Combining Umpolung and Carbon Isotope Exchange Strategies for Accessing Isotopically Labeled α‑Keto Acids

The integration of umpolung and carbon isotope exchange for accessing isotopically labeled α-keto acids through photoredox catalysis is elucidated. This process involves the carbonyl umpolung of C­(sp2)-α-keto acids to yield C­(sp3)-α-thioketal acids, followed by the carbon isotope exchange of C­(sp3)-α-thioketal acids, and ultimately, deprotection to generate carbon-labeled α-keto acids.