Multicomponent Reactions in Open-Air Metal-Free Aqueous Visible-Light Catalysis: Radical–Polar Crossover toward γ-Lactams and γ-Aminobutyric Acids

A green and sustainable synthetic protocol for γ-lactams is developed herein via metal-free three-component photocatalysis using pure water as the sole solvent. This strategy combines the advantages of visible-light activation, one-pot multicomponent coupling, and aqueous-phase synthesis, overcoming the drawbacks of traditional methods such as organic solvent pollution, transition metal residues, and harsh conditions. Employing inexpensive and readily available N-arylglycines, acrylates, and 1,1-diarylethylenes as starting materials, this method enables two consecutive C-C bond-forming events to access a variety of valuable yet otherwise difficult-to-access γ-lactams and γ-aminobutyric acid (GABA) derivatives. Mechanistically, photoredox activation of N-arylglycines generates α-amino radicals upon decarboxylation, which undergo sequential radical addition with acrylic phenol esters and 1,1-diarylethylenes, followed by cyclization to form the pyrrolidinone core. The synthetic utility is further demonstrated by the preparation of δ-amino alcohols and γ-aminobutyric acids together with preliminary asymmetric synthesis studies.