Combined Bronsted Base-Promoted CO2 Fixation into Benzylic C-H Bonds of Alkylarenes

Interest in developing methods for direct CO2 fixation into readily available unfunctionalized C-H bonds in organic substances has recently surged. In contrast to the well-studied carboxylations of alkynyl C(sp)-H and aromatic C(sp(2))-H bonds, carboxylation of benzylic C(sp(3))-H bonds to produce 2-arylacetic acids is limited to photoirradiation reactions and continues to be a challenging issue because of the low chemical reactivity. We herein describe that a combined Bronsted base (i.e., LiO-t-Bu/CsF and LiOCEt3/CsF) achieves benzylic carboxylation of electron-deficient, -neutral, and -rich alkylarenes and enables various functionalities, including fragile ones such as bromide, alkene, alkyne, and carbonyl moieties. Dicarboxylation at the benzylic position is also established. Cs-alkoxide generated in situ acts as a reactive base, as demonstrated in experiments with independently prepared CsO-t-Bu and by Cs-133 nuclear magnetic resonance studies.

Automated summary

Interest in developing methods for direct CO2 fixation into readily available unfunctionalized C-H bonds in organic substances has recently surged. In this study, a combined Bronsted base was used to achieve the carboxylation of benzylic C-H bonds, resulting in the formation of various functional moieties.