Cobalt-catalyzed radical cyclization of isocyanides forming phenanthridine derivatives

A neutral cobalt(ii) compound Cp*Co(1,2-Ph2PC6H4S) (1, Cp* = Me5C5-) catalyzes the radical cyclization of 2-isocyano-biphenyls with alkyl halides, providing a variety of 6-substituted phenanthridines and phenanthridine-fused polycyclic compounds in good to excellent yields. The mild reaction conditions allow the catalysis to tolerate various alkyl halides for scaled-up syntheses. Polycyclic compounds with a 6-ethylpropanoate group at the C6 position can be hydrolyzed to provide the 6-ethyl substituted N-heterocycles, which exhibit useful emission properties upon protonation.