Cobalt-Catalyzed Oxidative Annulation of Nitrogen-Containing Arenes with Alkynes: An Atom-Economical Route to Heterocyclic Quaternary Ammonium Salts.

Four cobalt-catalyzed oxidative annulation reactions of nitrogen-containing arenes with alkynes proceeds by C-H activation, thus leading to biologically useful quaternary ammonium salts, including pyridoisoquinolinium, cinnolinium, isoquinolinium, and quinolizinium salts, in high yields. The results are comparable to those reactions catalyzed by rhodium and ruthenium complexes. The transformation of the salts into various N-heterocycles has also been demonstrated.