Photoredox Asymmetric Nucleophilic Dearomatization of Indoles with Neutral Radicals

The
dearomatization of indoles represents the most efficient approach
for accessing highly valued indolines. The inherent nucleophilic reactivity
of indoles has dictated indole dearomatization development in both
1e– and 2e– processes. However,
the dearomatization of electron-deficient indoles has been challenging.
Herein, we introduce a conceptually distinct photoredox-mediated Giese-type
transformation strategy, which is generally used for the conjugate
addition of radicals to simple α, β-unsaturated systems,
for chemoselectively breaking CC bonds embedded in the aromatic
structure. Moreover, highly diastereoselective addition of challenging
neutral radicals has been achieved by Oppolzer camphorsultam chiral
auxiliary. Structurally diverse amine-functionalized chiral indolines
carrying distinct functional and stereochemical diversity are produced
from a wide array of amines as radical precursors. Furthermore, the
mild, powerful manifold is capable of the late-stage modification
of complex natural products and pharmaceuticals. DFT studies are performed
to elucidate the observed stereochemical outcomes.