Nickel(0)-Catalyzed [2 + 2 + 2 + 2] Cycloadditions of Terminal Diynes for the Synthesis of Substituted Cyclooctatetraenes

The Ni(0)-catalyzed [2 + 2 + 2 + 2] cycloadditions of 1,6- and 1,7-diynes are shown to provide an efficient and selective method for the preparation of 1,2,5,6-tetrasubstituted cyclooctatetraenes (COTs). Catalysts and conditions are described that favor in all cases COT formation over competing [2 + 2 + 2] cycloadditions. A hitherto unexplored crossed reaction is also described, providing access to non-symmetrical COTs.