Rhodium(III)-Catalyzed Oxidative Annulation of Amidines with Alkynes via Sequential C-H Bond Activation

In this paper, a rhodium-catalyzed sequential two-fold ortho-C-H functionalization of N-phenylbenzimidamide with internal alkyne is reported. The double C-H activations proved viable in a one-pot fashion with the assistance of C=N and C-N bonds, providing a series of benzimidazoisoquinolines with high levels of positional selectivity control. The operationally simple transformation showed high functional group compatibility and featured the cleavage of C-H bonds located on different a moiety of the N-phenylbenzimidamide substrates. Detailed mechanistic studies provided strong support for C-H bond cleavage on the N-phenyl ring to be preferential compared with C-H bond cleavage on C-phenyl ring. As a multifunctional catalytic platform, the rhodium catalyst conducted two independent and compatible catalytic cycles in one pot.