Nickel-catalyzed highly chemoselective cocyclotrimerization of arynes with allenes: a novel method for 10-methylene-9,10-dihydrophenanthrenes.

The NiBr(2)(dppe)-Zn system effectively catalyzes the [2+2+2] cocyclotrimerization of arynes with allenes, leading to 10-methylene-9,10-dihydrophenanthrenes in moderate to good yields. The cocyclotrimerization is highly selective with only the internal double bond of the allenes being involved in the reaction.