meta-oxygenation protocol for diverse arenes under mildreaction conditions. The protocol showcases the meta-oxygenation of phenylacetic acids and biphenyl carboxylic acids/alcoholsand is also amenable for a series of sulfonyls and phosphonyl-tetheredarenes, irrespective of the nature and position of the substituents.Unlike thermal C-H acetoxylation which operates through thePd(II)/Pd-IV catalytic cycle, this metallaphotocatalyticC-H activation involves Pd-II/Pd-III/Pd-IV intermediacy. The radical nature of the protocol is establishedthrough radical quenching experiments and EPR analysis of the reactionmixture. Furthermore, the catalytic path of this photoinduced transformationis established through control reactions, absorption spectroscopy,luminescence quenching, and kinetic studies.

Automated summary

The merger of photocatalysis and transition-metal catalysis has led to the development of a versatile platform for environmentally friendly synthetic methods. By combining photoredox and Pd catalysis, a highly efficient, regioselective, and general meta-oxygenation protocol for various arenes has been developed. This protocol operates through a radical pathway and has been demonstrated to work for different substituted arenes using different substituents.