Figure 1. Design plan for α-carboxylation of amines with CO₂.

a, Carbon–carbon bond formation with CO₂ has generally relied on two-electron reaction pathways with an extended π system or a strong nucleophile. cat., catalyst. b, Single-electron reduction of carbon dioxide and its reaction with an α-amino radical to provide α-amino acid. c, Continuous flow setup for the photoredox-catalyzed synthesis of α-amino acids. The reactants were introduced via a gas-tight syringe containing a solution of the amine substrate, base, and catalyst. CO₂ gas was metered into the system by a MFC. These two streams were joined by a T-mixer before irradiation under a UV lamp. The pressure of CO₂ is controlled by a BPR. MFC, mass flow controller; BPR, back pressure regulator.