Metallaphotoredox Dearomatization of Indoles by a Benzamide-Empowered [4 + 2] Annulation: Facile Access to Indolo[2,3-c]isoquinolin-5-ones

Herein, we report a metallaphotoredox catalysis protocol enabling the efficient dearomatization of indoles utilizing readily available N-quinolyl benzamides under environmentally benign reaction conditions. This reaction allows regioselective C–2 and C–3 dual functionalization of indoles and provides a mild, straightforward, and high atom- and step-economical approach to produce a diverse array of indolo[2,3-c]isoquinolin-5-ones by merging cobalt catalysis with photocatalysis. The practicality and effectiveness of this synergistic protocol were illustrated by a gram-scale experiment. Preliminary mechanistic studies indicate that a single-electron transfer process is involved during the catalytic cycle. In addition, a catalytically competent organometallic Co(bzac)3 has been identified through X-ray crystallography, 1H NMR, 13C NMR, and ESI-HRMS.