Photocatalytic Radical Transformations of Diazo Compounds: Beyond Carbene

Diazo compounds are versatile building blocks in organic synthesis. Traditionally, their transformations have relied largely on carbene‐mediated pathways. In recent years, however, photocatalytic radical processes have emerged as a powerful alternative, enabling reactions under mild conditions and unlocking distinct reactivity profiles. This review systematically summarizes recent advances in photocatalytic radical reactions of diazo compounds, organized by substrate class. It provides a comprehensive discussion of the reactivity and mechanistic characteristics of representative diazo reagents, including conventional diazo compounds, vinyldiazo compounds, hypervalent iodine diazo reagents, diazo sulfonium species, and alkynyl diazo compounds. Key transformations—such as insertion, cross‐coupling, and cascade cyclization—are highlighted, with particular emphasis on single‐electron‐transfer and proton‐coupled‐electron‐transfer pathways. The review concludes by outlining current challenges and future opportunities in this rapidly developing area.