Visible-light-induced catalytic construction of tricyclic aza-arenes from halopyridines

Pyridines and quinolines are prevalent aza-arene motifs existing in drugs and natural products. It is of great interest to develop a more step- and atom-economy strategy for the construction of quinolines from more accessible pyridines. Herein, a visible-light-induced intermolecular cascade cyclization is developed for the coupling of halopyridies with diynes or dienes to construct tricyclic aza-arenes. Mechanistic studies indicate that the reaction processes include pyridyl radical generation, radical cascade addition, and cyclization processes. A series of fused-ring aza-arenes, such as quinoline, isoquinoline, and 5,6,7,8-tetrahydroquinoline, could be obtained via this protocol. Scale-up reaction and further transformations demonstrate the synthetic utility of this approach.