Regioselective Synthesis of Methylene-Bridged Naphthalene Oligomers and Their Host-Guest Chemistry

Recent advances in the synthesis and applications of macrocyclic arenes

Macrocyclic arenes including calixarenes, resorcinarenes, cyclotriveratrylene, pillararenes and so on have emerged as highly attractive synthetic macrocyclic hosts due to their unique structures, facile functionalization, and broad range of applications. In recent years, there has been growing interest in the development of novel macrocyclic arenes composed of various aromatic building blocks bridged by methylene groups, which have found applications in various research areas. Consequently, the development of novel macrocyclic arenes has become a frontier and hot topic in supramolecular and macrocyclic chemistry. In this review, we feature the recent advances in the synthesis and applications of novel macrocyclic arenes that have emerged in the last decade. The general synthetic strategies employed for these macrocyclic arenes are systematically summarized, and their wide applications in molecular recognition and assemblies, molecular machines, biomedical science and functional materials are highlighted.

Prismarene: An Emerging Naphthol-Based Macrocyclic Arene

Phenol-based macrocyclic arenes have been widely used in supramolecular chemistry, significantly enriching the toolbox of the field. In contrast, naphthol-based macrocyclic arenes are rather underdeveloped. Very recently, Gaeta and co-workers successfully synthesized such macrocycles (referred to as prism[n]arenes) with good guest-binding ability by reacting 2,6-dimethoxynaphthalene with paraformaldehyde under optimized conditions. In view of the simple synthesis and good host-guest chemistry, we anticipate that this macrocycle will find similar success and wide applications as the phenol-based macrocyclic arenes.

Prismarenes: A New Class of Macrocyclic Hosts Obtained by Templation in a Thermodynamically Controlled Synthesis

The novel title macrocycles, based on methylene-bridged 1,5-naphthalene units, have been obtained by template effect in a thermodynamically controlled synthesis. In detail, the prism[5]arene 1 or the prism[6]arene 3 was selectively removed from the equilibrium mixture by using the complementary ammonium-templating agent. When only the solvent 1,2-DCE was used, the 1,4-confused derivative 2 was obtained. The prism[5]arene here described shows a deep π-electron-rich aromatic cavity that exhibits a great affinity for the quaternary ammonium guests, originating from favorable cation···π and ⁺NC–H···π interactions. This recognition motif is the basis of the templated synthesis of the prism[n]arenes here reported.

Synthesis and Host-Guest Properties of Acyclic Pillar[n]naphthalenes

Here we report a new class of synthetic receptors, acyclic pillar[n]naphthalene (n = 2–4, Dimer, Trimer, and Tetramer) oligomers, which are made up of 2,3-diethoxynaphthalene units linked by methylene bridges at the 1- and 4-positions. They can be synthesized through a one-step condensation of 2,3-diethoxynaphthalene monomer and paraformaldehyde in the presence of BF₃•(Et)₂O catalyst. The crystal structure of Tetramer has an interesting pseudo-cycle shaped structure in the solid state. Their complexation behaviors toward several organic ammonium cations (1⁺-15⁺) and electron–deficient neutral guests (16–17), were examined by means of ¹H NMR spectroscopy. Tetramer shows good host-guest properties toward the ammonium guests, giving association constants (K_a) in the magnitude of 10²-10⁴ M⁻¹, which are comparable with those for some macrocyclic hosts.

Syntheses of water-soluble acyclic naphthalene oligomers and their applications in water

Water-soluble -CH2- bridged acyclic naphthalene oligomers (WN2 and WN3) were designed and prepared successfully. Interestingly, WN3 can be used in reversible dispersion of carbon nanotubes in water by changing the pH efficiently.

Unexpected solvent effect on the binding of positively-charged macrocycles to neutral aromatic hydrocarbons

A pair of positively charged naphthotubes was synthesized by using imidazolium as the linkers. Surprisingly, these naphthotubes show stronger binding affinities to neutral aromatic hydrocarbons in CD₃CN than in CD₂Cl₂.

Temperature-induced large amplitude conformational change in the complex of oxatub[4]arene revealed via rotaxane synthesis

Oxatub[4]arene was revealed via rotaxane synthesis to show a large amplitude conformational response to temperature change.