Integrating\nUmpolung and CO<sub>2</sub> Shuttling\nStrategies for the Synthesis of <sup>1</sup><sup>2</sup>C- and <sup>13</sup>C‑α-Ketoacids from Aldehydes

The direct carboxylation of aldehydes with CO<sub>2</sub> is rare\ndue to the polarity mismatch between these two electrophilic substrates.\nTo address this challenge, we propose a sequential approach for synthesizing\nα-ketoacids from commercially available aldehydes by integrating\numpolung and CO<sub>2</sub> shuttling strategies. This transition\nmetal-free shuttle carboxylation method enables the transfer of CO<sub>2</sub> from triphenylacetic acid potassium salt to thioacetal, eliminating\nthe need for handling pressurized CO<sub>2</sub> gas or using specialized\nequipment, while also enhancing the reaction’s functional group\ntolerance. Furthermore, the use of stoichiometric or slightly excess\namounts of triphenylacetic acid potassium salt as a formal CO<sub>2</sub> donor makes it suitable for complete <sup>1</sup><sup>3</sup>C labeling of α-ketoacids.