1,2,3,4-Tetraethynylbenzene as a Template for Cobalt-Catalyzed Alkyne Cocyclizations: Synthesis of 2,3,8,9-Tetrakis(trimethylsilyl) Angular [3]Phenylene and Bent [5]Phenylene (Benzo[1′′,2′′:3,4;3′′,4′′:3′,4′]dicyclobuta[1,2-<i>b</i>:1′,2′-<i>b</i>′]bisbiphenylene)
An approach to the synthesis of bent phenylenes is described, which features 1,2,3,4-tetraethynylbenzene as starting material. Application of this synthon in CpCo-catalyzed alkyne cocyclizations allows the total synthesis of bent [5]phenylene, the seventh isomer of the family of twelve [5]phenylenes to be isolated.