Cobalt(II)-Catalyzed Directed C-H Functionalization/[3+2] Annulation of N -Arylguanidines with Alkynes.

A family of N , N '-diaryl- N ″-(quinolin-8-yl)guanidines were prepared by two methods, and these guanidines were subjected to Co(II)-catalyzed C-H functionalization/annulation with terminal and internal alkynes under mild conditions to afford a family of indole guanidines. Substrates with a range of electronic and steric properties were tolerated. The fluxional behavior of two guanidines and molecular structures of nine compounds are reported. Several key experiments were carried out to support the proposed mechanism of alkyne annulation.