A straightforward route to substituted 1-pyrrolines via photocatalyzed ring-opening cyclization of cyclopropyl enamines

Here we introduce a practical and efficient two-step protocol for the synthesis of structurally diverse 1-pyrroline derivatives starting from readily available cyclopropylamines and β-keto derivatives. The key transformation is a ring-opening radical cyclization enabled by visible-light mediated photoredox catalysis, which proceeds under mild conditions through a redox-neutral and atom-economical pathway. This new disconnection allows the formation of challenging structures, such as spirocyclic pyrrolines and shows excellent functional group tolerance also enabling the late-stage diversification of pharmaceutically relevant molecules. This transformation is compatible with a continuous flow approach, extensible to a telescoped setup that integrates both steps and enables scalable synthesis. As application, a fed-batch reduction was implemented, furnishing 1-pyrrolidine frameworks relevant to bioactive scaffolds, such as indolizidine alkaloid precursors. This streamlined strategy provides a general, catalytic, and highly efficient method utilizing readily available precursors for a sustainable and modular approach to nitrogen-containing heterocycles.