Dioxamethylene intramolecular bridging of p-tert-butylcalix[8]arene

The first examples of dioxamethylene bridged calix[8]arenes 2-6 have been obtained by Cs₂CO₃-promoted direct O-alkylation of p-tert-butylcalix[8]arene with BrCH₂Cl. Assignment of the 1,2-, 1,2:3,4-, 1,2:3,4:6,7-, 1,4:2,3:5,6:7,8-, and 1,2:3,4:5,6:7,8-bridging pattern of 2-6, respectively, was mainly based on chemical shift of OH groups and chemical correlations. Dynamic ¹H NMR studies and MM3 calculations indicated that in these compounds the dioxocine subunit adopts a boat-chair conformation.     

Synthesis and dichromate anion extraction ability of p-tert-butylcalix[4]arene diamide derivatives with different binding sites

The article describes the synthesis and evaluation of the dichromate anion (Cr₂O₇²⁻/HCr₂O₇⁻) extraction properties of p-tert-butylcalix[4]arene diamide derivatives (5-7) containing different binding sites. Among these compounds, 6 and 7 have been synthesized via aminolysis in a toluene-methanol solvent system with 3-aminomethylpyridine and 3,6-dioxa-1,8-diamino octane, respectively. On the other hand, compound 5 has been synthesized via an acid chloride method due to its inefficiency under aminolysis. The extraction properties of these diamides toward dichromate anions are studied by liquid-liquid extraction. The results show that p-tert-butylcalix[4]arene diamide derivative 7 exhibited a much higher affinity toward dichromate anions than that of 6 due to its special structure, while 5 was an ineffective ligand for these anions.     

Regioselective double intramolecular bridging of p-tert-butylcalix[7]arene

The first examples of doubly bridged calix[7]arenes 2a-h have been obtained by base-promoted O-alkylation of p-tert-butylcalix[7]arene 1 or 1,4-tetramethylene-bridged calix[7]arene 3a with a variety of bis-electrophiles including BrCH₂Cl, oligoethylene glycol ditosylates, and 1,2-bis(bromomethyl)benzene. In the presence of Cs₂CO₃ as the base, in acetone, the syn-1,4:2,3-bis-bridged regioisomer was obtained in yields up to 76%. Assignment of bridging pattern was based on chemical shift of OH groups in conjunction with chemical correlations with known compounds. Stereochemical and conformational features were investigated with the aid of 2D and Dynamic NMR studies and MM3 calculations.     

Thermo gravimetric analysis of supramolecular complexes of p-tert-butylcalix[6]arene and ammonium cations: crystal structure of diethylammonium complex

Thermo gravimetric analysis of ammonium-p-tert-butylcalix[6]arene salts were carried out to determine the stoichiometry of the inclusion compounds and the temperature of leaving of the ammonium cation, as amine, from the solid phase by a reverse proton transfer reaction to calixarene. The chain length of the amine molecules and their relative basicity order are the main factors which determine the decomplexation temperatures for the ammonium salts of piperidinium, diethylammonium, ethylenediammonium, morpholinium, s-butylammonium, butylammonium, hexylammonium and triethylammonium salts of p-tert-butylcalix[6]arene anion. The solid state structure of bis-diethylammonium-p-tert-butylcalix[6]arene dianion is reported. The calix moiety adopts a 1,2,3 alternate conformation, with one ammonium as exo-calix and other as endo-calix, with an intricate array of hydrogen bonds between phenol, phenolate and ammonium cations.     

exo and endo Isomerism of subvalent tin and germanium complexes derived from 1,3-diethers of p-tert-butylcalix[4]arene

A series of germanium and tin complexes of calix[4]arene diethers, namely [Calix^t-Bu(O)₂(OR)₂]M, has been prepared by the reaction of [Calix^t-Bu(OH)₂(OR)₂] with M[N(SiMe₃)₂]₂ (M = Ge, Sn; R = Me, CH₂Ph, CH₂C₆H₄Bu^t, SiPr₃ⁱ). X-ray diffraction studies demonstrate that [Calix^t-Bu(O)₂(OR)₂]M exist as exo and endo isomers in which the metal is, respectively, located either outside or inside the calixarene cavity. The exo isomer is considered to be the kinetic product, whereas the endo isomer is thermodynamically more stable. The ability to access endo-[Calix^t-Bu(O)₂(OR)₂]M, however, depends critically on the nature of R and M.     

Diester intrabridging of p-tert-butylcalix[8]arene and unexpected formation of the monospirodienone derivative

Reaction of p-tert-butylcalix[8]arene 1 with adipoyl chloride in the presence of NaH as the base yielded singly and doubly intrabridged esters 2-4 and 6. Surprisingly, calix[8]arene monospirodienone derivative 7 was also isolated, which was originated by O₂ oxidation. The conditions of this oxidation were optimized leading to a novel synthetic approach to calixarene monospirodienones based on the O₂/NaH/acyl-chloride oxidizing system. Xantheno calix[8]arenes 8-8a were obtained by rearrangement of 7.     

Hg-selective fluoroionophore of p-tert-butylcalix[4]arene-diaza-crown ether having pyrenylacetamide subunits

A new ionophore having two pyrenylacetamide moieties based on the p-tert-butylcalix[4]arene-diaza-crown ether has been prepared and its fluoroionophoric properties were investigated. Bis(pyrenyl) derivative was found to exhibit selective ON-OFF type sensing behavior toward Hg²⁺ ions over other representative transition and heavy metal ions. The fluorescence quenching efficiency of larger than 20-fold was observed with 100 equiv of Hg²⁺ ions and the association constant was found to be 4.5 × 10⁴ M⁻¹ in methanol. The ionophore also exhibited a very efficient quenching of excimer fluorescence selectively upon treatment with Hg²⁺ ions in 50% aqueous methanol solution. The observed Hg²⁺-selective ON-OFF type fluorescence behavior could be utilized as efficient sensing and switching devices for the design of other supramolecular systems.     

Preparation and characterization of p-tert-butylcalix[8]arene bonded capillaries for open-tubular capillary electrochromatography

p-tert-Butylcalix[8]arene bonded capillaries for open-tubular capillary electrochromatography were prepared with γ-glycidoxypropyltrimethoxysilane as a bridge. The bonded capillary displayed low and steady electroosmotic flow (EOF) values over the pH range from 4 to 9. Detection limits for direct spectrophotometric detection at 277 nm for benzenediols (at a signal to noise ratio of 2) were 0.96 mg l⁻¹ for the unbonded capillary and 1.48 mg l⁻¹ for the bonded capillary, showing that the bonded layer did not show significant absorbance and hence decreased sensitivity. The bonded capillaries showed good separation selectivity for o-, m- and p-benzenediols, α- and β-naphthols, and α- and β-naphthylamines. This selectivity was attributed to significant interactions between the analytes and the bonded p-tert-butylcalix[8]arene, which contributed to the electrochromatographic separation mechanism. The bonded capillaries gave high stability and reproducibility.     

Facile synthesis of thiacalix[n]arenes (n=4, 6, and 8) consisting of p-tert-butylphenol and methylene/sulfide alternating linkage and metal-binding property of the n=4 homologue

2,14-Dithiacalix[4]arene 3₄ was conveniently prepared in 16% yield by acid-catalyzed cyclocondensation of 2,2^′-thiobis[4-tert-butylphenol] with formaldehyde. The present method also afforded the first isolation of the analogues with six and eight phenol units, 3₆ (10%) and 3₈ (5%), respectively. Solvent extraction showed that 3₄ had high selectivity toward Cu²⁺ ion at pH 5.5 by coordination of the bridging sulfur with cooperative donation of the adjacent phenolate oxygens.     

Chromened t-butylcalix[4]arenes: cooperation effect of chromene and calixarene moieties on photochromism and metal-ion binding ability

Novel t-butylcalix[4]arenes bearing several chromene molecules were synthesized, and their photochromism and metal-ion binding ability were examined with alkali and alkaline-earth metal ions. While the metal-ion binding ability of the t-butylcalix[4]arene moiety facilitated the photoisomerization of the chromene moiety to a great extent, the chromene moiety influenced the metal-ion binding ability of the t-butylcalix[4]arene moiety through lariat effect. Therefore, the metal-ion that induced the most facilitated photoisomerization of the chromene moiety was shifted drastically from Li⁺ to Ba²⁺ with the increase of the incorporated chromene number. Even without metal ions, the interaction among the chromene moieties derived from the cone-conformation of the t-butylcalix[4]arene moiety also facilitated the photoisomerization.     

Synthesis of a distanna [2]ferrocenophane and reactivity of [2]ferrocenophanes towards elemental sulfur and selenium

Here we report the synthesis and crystal structure of a new [2]ferrocenophane [Fe(η⁵-C₅H₄)₂(SntBu₂)₂] with a sterically demanding distannanediyl bridge. The reactivity of the title compound towards selected main group elements was examined and in addition, this reactivity pattern was established for the related diboranediyl bridged [2]ferrocenophane [Fe(η⁵-C₅H₄)₂(BNMe₂)₂].     

Complexation of trivalent lanthanoid ions with 4-benzoyl-3-phenyl-5-isoxazolone and p-tert-butylcalix[4]arene fitted with phosphinoyl pendant arms in solution during synergistic solvent extraction and structural study of solid complexes by IR and NMR

The liquid extraction of 14 lanthanoids with a 4-benzoyl-3-phenyl-5-isoxazolone (HPBI) alone in CHCl₃ as a diluent from perchlorate medium at constant ionic strength μ = 0.1 is investigated. The synergistic solvent extraction of five selected lanthanoid ions (La³⁺, Nd³⁺, Eu³⁺, Ho³⁺ and Lu³⁺) with 4-benzoyl-3-phenyl-5-isoxazolone (HPBI) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis-(dimethylphosphinoylmethoxy)calix[4]arene, (S) in CHCl₃ has been studied too. The stoichiometry of the extracted species was characterised by a classical log–log plot analysis. It was found that the composition of the extracted species with HPBI are Ln(PBI)₃ and in the presence of the phosphorus-containing calix[4]arene the lanthanoid ions have been extracted as [Ln(PBI)₃S₂]. The values of the equilibrium constants and the separation factors have been calculated. The influence of the synergistic agent on the extraction process has been discussed.     

State of water in CB[6] and CB[8] cavitands

The state of water in cucurbiturils CB[6] and CB[8], which were synthesized in hydrochloric acid solutions of glycoluril and formaldehyde, was studied. The amount of water coordinated in the macrocycle cavity and on its portals was shown to depend on the moisture content of the medium, being 2.4 molecules per 1 molecule of CB[6] and 3.2 per 1 molecule of CB[8], and in CB[8] coordinated water exists in two energy states. The state with the vaporization parameters Δ_vap H ^○ _381.5 = 29.2±0.4 kJ mol^?1 and Δ_vap S ^○ _381.5 = 50.7±1.0 J mol^?1 K^?1 coincides with the state of water in CB[6]. For another state, the vaporization parameters are Δ_vap H ^○ ₃₇₃ = 31.7±0.5 kJ mol^?1 and Δ_vap S ^○ ₃₇₃ = 63.2±1.2 J mol^?1 K^?1. The number of molecules bound to the oxygen atoms of the macrocycle portals is 1.7 and 2.6 for CB[6] and CB[8], respectively.     

Regioselective ipso formylation of p-tert-butylcalix[4]arene

A convenient procedure for direct introduction of one formyl group into p-tert-butylcalix[4]arenes through ipso substitution is described.     

Design and synthesis of self-included pillar[5]arene-based bis-[1]rotaxanes

Two strategies for the design of new pillar[5]arene-based mechanically self-interlocked molecules (MSMs) are reported here. The first strategy is based on the construction of an intermediate pseudo[1]rotaxane followed by the desired bis-[1]rotaxane. The other one is based on the construction of the desired bis-[1]-rotaxane directly via a condensation reaction through host-guest interactions between a mono-functionalized pillar[5]arene and the axle. This compound has interesting self-assembly properties in methanol and some extended applications of this compound will be reported in the near future.     

Synthesis and stereochemical resolution of functional [5]pericyclynes

Three different kinds of ring carbo-mers of [5]cyclitol ethers were targeted as challenging examples of functional [5]pericyclynes. Three tertiary pentaaryl-carbo-[5]cyclitol methyl ethers were synthesized through a [11+4] ring-closing double addition of triphenyl- and tri-p-anisyl-undecatetrayn-diides to dibenzoylacetylene. These compounds, obtained as oily mixtures of stereoisomers, are stable and can behave as acetylenic ligands of one or two Co₂(CO)₆ units. NMR analysis reveals that the broad diasteroisomeric dispersity of a triether, is consistently reduced in the symmetrized pentaether. Three bis-secondary triaryl-carbo-[5]cyclitol methyl ethers with adjacent CH(OR) vertices were synthesized through a similar [11+4] ring-closing process, where the same tetrayn-diides add to both the carbaldehyde ends of the (η²-OCH-CC-CHO)Co₂(CO)₆ complex. Despite the possibility of tautomeric isomerization, the occurrence of two adjacent bis-propargylic carbinol vertices does not diminish the stability of the [5]pericyclyne framework. Finally, two bis-secondary carbo-[5]cyclitol methyl ethers with non-adjacent CH(OH) vertices were synthesized through an alternative [10+5] ring-closing process. The bis-secondary carbo-[5]cyclitols are regarded as isohypsic equivalents of the challenging [C,C]₅carbo-cyclopentadienyl cation. A diphenyl-hexaoxy-[5]pericyclyne with two non-adjacent secondary carbinol vertices was also prepared through a [10+5] ring-closing strategy: this molecule is an isohypsic equivalent of the previously calculated zwitterionic carbo-cyclopentadienone, which could be observed as a DCI/NH₃-MS fragment after treatment with SnCl₂/HCl. Analytical HPLC showed that the C₁₁ triphenyl-undecatetrayne precursor of the [11+4] strategy was obtained as a statistical 1:2:1 mixture of the three possible diastereoisomers. Semi-preparative HPLC allowed for the resolution of this mixture. The pure major diastereoisomer was employed to prepare a partly resolved sample of pentamethoxy-pentaphenyl-[5]pericyclyne. Analytical HPLC showed that the latter corresponds to the statistical distribution of the expected three residual diastereoisomers. Semi-preparative HPLC finally afforded samples of diastereoisomerically pure pentamethoxy-[5]pericyclyne as crystalline solids.     

Generation of oxodiazonium ions 3. Synthesis of [1,2,5]oxadiazolo[3,4-c]cinnoline-1,5-dioxides

A reaction of 4-(N-nitramino)-3-phenylfuroxane with the Ac₂O/H₂SO₄ system leads to the formation of [1,2,5]oxadiazolo[3,4-c]cinnoline-1,5-dioxide, the first representative of furoxanocinnolines. The reaction presumably proceeds through the transformation of the nitramine fragment NHNO₂ to the oxodiazonium ion [N=N=O]⁺ with subsequent intramolecular attack by this cation on the phenyl ring. Furoxanocinnoline is also formed in the reaction of the 4-(N-nitramino)-3-phenylfuroxane O-methyl derivative with H₂SO₄. It is assumed that this reaction also proceeds with involvement of the intermediate cation [N=N=O]⁺ formed by the protonation of the N=N(O)OMe group and subsequent elimination of MeOH. 7-Nitro derivative is formed when furoxanocinnoline is nitrated with the concentrated HNO₃/H₂SO₄ mixture. The compounds obtained were characterized by ¹H, ¹³C, and ¹⁴N NMR spectroscopy.     

Zur frage transanularer II-II-wechselwirkungen im [2.2]metacyclophan, [2.2]Paracyclophan und 2,2′-spirobiindan

Concerning the question of transanular II-II-interactions in [2.2]metacyclophane, [2.2]paracyclophane and 2,2′-spirobiindane.From the quotient of the two dissociation constants (K₁/K₂) of [2.2]metacyclophane-bis-chromtricarbonyl (9·0 ± 1·9) it was concluded that there are no transanular II-II-interactions between the two benzene rings. The corresponding values for the bis-chromtricarbonyl-complexes of 2,2′-spirobiindane and [2.2]paracyclophane are 8·0 ± 1·5 and 10⁴, resp. These results are supported by IR-spectroscopical data of the CO-frequencies of the Cr(CO)₃-complexes of [2.2]metacyclophane and some derivatives, of 2,2′-spirobiindane and [2.2]paracyclophane.Moreover, UV-spectroscopic studies of tetracyanoethylene complexes of arenes are shown to be insignificant with regard to transanular II-II-interactions.     

Nitrochlorination of methyl tricyclo[4.1.0.02,7]heptane-1-carboxylate and phenyl tricyclo[4.1.0.02,7]hept-1-yl sulfone

Treatment of methyl tricyclo[4.1.0.0^2,7]heptane-1-carboxylate and phenyl tricyclo[4.1.0.0^2,7]hept-1-yl sulfone with a ～1:8 mixture of N₂O₄ and NOCl in diethyl ether at ?5 to 0°C gave products of formal anti-addition of NO₂Cl at the central C¹-C⁷ bond. In the reaction with phenyl tricyclo[4.1.0.0^2,7]hept-1-yl sulfone nitryl chloride acts as an effective chlorinating agent; as a result, a mixture of diastereoisomeric syn- and anti-6,7-dichlorobicyclo[3.1.1]hept-6-yl phenyl sulfones at a ratio of 7.5:1 is formed.     

Rapid ‘on-column’ preparation of hydrogen [11C]cyanide from [11C]methyl iodide via [11C]formaldehyde

Hydrogen [¹¹C]cyanide ([¹¹C]HCN) is a versatile ¹¹C-labelling agent for the production of ¹¹C-labelled compounds used for positron emission tomography (PET). However, the traditional method for [¹¹C]HCN production requires a dedicated infrastructure, limiting accessibility to [¹¹C]HCN. Herein, we report a simple and efficient [¹¹C]HCN production method that can be easily implemented in ¹¹C production facilities. The immediate production of [¹¹C]HCN was achieved by passing gaseous [¹¹C]methyl iodide ([¹¹C]CH₃I) through a small two-layered reaction column. The first layer contained an N-oxide and a sulfoxide for conversion of [¹¹C]CH₃I to [¹¹C]formaldehyde ([¹¹C]CH₂O). The [¹¹C]CH₂O produced was subsequently converted to [¹¹C]HCN in a second layer containing hydroxylamine-O-sulfonic acid. The yield of [¹¹C]HCN produced by the current method was comparable to that of [¹¹C]HCN produced by the traditional method. The use of oxymatrine and diphenyl sulfoxide for [¹¹C]CH₂O production prevented deterioration of the molar activity of [¹¹C]HCN. Using this method, compounds labelled with [¹¹C]HCN are now made easily accessible for PET synthesis applications using readily available labware, without the need for the ‘traditional’ dedicated cyanide synthesis infrastructure.

In a reaction column, gaseous [¹¹C]methyl iodide was converted to [¹¹C]formaldehyde in a first layer containing N-oxide and then transformed into hydrogen [¹¹C]cyanide in a second layer containing hydroxylamine-O-sulfonic acid within 2 minutes.