Diazo compounds: beyond carbenes as radical precursors in light-driven organic transformations

Diazo compounds are traditionally known as privileged carbene precursors. However, recent advances in photochemistry have revealed a distinct reactivity paradigm: their activation as radical precursors under visible-light irradiation. Pioneering studies by Gryko and Doyle established complementary strategies-cobalt-catalysed radical generation and proton-coupled electron transfer (PCET)-that have since inspired a surge in methodologies exploiting diazo compounds in radical transformations. This highlight reviews the key developments, mechanistic insights, and emerging strategies that define this rapidly evolving area. By unifying diverse approaches, we aim to provide a cohesive perspective on the state-of-the-art and outline future opportunities for diazo-based radical chemistry under photochemical conditions.