VISIBLE-LIGHT-MEDIATED DEAROMATIVE CYCLOPROPANATION OF BENZO-HETEROCYCLES VIA ENERGY-TRANSFER

otherwise unreactive organic molecules.1 Herein, we disclose the first energy-transfer-mediated dearomative cyclopropanation of benzo-heterocycles, providing an atom-economical strategy for the rapid construction of highly strained cyclopropane-fused polycyclic architectures.2,3 Such scaffolds represent privileged structural motifs found in natural products and bioactive molecules, as Lundurine B, Brimarafenib, and Lifirafenib.4 Mechanistic investigations support an EnT activation pathway involving neutral diradical intermediates and a radical cascade culminating in an intramolecular 3-exo-trig cyclization that generates an α-cyclopropyl radical which, contrary to its typical propensity for ring opening, undergoes cyclization to form the cyclopropane ring. This unusual radical reactivity pattern enables a radical cascade that rapidly assembles complex three-dimensional frameworks from simple benzo-heterocyclic precursors.5 Notably, four new C–C bonds and up to six stereocenters are formed, including contiguous quaternary carbon centres, with good to excellent diastereoselectivity. The transformation efficiently converts benzofurans, benzothiophenes, and indoles into 22 previously unreported cyclopropane-fused products, generating exceptional molecular complexity in a single synthetic step