Bromide-promoted cascade annulation of isocyanobiaryls with aldehydes through photoredox catalysis

Herein, we report a cascade annulation of readily available isocyanobiaryls with simple aldehydes via photoredox catalysis, providing a straightforward approach towards valuable 6-hydroxyalkylated phenanthridines. Mechanistic studies indicated the generation of a key acyl radical from aldehydes by hydrogen atom abstraction with a bromine radical. This protocol exhibits exceptional chemoselectivity, excellent tolerance of various functional groups and mild reaction conditions. Its synthetic utility was demonstrated by a gram-scale reaction and various facile manipulations of the free hydroxyl group to furnish diverse phenanthridine derivatives.