Facile Intramolecular Cyclization in Oxidative Coupling of Acetylenes Linked to 1,3-Positions of Benzene:  Strained [12]Metacyclophanedienetetrayne System

Oxidative coupling of ethynylpropellane linked to 1,3,5-position of a benzene core 3b did not give the cage dimer 2 but the dimer 4 having a strained [12]metacyclophanedienetetrayne system. The spectral and structural features of the novel ring system were revealed for the simple dibenzo derivative 6, which was also prepared efficiently by the intramolecular cyclization of the open-chain precursor.