Synthesis of Inherently Chiral Azacalix[4]arenes and Diazadioxacalix[4]arenes

Synthesis of Azacalixarenes and Development of Their Properties

This review focuses on the synthesis, structure, and interactions of metal ions, the detection of some weak interactions using the structure, and the construction of supramolecules of azacalixarenes that have been reported to date. Azacalixarenes are characterized by the presence of shallow or deep cavities, the simultaneous presence of a basic nitrogen atom and an acidic phenolic hydroxyl group, and the ability to introduce various side chains into the cyclic skeleton. These molecules can be given many functions by substituting groups on the benzene ring, modifying phenolic hydroxyl groups, and converting side chains. The author discusses the evidence of azacalixarene utilizing these characteristics.

Synthesis, structure, and anion binding of functional oxacalix[4]arenes

Oxacalix[4]arenes obtained from the highly efficient, one-pot S_NAr reaction were post-macrocyclization functionalized through the reduction of nitro groups and hydrolysis of the ester groups to obtain several derivatives of desired solubility. The difficulties in basic hydrolysis of ester groups were overcome via developing an acid hydrolysis method for tert-butyl ester derivatives of this class. The synthesis of symmetrical oxacalix[4]arenes from an unsymmetrically substituted precursor was also explored via a multiple step fragment coupling approach. Compounds 17 & 18 adopted 1,3-alternate conformations in the solid state as most oxacalix[4]arenes did, and a chair (zigzag) conformation was revealed for tetraamido oxacalix[4]arene (6a) by X-ray single crystal analysis. The tetraureido oxacalixarene (7) showed strong association towards various anions such as F^-, Cl^-, Br^-, I^-, Ac^-, and HSO₄^- with a 1 : 1 stoichiometry as revealed by ¹H NMR analysis and UV-vis measurements.

Multi-point interaction-based recognition of fluoride ions by tert-butyldihomooxacalix[4]arenes bearing phenolic hydroxyls and thiourea

A series of p-tert-butyldihomooxacalix[4]arenes bearing phenolic hydroxyls and thiourea moieties were prepared to investigate their anion binding behavior.

Lone pair–π vs. σ-hole–π interactions in bromine head-containing oxacalix[2]arene[2]triazines

New bromine head-containing oxacalix[2]arene[2]triazines were synthesized. Owing to the bromine head and complementary V-shaped cavity, the solid state structure showed an intriguing and unique 1D-supramolecular chain-like self-assembly.

N1-(5-Fluoro-2,4-dinitrophenyl)-N2-phenyl-4-(trifluoromethyl)benzene-1,2-diamine

Treating 1,5-difluoro-2,4-dinitrobenzene (1) with N1-phenyl-5-(trifluoromethyl)benzene-1,2-diamine (4) and N,N-diisopropylethylamine in EtOH at ca. 0 °C for 4 h affords a mixture of N1-(5-ethoxy-2,4-dinitrophenyl)-N2-phenyl-4-(trifluoromethyl)benzene-1,2-diamine (5) (38%) and N1-(5-fluoro-2,4-dinitrophenyl)-N2-phenyl-4-(trifluoromethyl)benzene-1,2-diamine (6) (51%) that can be separated by chromatography. Repeating the reaction in dichloromethane led to the sole formation of N1-(5-fluoro-2,4-dinitrophenyl)-N2-phenyl-4-(trifluoromethyl)benzene-1,2-diamine (6) in 96% yield.

Synthesis of hydroxylated azacalix[1]arene[3]pyridines from hydrolysis of high valent arylcopper complexes and conversion to a double azacalix[1]arene[3]pyridine host molecule

Arylcopper(ii) compounds reacted efficiently with KOH at ambient temperature to produce exclusively lower-rim-hydroxylated azacalix[1]arene[3]pyridines which underwent further CuCl₂/TMEDA-catalyzed oxidative homocoupling to afford an unprecedented bisazacalix[1]phenol[3]pyridine host molecule.

Straightforward metal-free synthesis of an azacalix[6]arene forming a host–guest complex with fullerene C60

The straightforward metal-free synthesis of an azacalix[6]arene from simple aryl units is described together with its full characterization. This macrocycle features a rare 1,2,4,5-alternate conformation and is able to form a 1 : 1 stable host–guest complex with C₆₀.

Azacalix[2]arene[2]carbazoles: synthesis, structure and properties

A new type of –NH– bridged azacalix[2]arene[2]carbazoles has been synthesized by aromatic nucleophilic substitution reactionviaone pot and/or fragment coupling strategy.

Synthesis of trifluoromethylthiolated azacalix[1]arene[3]pyridines from the Cu(ii)-mediated direct trifluoromethylthiolation reaction of arenes via reactive arylcopper(iii) intermediates

Cu(ii)-mediated arene C–H bond trifluoromethylthiolation with Me₄NSCF₃proceedsviaarylcopper(iii) intermediates to produce functionalized azacalix[1]arene[3]pyridine macrocycles.

Selective Formylation of Azacalixpyridine Macrocycles and Their Transformation to Molecular Semicages

The aromatic electrophilic formylation reaction of azacalix[2]arene[2]pyridine and azacalix[4]pyridine were systematically studied. By simply controlling the ratio of reactants and the reaction temperature, the Vilsmeier-Haack reaction selectively afforded mono-, di-, and tetra-formylated azacalix[2]arene[2]pyridines and azacalix[4]pyridines. The preferential and selective functionalization reactions of macrocycles were discussed in terms of their conformational structure and conjugation effect between aromatic subunits and bridging nitrogen atoms. All resulting functionalized azacalix[2]arene[2]pyridines and azacalix[4]pyridines adopted a 1,3-alternate conformation both in the crystalline state and in solution. Taking advantage of the close proximity of aldehyde groups in 1,3-alternate di- and tetra-formylated azacalixpyridine macrocycles, the McMurry reductive coupling reaction of carbonyls was accomplished to yield unique semicage molecules.

Synthesis and conformational studies of chiral macrocyclic [1.1.1]metacyclophanes containing benzofuran rings

A novel hemisphere-shaped inherently chiral calixarene analogoue [1.1.1]metacyclophane containing both benzene and benzofuran rings was synthesized by fragment coupling approach.

Nitrogen and oxygen bridged calixaromatics: synthesis, structure, functionalization, and molecular recognition

Pedersen, Lehn, and Cram established supramolecular chemistry through their pioneering work with crown ethers, cryptands, and spherands. Since then, the hallmark of supramolecular science has been an increasing sophistication in the design and construction of macrocyclic molecules, as manifested in cyclodextrin derivatives, calixarenes, resorcinarenes, cyclotriveratrylenes, cucurbiturils, calixpyrroles, cyclophanes, and many other examples. Indeed, macrocyclic compounds provide unique models for the study of noncovalent molecular interactions. They also constitute building blocks for constructing high-level molecular and supramolecular architectures and fabricating molecular devices and advanced materials. As a postgraduate in the Huang laboratory in the late 1980s, I became interested in the calix[n]arenes because of their unique conformational structures and versatile complexation properties. The notion of introducing heteroatoms, and particularly nitrogen, into the bridging position of conventional calixarenes was particularly intriguing. Nitrogen, unlike methylene, can adopt either an sp(2) or sp(3) electronic configuration, providing different conjugation systems with adjacent aromatic rings. Consequently, depending on the configuration and conjugation, a range of C-N bond lengths and C-N-C bond angles is possible. The conformation and cavity size in heteroatom-bridged calixarenes might thus be tuned through the bridging heteroatoms and the number of aromatic rings. Furthermore, because heteroatom linkages significantly affect the electron density and distribution on aromatic rings, the electronic features of macrocyclic cavities might be regulated by heteroatoms. Given the essentially limitless combinations possible, only synthetic hurdles would prevent access to numerous diverse heteracalixaromatics. We began a systematic study on nitrogen- and oxygen-bridged calixarenes in 2000, years later than originally envisioned. Before this study, very few heteracalixaromatics had been reported, owing to the formidable synthetic challenges involved. Apart from thiacalixarene, the synthesis of nitrogen- and oxygen-bridged calixarenes appeared very difficult. But since our first publications in 2004, we have been delighted to see the rapid and tremendous development of the supramolecular chemistry of this new generation of macrocycles. In this Account, I summarize the synthesis of N- and O-bridged calixaromatics and their regiospecific functionalization on the rims and bridging positions, focusing on the fragment coupling approach and contributions from our laboratory. I describe the construction of molecular cages based on heteracalixaromatics and discuss the effect of both bridging heteroatoms and substituents on macrocyclic conformations and cavity sizes. Molecular recognition of neutral organic molecules and charged guest species is also demonstrated. The easy accessibility, rich molecular diversity, unique conformation, and cavity tunability of heteracalixaromatics make them invaluable macrocycles for research in supramolecular chemistry. New heteracalixaromatics, with well-defined conformations and cavity properties, will provide powerful tools for probing noncovalent interactions, leading to the development of new molecular sensing and imaging systems. Multicomponent molecular self-assembly of heteracalixaromatics as functional modules with metals, metal clusters, or charge-neutral species should result in multidimensional solid and soft materials with diverse applications. The profitable incorporation of heteracalixaromatics into molecular devices can also be anticipated in the future. Moreover, the construction of enantiopure, inherently chiral heteracalixaromatics should provide important applications in chiral recognition and asymmetric catalysis.

1,5-Dichloro-3(2,7),7(2,7)-dinaphthal-ena-2,4,6,8-tetra-oxa-1(2,6),5(2,6)-di(1,3,5-triazina)octa-phane

In the macrocyclic title compound, C(26)H(12)Cl(2)N(6)O(4), an O-atom-bridged calix[2]naphthalene-[2]triazine synthesized using a one-pot approach from naphthalene-2,7-diol and cyanuric chloride, the two isolated naphthalene planes and the two triazine-2,6-di-oxy planes adopt a 1,3-alternate configuration, with a dihedral angle of 84.10 (8)° between the naphthalene rings and a dihedral angle of 39.02 (14)° between the triazine rings. In the crystal, weak inter-molecular π-π stacking inter-actions are found between face-to-face naphthalene rings [centroid-centroid distance = 3.662 (7) Å].