Alkynes occupy a prominent role as coupling partner in the transition metal-catalysed directed C-H activation reactions. Due to low steric requirement and linear geometry, alkynes can effectively coordinate with metal...

Transition metal-catalyzed C-H activation and functionalization with various coupling partners is a well-explored area of research. Among the various coupling partners used, alkynes occupy a prominent position on account of their varied reactivity. Due to their low steric demand and a high degree of unsaturation they effectively overlap with metal d-orbitals and form multiple bond-forming events giving rise to complex skeletons that are otherwise challenging to synthesize. This makes alkyne one of the most successful coupling partners in terms of the number of useful transformations. Remarkably, by changing the reaction conditions and transition-metals from 5d to 3d, the behaviors of alkynes also change. Despite enormous explorations with alkynes, there are still a lot more possible ways by which alkynes can be made to react with M-C bonds generated through C-H activation. Especially with the development of new high and low valent first-row metal catalysts, there is plenty of scope for this chemistry to evolve as one of the most explored areas of research in coming years. Therefore, a review on this topic is both timely and useful for synthetic chemists who are working in this area. In this review, we have highlighted the diverse reactivity of alkynes with various transition metals and their applications along with some of our thoughts on future prospects.

Herein, we report the reactivity of cobalt(III)-catalyst towards hydroarylative functionalization of 1,6-diyne, which has never been explored before. The N-aryl lactam is the prime substrate that undergoes sp 2 CÀ H bond activation. CÀ Co(III) bond formation occurs through weakly coordinating lactam group. The reaction mechanism reveals the in-situ formation of a six-membered cobaltacycle which undergoes further functionalization with 1,6-diyne. Also, radical quenching experiments suggest the involvement of the ionic pathway for this conversion. In addition, hydrogen scrambling and kinetic isotope experiments support the proposed mechanism. A wide range of electronically biased substrates and reacting partners work well with this method in a highly atom-economical fashion.