Visible Light-Mediated Dearomative Cyclopropanation of Benzoheterocycles via 3- exo -trig Radical Cyclization

Abstract Fused cyclopropanes are prominent motifs in bioactive molecules, yet their incorporation into densely functionalized frameworks remains a significant synthetic challenge. Herein, we report a light-mediated dearomative cyclopropanation of benzoheterocycles enabled by an energy transfer (EnT) cascade. A precisely orchestrated radical sequence selectively generates a homoallylic radical that undergoes a rare 3-exo-trig cyclization, forging a highly strained cyclopropane ring. This transformation converts benzofuran, benzothiophene, and indole derivatives into complex polycyclic architectures bearing cyclopropane-fused units and multiple stereocenters, including contiguous quaternary carbons, with remarkable diastereoselectivity. Mechanistic studies, combining experimental investigations and DFT calculations, support an EnT activation pathway involving neutral diradical intermediates culminating in the unusual 3-exo-trig radical cyclization.