Synthesis of Functionalized Cyclopropanes from Carboxylic Acids by a Radical Addition–Polar Cyclization Cascade

Herein, we describe the development of a photoredox‐catalyzed decarboxylative radical addition–polar cyclization cascade approach to functionalized cyclopropanes. Reductive termination of radical–polar crossover reactions between aliphatic carboxylic acids and electron‐deficient alkenes yielded carbanion intermediates that were intercepted in intramolecular alkylations with alkyl chlorides appended to the alkene substrate. The mild conditions, which make use of a readily available organic photocatalyst and visible light, were demonstrated to be amenable to a broad range of structurally complex carboxylic acids and a wide variety of chloroalkyl alkenes, demonstrating exquisite functional group tolerance. The development of a fragment coupling‐based cyclopropanation between carboxylic acids and chloroalkyl alkenes is described. The reaction involves a photoredox‐catalyzed decarboxylative radical addition–polar cyclization cascade and uses a readily available organic photocatalyst. The mild conditions provide access to diversely functionalized cyclopropanes from a broad range of structurally complex carboxylic acid and alkene substrates.