Photoinduced transition metal-catalyzed cyclization for heterocycle synthesis

Visible light-driven transition metal catalysis enables efficient synthesis of diverse heterocycles under mild conditions. This review systematically summarizes two key strategies, including dual catalytic systems employing external photocatalysts with metals, and direct visible light-driven metal-catalyzed cyclizations. Key mechanisms, including ligand-to-metal charge transfer, along with single-electron transfer and energy transfer, are examined for their roles in enabling radical-involved cyclizations, C H functionalization, and asymmetric transformations. Moreover, this review centers on analyzing how ligand design and modulation of the metal coordination sphere govern these photophysical processes, stabilize key intermediates, and ultimately control reaction pathways and selectivity. The broad scope of accessible heterocyclic architectures is presented, alongside a discussion of future challenges centered on developing earth-abundant metal catalysts, mechanistic understanding, and scalable processes.