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

Abstract

In this paper, a rhodium-catalyzed sequential twofold ortho-CÀ H functionalization of N-phenylbenzimidamide with internal alkyne is reported. The double CÀ H activations proved viable in a one-pot fashion with the assistance of C=N and CÀ 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 CÀ H bonds located on different a moiety of the N-phenylbenzimidamide substrates. Detailed mechanistic studies provided strong support for CÀ H bond cleavage on the N-phenyl ring to be preferential compared with CÀ 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.

Recent Advances in the Synthesis of Isoquinoline-Fused Benzimidazoles

“…The rhodium(III)-catalyzed oxidative annulation of N -(2-phenyl)benzimidamide 17 , which proceeds with use of aryl acetylene 8b at 80 °C, was elaborated by Xu et al (21–81% yield; Figure 14 , top) [ 28 ]. This double C–H activation process proceeds by a one-pot reaction, presumably with C–H bond cleavage occurring preferentially at the N -phenyl ring.…”

“… Structures and CSD reference codes of crystallographically characterized derivatives of benzimidazo[2,1- a ]isoquinolines 1 [ 10 , 11 , 12 , 13 , 20 , 21 , 27 , 28 , 29 , 33 , 34 , 36 , 37 ]. …”

Recent approaches for the synthesis of heterocycles from amidines via a metal catalyzed C–H functionalization reaction

“…The reaction underwent C-H activation/annulation to deliver 2-arylbenzimidazole as key intermediates, which once again undergo C-H functionalization/[4 + 2] annulation, delivering the corresponding benzimidazoisoquinolines derivatives with acceptable yields (Scheme 7). 17 The combination of metal catalysis and electrosynthesis is regarded as a powerful method towards sustainable synthesis, as confirmed by electrochemical metal-catalyzed C-H activation in the past 20 years. Ackermann and co-workers successfully developed a modular electrochemical synthesis of aza-PAHs (nitrogen-doped polycyclic aromatic hydrocarbons) via a rhodium-catalyzed cascade C-H activation/annulation of amidines and alkyne.…”

Open-Air Dual-Diamination of Aromatic Aldehydes: Direct Synthesis of Azolo-Fused 1,3,5-Triazines Facilitated by Ammonium Iodide

“…For instance, Neuville, Huang, Chen, Li, and Cao developed the synthesis of imidazoles by the [3 + 2] annulations of N -arylamidines with C2 synthons such as alkynes, cyclohexanones, sulfoxonium ylides, N -tosyl-hydrazones, nitroolefins, chalcones, cinnamaldehydes, and ynals . Buchwald, Shi, Zhu, and Xu reported the intramolecular annulations of N -arylamidines to give benzimidazoles . Buchwald, Deng, Zhang, Wu, Zhu, Xu, and Hwang described some elegant [5 + 1] annulations of N -arylamidines with aldehydes, DMSO, sulfoxonium ylides, cyclopropenones, isonitriles, or terminal alkynes to obtain quinazolines .…”