Visible-Light-Induced Dearomatization via [2+2] Cycloaddition or 1,5-Hydrogen Atom Transfer: Regulating Reaction Pathways of Diradicals on Excited States

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 on excited states are typically involved in this type of reactions as key intermediates. Herein, we report the visible-light-induced divergent dearomatization of indole-tethered O-methyl oximes, in which the reactivity of the open-shelled singlet diradical intermediates towards competitive reaction pathways, namely [2+2] cycloaddition and 1,5-hydrogen atom transfer, can be well regulated. 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 and exclusive selectivity.