Per-Arylation of Pillar[n]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[n]arenes, which usually have alkoxy substituents slanting to the cylinder axes. Although alkoxy pillar[5]arenes exist as D 5-symmetric enantiomeric pairs, arylated pillar[5]arenes provide crushed single-crystal structures and stereoisomerism including C 2-symmetric conformations depending on the aryl groups. Pillar[n]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.

Functionalization of pillar[n]arenes towards optically responsive systems via host–guest interactions

“…Chen and coworkers first reported the pillar[5]arene-based CPL materials, 129 which triggered the exploration of various types of pillar[5]arene-based CPL materials. 107,130–136 These materials are usually prepared by introducing bulky conjugated moieties to simultaneously fix the planar chirality and provide luminescence in the visible light region. However, host–guest complexation does not produce a dramatic CPL response because the fixed planar chiral pillar[ n ]arenes do not exhibit large conformational changes in response to guest addition.…”

Alignment and Dynamic Inversion of Planar Chirality in Pillar[n]arenes

“…They also achieved per‐arylation on both pillar[5,6]arene rims using less bulky furan and benzofuran rings ( 5 a – c ) [38] . Besides largely deviated structural and host–guest characteristics, 5 a gave three sets of enantiomers as isolable species, which is in sharp contrast to alkoxy pillar[ n ]arenes.…”

“…2 b [b,34] n-hexane 403 0.7 0.72 15.9 (303) 2 c [34] n-hexane 422 6.1 0.33 60.5 (305) 3OMe [c,29] MeCN 333 5.1 0.11 23 (240) 3CO 2 Et [29] MeCN 402 0.4 0.77 14 (230) 5 a [38] CHCl 3 424 0.4 0.88 25 (320) 10 c [41] CHCl 3 547 7.0 0.01 4 (288)…”

Stereoselective Single Step Cyclization to Give Belt-Functionalized Pillar[6]arenes

“…Numerous pillar­[ n ]­arenes have been reported containing a vast array of chemical functionalities; however, the overwhelming majority of variation in pillar­[ n ]­arene structures have involved the rim groups (i.e., the OR groups in Figure ). – Typically, substituents are either preinstalled at these positions and retained during cyclization or a per-methoxy or per-ethoxy pillar­[ n ]­arene is synthesized, and then one or more alkyl group is removed allowing for subsequent functionalization. ,– This rim functionalization approach has two advantages: it is typically synthetically straightforward, and it also typically does not impact the pillar-like geometry of the macrocycle.…”