Visible-Light Photoredox-Catalyzed Carboxylation of Benzylic C(sp3)-O Bonds in Ethers with CO2

Abstract

Although significant progress has been made in achieving site-selective C-O bond functionalization in specific substrates, the selective cleavage and functionalization of C(sp³)-O bonds in ethers remain a fundamental challenge in synthetic chemistry. Herein, we present an efficient carboxylation method via the photoredox-catalyzed cleavage of benzylic C(sp³)-O bonds in ethers with carbon dioxide (CO₂). Diverse primary, secondary, and tertiary benzyl ethers undergo selective carboxylation with CO₂ to generate valuable aryl acetic acids, including several drug molecules. This photocatalyzed carboxylation reaction is operationally simple to implement and versatile for various benzylic ethers, exhibiting favorable compatibility with diverse functional groups. Mechanistic studies indicate that the single electron transfer (SET) reduction of ethers might be the key to generating a highly reactive radical anion intermediate, which could undergo C-O bond cleavage and another SET reduction process to generate carbanions for reaction with CO₂.