Pillararenes are macrocyclic compounds consisting of hydroquinone units connected by methylene groups. In 2008, Ogoshi et al. reported the first synthesis of 1,4-dimethoxypillar[5]arene (= DMpillar[5]arene).1) DMpillar[5]arene is a ring-shaped molecule that, unlike calixarene with its basket-shaped structure, has a highly symmetrical columnar three-dimensional structure. Research is underway on the application of pillararenes in host-guest chemistry and in the development of supramolecular materials, such as rotaxanes.