Construction of N-heterocycles through group 9 (Co, Rh, Ir) metal-catalyzed C-H activation: utilizing alkynes and olefins as coupling partners

ABSTRACT

The building of N-heterocyclic cores endures an influential area of research due to their ubiquitous presence in natural products, agrochemicals, and small bioactive molecules. Over the past two decades, the synthesis of N-heterocycles via C-H activation comes out as a dominating synthetic protocol in atom-economic manner. The creation of C-C/C-N bonds acts as a key determining step for the building of nitrogen-based heterocycles via direct C-H activation protocol, which could serve as a fascinating concept. In recent years, Group 9 (Co, Rh & Ir) transition metal emerged as a robust catalytic system for the development of valuable N-heterocyclic scaffolds among other transition metals due to their mild reaction conditions, high reactivity, and functional group tolerance. A diverse type of arenes such as anilines/anilides, benzamides, hydrazones, ketoximes, benzylamine, and N-aryl nitrones were subjected to the C-H bond activation for the annulation reaction. Moreover, unsaturated compounds such as alkyne and olefin as coupling partners are again the most used companions for the same purpose, i.e., formation of N-heterocycles. Therefore, this review centers on the up-to-date reports on N-heterocycles synthesis by implementing alkynes and olefins as coupling partners through Group 9 transition metals’ catalysis. The methodologies will be based on the coupling of alkynes and olefin, which preferably react in an intermolecular fashion. The scope, limitation, and mechanistic investigation of the Group 9 metal-activated C-H functionalization for the access of N-containing heterocycles with unsaturated reacting partners are the primary focus of the current review.

Graphical Abstract

KEYWORDS:

• N-heterocycles
• group 9 transition metals
• MCp*
• C-H activation
• quinoline
• isoquinoline
• indole
• indoline

Acknowledgment

The authors thank the Director, CSIR-IHBT and communication no. for this manuscript is 4988.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Mr. Shiv Shankar Gupta and Mr. Rohit Kumar acknowledge Council of Scientific & Industrial Research (CSIR), New Delhi, for research fellowship. Ms. Diksha Parmar and Mr. Devesh Chandra thank University Grants Commission (UGC), New Delhi, and Department of Science and Technology (DST), New Delhi for INSPIRE, respectively, for research fellowship. This work is supported by CSIR (MLP0203/MLP0159).