Boryl Radical Activation of Benzylic C-OH Bond: Cross-Electrophile Coupling of Free Alcohols and CO2 via Photoredox Catalysis

A new strategy for the direct cleavage of theC(sp3)-OH bond has been developed via activation of freealcohols with neutral diphenyl boryl radical generated from sodiumtetraphenylborate under mild visible light photoredox conditions.This strategy has been verified by cross-electrophile coupling offree alcohols and carbon dioxide for the synthesis of carboxylicacids. Direct transformation of a range of primary, secondary, and tertiary benzyl alcohols to acids has been achieved. Controlexperiments and computational studies indicate that activation of alcohols with neutral boryl radical undergoes homolysis of theC(sp3)-OH bond, generating alkyl radicals. After reducing the alkyl radical into carbon anion under photoredox conditions, thefollowing carboxylation with CO2affords the coupling product

Automated summary

A new strategy for direct cleavage of the C(sp3)-OH bond has been developed using neutral diphenyl boryl radical to activate free alcohols. Under mild visible light photoredox conditions, this strategy has been verified by cross-electrophile coupling of free alcohols and carbon dioxide to synthesize carboxylic acids. Control experiments and computational studies have shown that the activation of alcohols with neutral boryl radical leads to homolysis of the C(sp3)-OH bond, generating alkyl radicals, which can be further transformed into carbon anions for carboxylation with CO2 to form the coupling product.