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.