Regioselective [2+2+2] Cycloaddition Reaction Using Allene‐ynes with Simple Allenes under Nickel Catalysis

A Ni‐catalyzed [2+2+2] cycloaddition reaction between allene‐ynes and various mono‐, di‐ and tri‐substituted allenes is described. This protocol effectively differentiates allenyl π components and shows broad substrate generality to give highly functionalized carbocycles. A DFT study played a key role in revealing a detailed reaction mechanism that controls site‐, regio‐ and stereoselectivity, which are thought to originate in the substituent effect on π‐bonds in the early transition state.