ABSTRACT Macrocyclic hosts are at the core of artificial molecular recognition and supramolecular assemblies. The key to successful hosts is easy synthesis/functionalization, 3D structures with suitable cavities, and characteristic surfaces inside/outside the macrocycles. While big successes have been limited to a few host families, recent progress in derivatization has enabled a macrocyclic family, pillar n arenes, to exhibit drastically modified 3D structures and properties. These results expand the chemistry of pillar n arene into that of more general 2,5‐disubstituted 1 n paracyclophanes. This review overviews such unconventional pillar n arenes focusing on the 3D structures, which are one of the aforementioned keys to a big success. Various stereoisomerism and conformations of the “broad‐sense” pillar n arenes are discussed using average torsion angles as description values for continuously inclining π‐panels. This makes a sharp contrast to conventional pillar n arene chemistry that has limited structural description to an interconvertible pair of discrete ( R p / S p ) conformations.
Kato et al. (2026) studied this question.