Unexpected Formation of Sterically Congested Oligo(arylene ether)s via Oxidative Coupling of Benzothiophene-Fused Phenols

We attempted to synthesize a sterically hindered bistricyclic aromatic ene based on benzothiophene. Unexpectedly, oxidative coupling yielded highly congested biphenols and oligo(arylene ether)s via C–C and C–O bond formation, respectively. Single-crystal X-ray structural analysis revealed highly twisted, orthogonal structures. The sterically congested oligo(arylene ether)s exhibited high optical transparency in the visible region due to the absence of electronic interactions between the arylene units in the ground state.