Syntheses of syn and anti doublebent [5]phenylene.

[structure: see text] The parent and dipropyl-substituted anti (1a,b) and syn doublebent (2a,b) [5]phenylenes have been assembled by CpCo-catalyzed double cyclization of regiospecifically constructed appropriate hexaynes. (1)H NMR, NICS, and an X-ray structural analysis of 1a reflect the aromatizing effect of double angular fusion on the central ring of the linear [3]phenylene substructure.

Synthesis of bent [4]phenylene (cyclobuta[1,2-a:3,4-b']bisbiphenylene) and structure of a bis(trimethylsilyl) derivative: the last [4]phenylene isomer.

The syntheses of the title compounds were accomplished by cobalt-catalyzed alkyne cyclotrimerizations using two strategies; the properties of the bent phenylene frame reflect the combined effects of benzocyclobutadienofusion of the component [3]phenylene substructures.