Rim-Differentiated C₅-Symmetric Tiara-Pillar[5]arenes

Abstract

The synthesis of “rim-differentiated” C5-symmetric pillar[5]arenes, whose two rims are decorated with different chemical functionalities, has remained a challenging task. This is due to the inherent statistical nature of the cyclization of 1,4-disubstituted alkoxybenzenes with different substituents, which leads to four constitutional isomers with only 1/16th being rim-differentiated. Herein, we report a “preoriented” synthetic protocol based on FeCl3-catalyzed cyclization of asymmetrically substituted 2,5-dialkoxybenzyl alcohols. This yields an unprecedented 55% selectivity of the C5-symmetric tiara-like pillar[5]arene isomer among four constitutional isomers. Based on this new method, a series of functionalizable tiara-pillar[5]arene derivatives with C5-symmetry was successfully synthesized, isolated, and fully characterized in the solid state.

per-Alkoxy-pillar[5]arenes as Electron Donors: Electrochemical Properties of Dimethoxy-Pillar[5]arene and Its Corresponding Rotaxane

“…The scope of pillararenes as hosts can be expanded by substituting the rim alkoxy positions with a desired group; either by cocyclisation of a functionalised monomeric subunit with 1,4-dimethoxybenzene [21,22]; by dealkylation and further reaction of the already formed macrocycle [23][24][25]; or by preorienting the cyclisation reaction with a 2,5-substituted benzyl alcohol [26,27], the latter affording ''rim-differentiated" pillararenes where each rim is pre-functionalised with a desired group. The chemistry of these fascinating molecules has recently been extended to a new family of tiara [5]arenes that exhibit more conformational flexibility [28].…”

Tiara[5]arenes: Synthesis, Solid‐State Conformational Studies, Host–Guest Properties, and Application as Nonporous Adaptive Crystals

“…Thekey step in the synthesis of tiara [5]arenes is the initial formation of the RD-P [5] precursor.I nstead of ah eads-ortails statistical cyclization characterized by very low yields, our synthesis started with amonomer that aligns in ahead-totail manner,r esulting in ah ighly selective synthesis of RD-P [5]s,that is,55%selectivity among all four P [5] consitutional isomers and 20 %y ields of isolated product. [14] In the beginning we set out to improve the yield of the RD-P [5] synthesis,w idening ab ottleneck in our synthesis.O ne major limitation to be overcome in the oligocyclization is the retro-Friedel-Crafts reaction;after formation of the arylÀCH 2 Àaryl moiety,t he reaction can reverse. [19] Ther esult is the generation of the other three undesired P [5] isomers,rather than an exclusive synthesis of RD-P [5] that would have occurred had this retro Friedel-Crafts reaction not occurred (see the Supporting Information).…”

“…[12] Pillararenes,n amed after their characteristic cylindrical pillarshaped cavities,h ave gained considerable popularity in the past decade on account of their facile syntheses,v ersatility towards derivatization, and rich host-guest chemistry.T he synthesis of the pentameric homologue,p illar [5]arene [13] (P [5]), is especially high-yielding,a llowing the construction of aw ide range of supramolecular architectures based on symmetric P [5]s with identical functionalities on both rims. Furthermore,recent developments from our group and others have opened up rim-specific functionalizations,leading to the so-called rim-differentiated [14][15][16] P [5]s (RD-P [5]s) with different top and bottom rims (R 1 ¼ 6 R 2 ;F igure 1) to be prepared and further functionalized in atailor-made fashion.…”

Structural Diversification of Pillar[n]arene Macrocycles

“…Alternatively, different alkoxy substituents have been introduced by using asymmetrically modified dialkoxybenzene precursors for the PA[ n ] synthesis, leading to rim‐differentiated PA[ n ]s (RD‐PA[ n ]s), also referred to as tiara[ n ]arenes (Scheme b) . A final route towards mono‐ and bifunctional PA[ n ]s has been developed based on statistical co‐condensation of two different dialkoxybenzenes, providing straightforward access to PA[ n ]s having different alkoxy substituents on different rings (Scheme c) . Even though these methods provide synthetic handles for making functionalized PA[ n ]s, they remain limited to macrocyclic structures that have two alkoxy substituents on all benzene rings.…”