Crystal Structures of Uranyl Ion Complexes of Tetrahydroxy[3.1.3.1]metacyclophane (Homocalix[4]arene)

The first crystal structures of complexes of tetrahydroxy-[3.1.3.1]metacyclophanes, also termed homocalix[4]arenes, are reported. In the two uranyl ion complexes obtained, with different para-substituents, the complex core is analogous to that in tetrahomodioxacalix[4]arene complexes, with the cation in a tetra-phenoxide, distorted square-planar environment. The packing in one of these complexes comprises two different arrangements, one of them being a columnar stacking of complex molecules with sandwiched triethylammonium counter-ions hydrogen bonded to one complex and held by cation–π and CH–π interactions within the cavity of the other neighbouring one.     

Efficient synthesis of copillar[5]arenes and their host-guest properties with dibromoalkanes

An efficient method for the synthesis of copillar[5]arenes was developed with FeCl(3) as catalyst and different 1,4-dialkoxybenzenes and paraformaldehyde as reactants (yields: 50-85%). The host-guest property of (co)pillar[5]arenes and terminal dibromoalkanes was investigated by (1)H NMR measurements and an X-ray study. The complexation behavior of the copillar[5]arenes can be tuned by changing the substituents on the host. A complete complexation selectivity was found between pillar[5]- and pillar[6]arenes, which is an interesting aspect for sensor techniques.     

柱芳烃的合成及主客体化学研究进展

柱芳烃是由对苯二酚或对苯二酚醚通过亚甲基桥在苯环的对位连接而成的一类环状低聚物, 是一类新型的大环主体分子. 本文介绍了柱芳烃和功能化柱芳烃分子的合成, 以及在分子识别、 自组装等主客体化学方面的最新研究进展, 并对其研究前景进行展望.     

Synthesis of novel pillar-shaped cavitands “Pillar[5]arenes” and their application for supramolecular materials

In 2008, we reported a new class of macrocyclic hosts and named “Pillar[5]arenes”. They combine the advantages and aspects of traditional hosts and have a composition similar to those of typical calix[n]arenes. Pillar[5]arenes have repeating units connected by methylene bridges at the para-position, and thus they have a unique symmetrical pillar architecture differing from the basket-shaped structure of meta-bridged calix[n]arenes. Pillar[5]arenes show high functionality similar to cyclodextrins, and can capture electron accepting guest molecules within their cavity similarly to cucurbit[n]urils. In this review, the synthesis, structure, rotation, host–guest properties, planar chirality and functionality of pillar[5]arenes are discussed, along with pillar[5]arene-based supramolecular architectures and the challenges in synthesizing pillar[6]arenes.     

Synthesis of amine, halide, and pyridinium terminated 2-alkyl-p-tert-butylcalix[4]arenes

The synthesis of calix[4]arenes with functional groups tethered to a single methylene bridge has been explored. Mono-lithiated calix[4]arenes react with 1,ω-bromochloroalkanes to give 2-(ω-chloroalkyl)-calix[4]arenes, which function as key intermediates in the synthesis of a variety of tether-functionalized calix[4]arenes. Subsequent reactivity of these chloroalkyl species has allowed for successful synthesis of 2-(ω-iodoalkyl)-calix[4]arenes, 2-(ω-pyridiniumalkyl)-calix[4]arenes, and 2-(ω-aminoalkyl)-calix[4]arenes. This latter group of amine-terminated calix[4]arenes are especially significant as they may serve as useful entries to a wide range of subsequent chemistry, including metal coordination or attachment to a solid support. Both alkyl and aryl amines have been incorporated at the end of the tether, and a 2,6-diisopropylaniline derivative has been analyzed by X-ray diffraction.     

Monofunctionalized pillar[5]arene as a host for alkanediamines

Alkanediamines serve as neutral guests for the recently discovered host pillar[5]arene. The proposed [2]pseudorotaxane nature of the superstructure of the 1:1 host-guest complexes is supported by the template-directed synthesis of a related [2]rotaxane. A synthetic route to monofunctional pillar[5]arenes has also been developed, allowing for the creation of a fluorescent sensor for alkylamine binding. The precursors to this host could act as starting points for a large library of monofunctional pillar[5]arene macrocycles.     

Construction of π‐Surface‐Metalated Pillar[5]arenes which Bind Anions via Anion–π Interactions

By simple ligand exchange of the cationic transition‐metal complexes [(Cp*)M(acetone)₃](OTf)₂ (Cp*=pentamethylcyclopentadienyl and M=Ir or Rh) with pillar[5]arene, mono‐ and polynuclear pillar[5]arenes, a new class of metalated host molecules, is prepared. Single‐crystal X‐ray analysis shows that the charged transition‐metal cations are directly bound to the outer π‐surface of aromatic rings of pillar[5]arene. One of the triflate anions is deeply embedded within the cavity of the trinuclear pillar[5]arenes, which is different to the host–guest behavior of most pillar[5]arenes. DFT calculation of the electrostatic potential revealed that the metalated pillar[5]arenes featured an electron‐deficient cavity due to the presence of the electron‐withdrawing transition metals, thus allowing encapsulation of electron‐rich guests mainly driven by anion–π interactions.     

Calix[4]arenes bearing a tropylium substituent as hosts for organic cations

Four novel calix[4]arenes bearing one cycloheptatrienyl substituent and two calix[4]arenes with one tropylium substituent at the wider rim were synthesized. Cycloheptatrienyl- and tropylium-calixarenes represent two states of a potentially photoswitchable calixarene host. The complexation of selected hosts with organic cations such as quinolinium, ammonium and tropylium ions was studied. It was found that the complexation of organic cations by the tropylium-substituted host was much stronger in CDCl₃ solution than by the related cycloheptatrienyl-host. Aryltropylium ions are bound by tropylium hosts. Accordingly, dimers of the host itself are formed both in CDCl₃ solution and in the gas phase. Because of the intramolecular charge transfer tropyliumcalix[4]arenes are qualified as chromogenic hosts. These undergo two acid-base equilibriums depending on the concentration and the solvent. Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Synthesis and disproportionation of ABAC-type oxacalix[4]arenes

An efficient method to prepare ABAC-type oxacalix[4]arenes by a ‘3+1’ fragment synthesis and their CsF-catalyzed disproportionation producing an equilibrium mixture of three oxacalix[4]arenes are described.     

Complexation of fullerenes by calix[n]arenes: molecular dynamic simulations and benesi-hildebrandequilibrium constants

MD simulations using a combination of AMI and AMBER are performed to elucidate the origin of complexation between fullerenes and calix[n]arenes (n = 4,6,8). Only calix[6]arenes and calix[8]arenes are suitable for complex formation. By introducing benzyl substitutents on the upper rim of the calixarenes the interaction energy between host and guest is even improved. Analysis of the data also reveals a strong stabilization by t-butyl or benzyl substitutents beside π-π interactions between the arene units of the calixarene and fullerenes. The calculated data perfectly correlate with the experimentally observed equilibrium constants.     

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.     

A convergent synthesis of Hexahomotriazacalix

A new, convergent synthesis of hexahomotriazacalix[3]arenes 1a-e is described. The key transformation in this synthesis involves the coupling of the triamines 4a-d with 2, 6-bis(chloromethyl)-4-methylphenol 5 and results in the formation of the hexahomotriazacalix[3]arenes 1a-d in 90-95% yield. The triamines 4a-d were constructed by the one-pot reaction of monochloroaldehyde 3 and a primary amine followed by reduction to yield the triamines 4a-d in 50-55% yield. Deallylation of macrocycle 1d was accomplished by palladium catalysis to obtain the N-unsubstituted macrocycle 1e, which has the potential to be a precursor to a variety of N-substituted hexahomotriazacalix[3]arenes.     

Calixarene-Based Dendrimers. A Timely Review

This timely review focuses on the synthesis of dendrimers from calix[4]arenes and thiacalix[4]arenes. Some interesting features of these calix-dendrimers are given.     

Alkylation of narrow rim calix[4]arenes in a DMSO-NaOH medium

An effective method of 5,11,17,23-tetra-tert-butyl-25,26-dialkoxy-27,28-dihydroxy-calix[4]arenes and 25,26,27,28-tetraalkoxycalix[4]arenes synthesis by alkylation of tetrahydroxycalix[4]arenes in a DMSO-NaOH medium was developed.     

Azocalixarenes.8: synthesis and investigation of the absorption spectra of di-substituted azocalix[4]arenes containing chromogenic groups

The synthesis of series of chromogenic di-substituted azocalix[4]arene derivatives is described. A ketone moiety as a different chelating agent is grafted on the lower rim of p-tert-butylcalix[4]arenes. Eight novel azocalix[4]arenes (1–8) are prepared by linking 2-, 3- and 4-nitroaniline, 4-phenylazoaniline, 3- and 4-chloroaniline or 2- and 4-methylaniline to 25,27-diacetonyloxy-26,28-dihydroxy-11,23-di-(tert-butyl)calix[4]arene through a diazo-coupling reaction, and characterized by UV–Vis, FT-IR and ¹H-NMR spectroscopic techniques and elemental analysis, consecutively. The absorption spectra of the di-substituted azocalix[4]arenes are discussed, according to effect of varying pH and solvent upon the absorption ability of azocalix[4]arenes. The colors of these azocalix[4]arenes are compared with respect to nature of their aromatic rings and substituents there in. Concentration effects on the visible absorption maxima of these compounds are also reported.     

Synthesis and host-guest properties of pillar[6]arenes

A facile method for the synthesis of pillar[6]arenes was developed.A series of pillar[6]arenes were prepared with FeCl 3 as catalyst and chloroform as solvent at room temperature in moderate yields(30%-40%).Their host-guest properties with n-cetyltrimethyl ammonium bromide were investigated by 1 HNMR.The results showed that high selectivity in the host-guest relationship became apparent between pillar[6]arenes and pillar[5]arenes based on the different size of the inner cavity.     

Alkylation of narrow rim calix[4]arenes in a DMSO-NaOH medium

An effective method of 5,11,17,23-tetra-tert-butyl-25,26-dialkoxy-27,28-dihydroxy-calix[4]arenes and 25,26,27,28-tetraalkoxycalix[4]arenes synthesis by alkylation of tetrahydroxycalix[4]arenes in a DMSO-NaOH medium was developed.     

Dynamic materials fabricated from water soluble pillar[n]arenes bearing triethylene oxide groups

Recent advance on dynamic materials fabricated from water soluble pillar[n]arenes with triethylene oxide groups was summarized.     

First synthesis of lower-rim-substituted aryl ethers of p-tert-butylcalix[4]arene

With the use of S(N)Ar or Ullmann reactions, the synthesis of the first lower-rim aryl ether derivatives of tert-butylcalix[4]arene is reported, as are some of their conformational properties, (1)H NMR spectra, and X-ray crystal structures. The lower-rim aryl pendants reported herein provide for new scaffolds upon which a host of other new molecular architectures can be constructed, thus extending the capability of the versatile calix[4]arenes even further.     

In situ generation of vinyl allenes and its applications to one-pot assembly of cyclohexene, cyclooctadiene, 3,7-nonadienone, and bicyclo[6.4.0]dodecene derivatives with palladium-catalyzed multicomponent reactions

A novel tandem Pd-catalyzed cross-coupling and [4 + 4] cycloaddition sequence allows the rapid synthesis of eight-membered carbocycles starting from alpha-bromovinyl arenes and propargyl bromides in one reaction vessel. It is noteworthy that four components are assembled into one molecule via this procedure. In contrast to alpha-bromovinyl arenes, alpha-bromovinyl alkanes afforded tandem cross-coupling and homo [4 + 2] cycloaddition products. Subjecting an equimolar mixture of alpha-bromostyrene and 2-bromo-1-octene to propargyl bromides furnished the tandem Pd-catalyzed cross-coupling and hetero [4 + 2] cycloaddition product. Exposure of equimolar mixtures of alpha-bromovinyl arenes to allenylindium resulted in tandem a Pd-catalyzed cross-coupling and hetero [4 + 4] cycloaddition products. Synthesis of vinylallene from the reaction of vinyl triflate with allenylindium followed by Pd-catalyzed carbon monoxide insertion reaction gave the corresponding 3,7-nonadienone product via tandem Pd-catalyzed cross-coupling and [4 + 4 + 1] annulation. Tandem Pd-catalyzed cross-coupling, [4 + 4] cycloaddition, and [4 + 2] cycloaddition provided the rapid synthesis of bicyclo[6.4.0]dodecene derivatives starting from alpha-bromovinyl arenes, propargyl bromides, and dienophiles in one operation, in which five components were integrated into one molecule.