Light-Driven Organocatalytic Birch Reduction for Late-Stage Drug Modification and sp3-Rich Spirocycle Synthesis

The Birch reduction is a cornerstone transformation in synthetic chemistry, yet its widespread application is limited by harsh conditions, poor functional group tolerance, and safety concerns. Recent photochemical strategies have offered milder alternatives but have largely been restricted to polycyclic arenes (E-red similar to -2.6 V vs SCE) and poorly suited for complex molecules of pharmaceutical relevance. Here, we report a practical organocatalytic system that enables Birch-type reductions of electron-rich benzenes (E-red = <-3.4 V vs SCE) and heteroarenes under light irradiation and mild conditions. The method is based on an indoline-2-thione anion catalyst developed from our previously reported organic super-reducing photocatalysts. The protocol exhibits a broad substrate scope, including the late-stage functionalization of drug molecules bearing sensitive functional groups. Moreover, the synthetic utility of 1,4-dihydro products bearing an alcohol side chain was showcased through a two-step telescoped Birch reduction/spirocyclization sequence, granting streamlined access to sp(3)-rich spirocyclic scaffolds, a valuable motif in medicinal chemistry. Demonstrated scalability in both batch and continuous-flow operation further underscores the translational potential of this system. This collaborative work with colleagues at Johnson & Johnson highlights the power of light-driven organocatalysis to deliver industrially relevant methods for the synthesis of complex drug-like molecules.