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, H-1 NMR, C-13 NMR, and ESI-HRMS.

Automated summary

A metallaphotoredox catalysis protocol has been developed for the efficient dearomatization of indoles using readily available N-quinolyl benzamides under environmentally benign conditions. The reaction allows regioselective functionalization of indoles and provides a mild and economical approach to produce a diverse array of products. Preliminary mechanistic studies suggest a single-electron transfer process is involved, with a catalytically competent organometallic Co(bzac)(3) identified.