Per-Arylation of Pillar[<i>n</i>]arenes: An Effective Tool to Modify the Properties of Macrocycles

Abstract

Installation of various substituents is a reliable and versatile way to alter the properties of macrocyclic molecules, but high-yield and controlled methods are not always available especially for multifold reactions. Herein, we report 10- and 12-fold introduction of aryl substituents onto both rims of cylinder-shaped pillar[<i>n</i>]arenes, which usually have alkoxy substituents slanting to the cylinder axes. Although alkoxy pillar[5]arenes exist as <i>D</i>₅-symmetric enantiomeric pairs, arylated pillar[5]arenes provide crushed single-crystal structures and stereoisomerism including <i>C</i>₂-symmetric conformations depending on the aryl groups. Pillar[<i>n</i>]arenes with 2-benzofuranyl groups display bright fluorescence with quantum yields of 88-90% and no host-guest complexation with electron-deficient molecules in solution due to large deviation from alkoxy compounds. A benzofuran-appended pillar[6]arene instead captures small gaseous molecules in the solid state, probably owing to outside spaces surrounded by aromatic rings.