Visible-light-induced tandem radical addition–cyclization of 2-aryl phenyl isocyanides catalysed by recyclable covalent organic frameworks

A visible-light-induced tandem radical addition–cyclization sequence via 2-aryl phenyl isocyanides as the starting material and two-dimensional covalent organic frameworks (2D-COFs) as the photocatalyst was developed, delivering multifarious 6-substituted phenanthridines in high yields. Benefitting from the utilization of a heterogeneous photocatalyst, this protocol features easy catalyst separation and excellent recyclability. A negligible loss of the catalytic activity was observed after multiple runs. High practicability of this protocol was further demonstrated by continuous flow experiments.