Synergistic Photoredox/Palladium Catalysis Enables Enantioconvergent Cross-Electrophile Esterification with CO2

Herein, we presented a synergistic catalytic system that utilizes 4CzIPN and (R)-L1/Pd(acac)2 as catalysts for an efficient and enantioconvergent synthesis of axially chiral esters from racemic heterobiaryl bromides and alkyl bromides with CO2 under mild conditions. A wide range of axially chiral esters, featuring various functional groups, were obtained through this novel methodology in good to high yields with excellent enantioselectivities. Detailed mechanistic studies unveiled that the ratio of 4CzIPN/[Pd/(R)-L1] significantly influences the chemo- and enantioselectivity of the reaction. Kinetic studies and control experiments supported the proposed mechanism involving cascade asymmetric carboxylation followed by SN2 substitution. Achieving high enantioselectivities relies not only on the choice of synergistic metallaphotoredox catalysts but also on the utilization of alkyl bromides, which trap the generated chiral carboxylic anions in situ, preventing their immediate racemization.