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.