Carbene–Ketene Formal 3 + 2 Cycloaddition Enabled by Visible-Light-Induced Dual Photolysis of Diazo Compounds

Diazo compounds have long been employed through two distinct reaction pathways: carbene transfer and ketene formation, which rarely intersect within a single reaction environment. Here, we report a visible-light-induced dual photolysis strategy that unifies these divergent pathways by selectively activating two distinct diazo precursors to generate a free carbene and a ketene in situ. The resulting intermediates undergo a formal 3 + 2 cycloaddition, enabling the synthesis of densely substituted furanones bearing quaternary carbon centers. This catalyst-free protocol exhibits a broad substrate scope, operational simplicity, and scalability to gram quantities. Beyond its synthetic utility, representative products display preliminary antifibrotic activity, highlighting the potential of this platform to bridge reactive intermediate chemistry with the development of bioactive scaffolds. This dual photolytic paradigm establishes a conceptual foundation for orchestrating carbene and ketene reactivity within a unified diazo framework.