Synthesis and structure of cyclic oligo(p-phenylene oxide)s, -(C6H4O)n- (n = 6-10).

Stepwise growth of oligo(p-phenylene oxide)s and cyclization via the Ullmann coupling reaction by using CuI/N,N-dimethylglycine afforded cyclic oligo(p-phenylene oxide)s, (n = 6-10). The structure of the new cyclophanes was determined by X-ray crystallography, which revealed that they have planar or slightly bent structures with diameters of 1.0-1.5 nm.