Symmetrically Tetra-functionalized Pillar[6]arenes Prepared by Fragment Coupling

Due to the highly symmetrical structures generated from one-pot syntheses, the partial functionalization of macrocycles is usually beset with low yields and onerous purifications of the target multifunctional macrocycles. To improve this situation, taking pillar[6]arenes as an example, a two-step fragment coupling method has been developed for synthesizing symmetrically tetra-functionalized pillar[6]arenes, namely X-pillar[6]arenes. This method is simple and versatile, which makes hetero-fragment coupling and pre-functionalization available. Nine new macrocycles and a pillar[6]arene-based cage have been prepared. In addition, one of the newly synthesized macrocycles, COOEtEtXP[6], exhibits a strong cyan luminescence in the solid state under irradiation by 365 nm UV light. This emission originates from intramolecular through-space conjugation. Meanwhile, formation of a supramolecular polymer by multiple non-covalent intra/intermolecular interactions helps rigidify the structure and make COOEtEtXP[6] an efficient solid-state emitter. It is believed that this fragment coupling can also be used to realize the multi-functionalization of other macrocycles.

Automated summary

Due to the highly symmetrical structures, partial functionalization of macrocycles is usually low-yielding and difficult to purify. In this study, a two-step fragment coupling method was developed to synthesize tetra-functionalized pillar[6]arenes, referred to as X-pillar[6]arenes. This method is simple and versatile and allows for hetero-fragment coupling and pre-functionalization.