Light-Driven Epimerization: Diastereoconvergent Synthesis of [¹²C, ¹³C] β^2,3-Amino Acids

β-Amino acids are crucial building blocks for bioactive peptides and pharmaceuticals, wherein the stereochemistry of C², C³-disubstituted β^2,3-amino acids dictates the secondary structure of β-peptides. However, the diastereoselective synthesis of these scaffolds remains a formidable challenge. Herein, we report a novel photocatalytic cascade enabling the one-pot hydrogenation, carboxylation, and epimerization of α,β-unsaturated imines. This method provides direct and highly diastereoselective (d.r. up to 35:1) access to valuable syn-β^2,3-amino acids. Time-course analysis and DFT calculations reveal a unique light-driven dynamic kinetic epimerization process that ensures stereoconvergence to the thermodynamically favored syn-isomer. Notably, this strategy also facilitates the facile synthesis of ¹³C-labeled syn-β^2,3-amino acids using commercially available ¹³C-sodium formate, achieving exceptional isotope incorporation (93%-98%) that surpasses existing ¹³CO₂-based methods. Furthermore, the system's utility is demonstrated through the gram-scale synthesis of N-unprotected α-amino acids from imines (11 g, 75% yield), more significantly, via a one-pot procedure directly from diaryl ketones.