Iodine-catalyzed diazo activation to access radical reactivity

Transition-metal-catalyzed diazo activation is a classical way to generate metal carbene, which are valuable intermediates in synthetic organic chemistry. An alternative iodine-catalyzed diazo activation is disclosed herein under either photo-initiated or thermal-initiated conditions, which represents an approach to enable carbene radical reactivity. This metal-free diazo activation strategy were successfully applied into olefin cyclopropanation and epoxidation, and applying this method to pyrrole synthesis under thermal-initiated conditions further demonstrates the unique reactivity using this method over typical metal-catalyzed conditions. Radical reactivity of diazo compounds, useful organic building blocks, is yet underexplored. Here, the authors report an iodine-catalyzed radical activation of diazo compounds affording a variety of substituted cyclopropanes, pyrroles and epoxides under either thermal- or photo-initiated conditions.