Visible-Light-Induced Dearomatization via [2+2] Cycloaddition or 1,5-Hydrogen Atom Transfer: Divergent Reaction Pathways of Transient Diradicals

Visible-light-induced dearomatization reaction via energy-transfer mechanism is an emerging strategy for the synthesis of highly strained polycyclic molecules. Transient, high-energy diradical species are typically involved in this type of reaction as key intermediates. Herein, we report the visible-light-induced divergent dearomatization of indole-tethered O-methyl oximes, in which the reactions of the open-shelled singlet diradical intermediates toward competitive [2 + 2] cycloaddition or 1,5-hydrogen atom transfer can be achieved with exclusive selectivity. The mechanism has been well supported by a series of experimental and computational investigations. The dearomatization reactions allow the facile synthesis of structurally appealing indoline-fused azetidines and related polycyclic molecules with high efficiency.