Benzylic C-H Esterification with Limiting C-H Substrate Enabled by Photochemical Redox Buffering of the Cu Catalyst

Copper-catalyzed radical-relay reactions provide a versatile strategy for selective C-H functionalization; however, reactions with peroxide-based oxidants often require excess C-H substrate. Here, we report a photochemical strategy to overcome this limitation by using a Cu/2,2 '-biquinoline catalyst that supports benzylic C-H esterification with limiting C-H substrate. Mechanistic studies indicate that blue-light irradiation promotes carboxylate-to-copper charge transfer, reducing resting-state CuII to CuI, which activates the peroxide to generate an alkoxyl radical hydrogen-atom-transfer species. This photochemical redox buffering introduces a unique strategy to sustain the activity of Cu catalysts in radical-relay reactions.

Automated summary

Copper-catalyzed radical-relay reactions offer a versatile strategy for selective C-H functionalization; however, excessive C-H substrates are often needed when using peroxide-based oxidants. In this study, a photochemical approach using a Cu/2,2'-biquinoline catalyst was developed to overcome this limitation and achieve benzylic C-H esterification with limited C-H substrate. Mechanistic studies revealed that blue-light irradiation promotes carboxylate-to-copper charge transfer, leading to the activation of peroxide and generation of alkoxyl radical hydrogen-atom-transfer species. This photochemical redox buffering provides a unique strategy to sustain Cu catalyst activity in radical-relay reactions.