Copper-Mediated Radical Cyclopropanation of Activated Alkenes under Continuous-Flow Conditions.

Polysubstituted cyclopropanes are valuable in complex molecule synthesis but challenging to access due to low atom economy and harsh conditions. Herein, we report a copper-mediated, peroxide-initiated cyclopropanation of activated alkenes with active methylene compounds via a radical pathway. This diazo-free, prefunctionalization-free method, integrated with continuous flow, enhances safety, scalability, and efficiency. Operable under mild conditions with broad substrate scope, it offers a practical and atom-economical route to diverse polysubstituted cyclopropanes.