Nickel‐Catalyzed [2+2+2] Cyclotrimerization of Alkynes and Other Unsaturated Systems: A Literature Overview

Abstract Transition metal‐catalyzed [2+2+2] cyclotrimerization provides easy access to carbocycles and heterocycles in a single operation with complete atom economy. In recent years, nickel catalysis has emerged as a powerful tool for constructing fused arenes and heteroarenes with high regio‐/chemoselectivity and functional group tolerance. This review highlights the historical perspective and advances made in recent years in nickel‐catalyzed [2+2+2] cycloadditions of alkynes, diynes, and various unsaturated systems. The catalytic activity of the nickel complexes, such as Ni‐phosphine, Ni‐NHC, Ni‐pincer, Ni‐diimine, etc, and their mechanistic insights have been thoroughly examined. Highly substituted arenes have broad applications in pharmaceuticals and soft materials. The applications of cyclotrimerization in these areas have been illustrated.