Diazo-Preserving Radical Cascades for the Modular Photoinduced Synthesis of Oxindoles and Pyrazolones

We report a metal-free photocatalytic strategy for the modular synthesis of diazo-containing oxindoles and pyrazolones from readily available precursors. Diazomethyl radicals are generated either via a three-component electron donor-acceptor (EDA) complex involving acrylamides or through a photoredox cycle for the activation of hydrazides, enabling C(sp²)-C(sp³) bond formation while preserving the diazo functionality. The method tolerates a broad range of functional groups, substitution patterns, and pharmaceutically relevant motifs. Mechanistic studies, including radical trapping, UV-vis spectroscopy, light on/off experiments, and Stern-Volmer analysis, support a radical chain propagation and distinguish the EDA-driven versus photoredox pathways. The resulting diazo heterocycles undergo downstream transformations to access new chiral centers and functional motifs.