Photocatalytic Sequential Dimerization and Skeletal Rearrangement of Quinolines: Facile Synthesis of Indole–Methylquinoline Hybrids

Skeletal editing of aromatic heterocycles represents
a promising
strategy for interconverting various aromatic heterocycles, facilitating
rapid alterations in skeletal structures while conserving the essential
features of the original framework. Despite progress in this field,
the ring contraction of quinolines via a radical anion intermediate
continues to pose significant challenges. In this study, we present
a visible-light photocatalytic sequential dimerization and skeletal
rearrangement of quinoline skeletons through reductive activation,
efficiently constructing indole–methylquinoline hybrids. This
reaction showcases a good functional group tolerance, a wide substrate
scope, and mild reaction conditions. A diverse array of quinoline
derivatives, including C2-aryl, C2-carbonyl, and C2-alkyl substituted
quinolines, can participate in this transformation smoothly. Mechanistic
investigations reveal that the single-electron-transfer (SET) reduction
of quinolines to generate quinoline radical anions is a critical step
in this process.