Nucleophilic addition to benzo[b]thieno[2,3-b]benzo[b]thiophene S,S,S′,S′-tetroxide

The reaction of benzo[b]thieno[2,3-b]benzo[b]thiophene S,S,S′,S′-tetroxide with primary and secondary amines and with alcohols gave 10 b-amino- and 10 b-alkoxy-5a, 10b-dihydro-benzo[b]thieno[2,3-b]benzo[b]thiophene S,S,S′,S′-tetroxides. These nucleophilic reagents do not add to benzo[b]thieno[2,3-b]benzo[b]thiophene S,S-dioxide.     

Mechanism of the conversion of inverted CB[6] to CB[6

Inverted cucurbit[n]urils (iCB[n]) form as intermediates during the synthesis of cucurbit[n]urils from glycoluril and formaldehyde in HCl (85 degrees C). Product resubmission experiments establish that the diastereomeric iCB[6] and iCB[7] are kinetic products that are less stable thermodynamically than CB[6] or CB[7] (>2.8 kcal mol(-1)). When iCB[6] or iCB[7] is heated under aqueous acidic conditions, a preference for ring contraction is noted in the formation of CB[5] and CB[6], respectively. Interestingly, under anhydrous acidic conditions ring size is preserved with iCB[6] delivering CB[6] cleanly. To establish the intramolecular nature of the iCB[6] to CB[6] conversion under anhydrous, but not aqueous, acidic conditions we performed crossover experiments involving mixtures of iCB[6] and its (13)C=O labeled isotopomer (13)C(12)-iCB[6]. An unusual diastereomeric CB[6] with a M?bius geometry (13) is proposed as a mechanistic intermediate in the conversion of iCB[6] to CB[6] under anhydrous acidic conditions. The improved mechanistic understanding provided by this study suggests improved routes to CB[n]-type compounds.     

Synthesis of 11C-labelled N,N'-diphenylurea and ethyl phenylcarbamate by a rhodium-promoted carbonylation via [11C]isocyanatobenzene using phenyl azide and [11C]carbon monoxide

The reaction with phenyl azide and [11C]carbon monoxide to give N,N'-diphenyl[11C]urea and ethyl phenyl[11C]carbamate has been studied with the aim of development of a new methodology for carbonylation using [11C]carbon monoxide with high specific radioactivity. The synthesis of 11C-labelled N,N'-diphenylurea from phenyl azide and [11C]carbon monoxide, with 1,2-bis(diphenylphosphino)ethane-bound Rh(I) complex at 120 degrees C at a pressure of 35 MPa in the presence of aniline was accomplished in 82% trapping efficiency and 82% conversion yield. This approach was also useful for the synthesis of ethyl phenyl[11C]carbamate with lithium ethoxide as a nucleophilic reagent giving 90% trapping efficiency and 76% conversion yield. These reactions can be considered to proceed via a [11C]isocyanate or a [11C]isocyanate-coordinated Rh complex to give the corresponding 11C-products. This protocol provides the chemical basis for the synthesis of [11C]urea and [11C]carbamate derived from [11C]isocyanates.     

Syntheses of some new azolopyrido‐[4′,3′:4,5]thieno[2,3‐d]pyrimidines

Diethyl 2‐[(ethoxythioxomethyl)amino]‐4,5,6,7‐tetrahydrothieno[2,3‐c]‐pyridine‐3,6‐dicarboxylate 2 , prepared from diethyl 2‐isothiocyanato‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridine‐3,6‐dicarboxylate 1 by boiling in anhydrous ethanol, was converted into pyrido[4′,3′:4,5]thieno[2,3‐d]pyrimidine derivatives 3, 4 by treatment with hydrazine hydrate. The tetracyclic systems imidazo[1,2‐a]pyrido‐[4′,3′:4,5]thieno[2,3‐d]pyrimidine 9 and pyrido[4′,3′:4,5]thieno[2,3‐d][1,3]thiazolo‐[3,2‐a]pyrimidine 10 were synthesized by the reaction of 2 with 1,2‐diaminoethane and aminoethanethiol, respectively. The hydrazino derivative 4 underwent cyclization reactions with orthoesters and nitrous acid to give the corresponding pyrido[4′,3′:4,5]thieno[2,3‐d][1,2,4]triazolo[1,5‐a]pyrimidines 5, 6 and pyrido[4′,3′:4,5]thieno[3,2‐e][1,2,3,4]tetrazolo[1,5‐a]pyrimidine 8 , respectively. Moreover, reactions of 3 with cyanogen bromide, N‐carbethoxyhydrazine, carbon disulfide, and ethylchloroformate resulted in the formation of the new pyrido[4′,3′:4,5]thieno[2,3‐d][1,3,4]thiadiazolo[3,2‐a]pyrimidine derivatives 12–15 . © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:280–286, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10030     

Water-soluble pillar[4]arene[1]quinone: Synthesis,host-guest property and application in the fluorescence turn-on sensing of ethylenediamine in aqueous solution,organic solvent and air

Water-soluble pillar[5]arenes are a class of typical macrocycles and have aroused tremendous attention for its easy to modify, abundant host-guest properties and extensive applications. However, up to now, all the reported water-soluble pillar[5]arenes acted as the host molecules, whereas they failed to be postsynthetically modified, which seriously impeded the development of the pillar[5]arene-based supramolecular chemistry. In this work, a new water-soluble pillar[5]arene, pillar[4]arene[1]quinone, was designed and synthsized with eight quaternary ammonium groups as well as a quinone units. Such a new water-soluble pillar[4]arene[1]quinone was capable of forming 1:1 stable complex with sodium 1-octanesulfonate in aqueous solution. Since the 1,4-quinone unit of WP[4]Q[1] could react with ethylenediamine (EDA) to form a conjugated quinoxaline structure, so pillar[4]arene[1]quinone could apply to the facile fluorescence turn-on sensing of EDA in aqueous solution, organic solvent and air.     

P=C bonds as building blocks for three- and four-membered heterocyclic cations: synthesis, structures and mechanistic studies

The activation of the P=C bond of phosphaalkenes with electrophiles is investigated as a means to prepare and characterize unusual organophosphorus compounds. Treatment of RP=CHtBu (1a: R=tBu; 1b: R=1-adamantyl) with HOTf (0.5 equiv) affords diphosphiranium salts [RP-CHtBu-PR (CH(2)tBu)]OTf ([2a]OTf and [2b]OTf), each containing a three-membered P(2)C ring. In contrast, the addition of MeOTf (0.5 equiv) to either 1a or 1b affords diphosphetanium salts [RP-CHtBu-P(Me)R-CHtBu]OTf ([3a]OTf and [3b]OTf) containing four-membered P(2)C(2) heterocycles. The phosphenium triflate [tBuP(CH(2)tBu)]OTf ([5a]OTf) and methylenephosphonium triflate [tBu(Me)P=CHtBu]OTf ([7a]OTf) are identified spectroscopically as intermediates in the formation of [2a](+) and [3a](+), respectively. The phosphenium triflate intermediate can be trapped with 2-butyne to afford phosphirenium salt [MeC=CMe-tBuPCH(2)tBu]OTf ([6a]OTf). Treatment of diphosphetanium [3a]OTf with an excess MeOTf affords [Me(2)P-CHtBu-PMetBu-CHtBu](OTf)(2) ([4a](OTf)(2)), a compound containing a diphosphetanium dication. The molecular structures are reported for [2a]OTf, [2b][H(OTf)(2)], [3a]I, [3b]I, [4a](OTf)(2), and [6a]OTf.     

Synthesis and cytotoxic activity of benzo[a]pyrano[3,2-h] and [2,3-i]xanthone analogues of psorospermine, acronycine, and benzo[a]acronycine

Condensation of 2-hydroxy-1-naphthalenecarboxylic acid with phloroglucinol afforded 9,11-dihydroxy-12H-benzo[a]xanthen-12-one (6). Construction of an additional dimethylpyran ring onto this skeleton, by alkylation with 3-chloro-3-methyl-1-butyne followed by Claisen rearrangement, gave access to 6-hydroxy-3,3-dimethyl-3H,7H-benzo[a]pyrano[3,2-h]xanthen-7-one (12) and 5-hydroxy-2,2-dimethyl-2H,6H-benzo[a]pyrano[2,3-i]xanthen-6-one (13), which were methylated into 6-methoxy-3,3-dimethyl-3H,7H-benzo[a]pyrano[3,2-h]xanthen-7-one (14) and 5-methoxy-2,2-dimethyl-2H,6H-benzo[a]pyrano[2,3-i]xanthen-6-one (15), respectively. Osmium tetroxide oxidation of 14 and 15 gave the corresponding (+/-)-cis-diols 16 and 17, which afforded the corresponding esters 18-21 upon acylation. Similarly, condensation of 2-hydroxy-1-naphthalenecarboxylic acid with 3,5-dimethoxyaniline gave 11-amino-9-methoxy-12H-benzo[a]xanthen-12-one (23) which was converted into 11-amino-9-hydroxy-12H-benzo[a]xanthen-12-one (24) upon treatment with hydrogen bromide in acetic acid. Alkylation with 3-chloro-3-methyl-1-butyne followed by Claisen rearrangement afforded 6-amino-3,3-dimethyl-3H,7H-benzo[a]pyrano[3,2-h]xanthen-7-one (25) and 5-amino-2,2-dimethyl-2H,6H-benzo[a]pyrano[2,3-i]xanthen-6-one (26). The new benzopyranoxanthone derivatives only displayed marginal antiproliferative activity when tested against L1210 and KB-3-1 cell lines. The only compounds found significantly active against L1210 cell line, 16 and 20, belong to the benzo[a]pyrano[3,2-h]xanthen-7-one series, which possess a pyran ring fused angularly onto the xanthone basic core.     

Synthesis and cytotoxicity of 9-(2-deoxy-2-alkyldithio-beta-D-arabinofuranosyl)purine nucleosides which are stable precursors to potential mechanistic probes of ribonucleotide reductases

A series of 2[prime or minute]-thionucleosides, as potential inhibitors of ribonucleotide reductases, has been synthesized. Treatment of the 3[prime or minute],5[prime or minute]-O-TPDS-2[prime or minute]-O-(trifluoromethanesulfonyl)adenosine with potassium thioacetate gave the arabino epimer of 2[prime or minute]-S-acetyl-2[prime or minute]-thioadenosine which was deacetylated to give 9-(3,5-O-TPDS-2-thio-[small beta]-d-arabinofuranosyl)adenine in high yield. Treatment of the latter with diethyl azodicarboxylate-C(3)H(7)SH-THF gave 2[prime or minute]-propyl disulfide which was desilylated to give 9-(2-deoxy-2-propyldithio-[small beta]-d-arabinofuranosyl)adenine. Subsequent tosylation (O5[prime or minute]) and displacement of the tosylate with pyrophosphate afforded the 5[prime or minute]-O-diphosphate in a stable form as propyl mixed-disulfide, which upon treatment with dithiothreitol releases 9-(2-thio-[small beta]-d-arabinofuranosyl)adenine 5[prime or minute]-diphosphate. The arabino 2[prime or minute]-mercapto group might interact with the crucial thiyl radical at cysteine 439 leading to the inhibition of ribonucleotide reductases via formation of a Cys439-2[prime or minute]-mercapto disulfide bridge. The 2,6-diamino-, 2-amino-6-chloro- and 2-amino-6-methoxypurine ribosides were also converted to the corresponding 2[prime or minute]-deoxy-2[prime or minute]-propyldithio-[small beta]-d-arabinofuranosyl nucleosides, which might serve as convenient precursors to the arabino epimer of 2[prime or minute]-thioguanosine. Analogously, 2[prime or minute]-deoxy-2[prime or minute]-propyldithioadenosine was prepared from 9-([small beta]-d-arabinofuranosyl)adenine. The nucleoside disulfides show modest cytotoxicity in a panel of human tumor cell lines.     

[7+2]- and [11+2]-cycloaddition reactions of diazo-azoles with isocyanates to azolo[5,1-d] [1,2,3,5] tetrazine-4-ones

Diazo-azoles react as 1,7- or 1,11-dipoles with isocyanates to form the hitherto unknown pyrazolo[5,1-d] [1,2,3,5]tetrazine-4-ones, [1,2,3,5]tetrazino[5,4-b]indazole-4-ones and [1,2,3]triazolo[5,1-d][1,2,3,5]tetrazine-4-ones in a [7+2]- or [11+2]-cycloaddition reaction.     

Helic[6]arene-Based Chiral Pseudo[1]rotaxanes and [1]Rotaxanes

Chiral pseudo[1]rotaxanes and [1]rotaxanes constructed from macrocyclic arenes still remain a big challenge mainly owing to the lack of such chiral macrocycles. In this work, a new system of chiral pseudo[1]rotaxanes formed by self-inclusion of helic[6]arene containing amide linked with the terminal tertiary amines was first discovered. Based on an atom-economic stopping strategy, a pair of chiral [1]rotaxanes were conveniently obtained in almost quantitative yields by blocking the pseudo[1]rotaxanes with monobenzyl bromide of tetraphenylethene. The structures of pseudo[1]rotaxanes and [1]rotaxanes were characterized by 2D NMR spectra in solution, combined with DFT calculations. The photophysical properties further revealed the efficient chirality transfer of helic[6]arene to the tetraphenylethene moiety, compared to their unthreaded chiral isomers. The discovery of the chiral pseudo[1]rotaxanes allows for a wide and available synthesis of chiral [1]rotaxanes, and also opening a new avenue to the design of chiral supramolecular materials.     

Influence of Amide Connectivity on the Hydrogen-Bond-Directed Self-Assembly of [n.n]Paracyclophanes

Reported here is the synthesis and self-assembly characterization of [n.n]paracyclophanes ( [n.n]pCps , n=2, 3) equipped with anilide hydrogen bonding units. These molecules differ from previous self-assembling [n.n]paracyclophanes ( [n.n]pCps ) in the connectivity of their amide hydrogen bonding units (C-centered/carboxamide vs. N-centered/anilide). This subtle change results in a ≈30-fold increase in the elongation constant for the [2.2]pCp -4,7,12,15-tetraanilide ( [2.2]pCpNTA ) compared to previously reported [2.2]pCp -4,7,12,15-tetracarboxamide ( [2.2]pCpTA ), and a ≈300-fold increase in the elongation constant for the [3.3]pCp -5,8,14,17-tetraanilide ( [3.3]pCpNTA ) compared to previously reported [3.3]pCp -5,8,14,17-tetracarboxamide ( [3.3]pCpTA ). The [n.n]pCpNTA monomers also represent the reversal of a previously reported trend in solution-phase assembly strength when comparing [2.2]pCpTA and [3.3]pCpTA monomers. The origins of the assembly differences are geometric changes in the association between [n.n]pCpNTA monomers—revealed by computations and X-ray crystallography—resulting in a more favorable slipped stacking of the intermolecular π-surfaces ( [n.n]pCpNTA vs. [n.n]pCpTA ), and a more complementary H-bonding geometry ( [3.3]pCpNTA vs. [2.2]pCpNTA ).     

Synthesis of porphyrin dimers fused with a benzene unit

Bicyclo[2.2.2]octadiene-connected pyrrolo-porphyrins have been prepared by an inverse-type [3+1] porphyrin synthesis of a bicyclo[2.2.2]octadiene-fused dipyrrole with a tripyrrane dicarbaldehyde. Another [3+1] porphyrin synthesis of pyrrole-connected porphyrins with the same or other tripyrrane dicarbaldehydes gave bicyclo[2.2.2]octadiene-bridged diporphyrins, the central metals and/or peripheral substituents of which were different. Thermal decomposition of the bicyclo[2.2.2]octadiene skeleton to a benzene moiety gave pi-system-fused porphyrin dimers in a highly pure form.     

Cyclocondensation of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyrid-2-ones with heterocyclic N,N-and N,C-1,3-dinucleophiles

[3+3] Cyclocondensation of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyrid-2-ones with heterocyclic N,N-and N,C-1,3-dinucleophiles proceeds regioselectively to give a series of new tri-and tetracyclic heterosystems, viz. derivatives of 5,6-dihydropyrazolo[1,5-a]pyrido[2,3-d]pyrimidin-6-one, 1,2-dihydropyrido[2,3-d]pyrido[2′,3′: 3,4]pyrazolo[1,5-a]pyrimidin-2-one, 8,9-dihydro-5H-pyrido-[2,3-d]thiazolo[3,2-a]pyrimidin-8-one, 1,2-dihydrobenzo[4,5]imidazo[1,2-a]pyrido[2,3-d]pyrimidin-2-one, and 1,2-dihydrobenzo[4,5]imidazo[1,2-g][1,6]naphthyridin-2-one.     

Investigations of the products of the reaction of epichlorohydrin with aromatic amines

Heating 3-hydroxy-1,2,3,4-tetrahydrobenzo[h]quinoline with phosphorus oxychloride gave a mixture of isomeric 3-chloro-1,2,3,4-tetrahydrobenzo[h]quinoline and 2-(chloromethyl)-benz[g]indoline, which are converted to a mixture of 3-benzoyloxy-1,2,3,4-tetrahydrobenzo-[h]quinoline and 2-(benzoyloxymethyl)benz[g]indoline on reaction with potassium benzoate. Saponification of 2-(benzoyloxymethyl)benz[g]indoline gave 2-(hydroxymethyl)benz[g]indoline. The reaction of the isomeric chloro derivatives with potassium cyanide gave 2-(benz[g]-indolinyl)acetonitrile.See [1] for communication IX.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 362–366, March, 1972.     

Binding modes of cucurbit[6]uril and cucurbit[7]uril with a series of bis-pyridinium compounds

Binding behaviors of cucurbit[6]uril (CB[6]) and cucurbit[7]uril (CB[7]) with a series of bis-pyridinium compounds N, N’-hexamethylenebis(1-alkyl-4-carbamoyl pyridinium bromide) (HBPB-n) (alkyl chain length, n = 6, 8 and 10) guests were investigated using ¹H-NMR, ESI–MS and single crystal X-ray diffraction methods. The results show that CB[6] and CB[7] can form [2]pseudorotaxanes with HBPB-n easily. When increasing the length of tail alkyl chain, the binding site of CB[6] at guest molecules changed from the tail to the middle part, while CB[7] remained located over the tail chain. As CB[6] and CB[7] were added in HBPB-8 aqueous solution, a [3]pseudorotaxane was formed by the inclusion of the internal middle site in CB[6] and the tail chain in CB[7].     

Synthesis and some properties of binuclear ruthenocenes bridged by oligoynes: formation of bis(cyclopentadienylidene)cumulene diruthenium complexes in the two-electron oxidation

The monoynes [Rc*C[triple bond]CRc*] and [Rc'C[triple bond]CRc'] were obtained in improved yields using [Mo(CO)6]/2-FC6H5OH as a catalyst in the alkyne metathesis of [Rc*C[triple bond]CMe] and [Rc'C[triple bond]CMe], respectively (Rc = ruthenocenyl, Rc* = 1',2',3',4',5'-pentamethylruthenocenyl, and Rc' = 2',3',4',5'-tetramethylruthenocenyl groups). The diynes [Rc*(C[triple bond]C)2Rc*] and [Rc'(C[triple bond]C)2Rc'] were synthesized by the oxidative coupling of the corresponding terminal ethynes in good yields. The triyne [Rc*(C[triple bond]C)3Rc*] and the tetrayne [Rc*(C[triple bond]C)4Rc*] were prepared by the hetero- and homocoupling of [Rc*C[triple bond]CC[triple bond]CH], which was obtained from the reaction of [Rc*C[triple bond]CCHO] with Li[N2CSiMe3], respectively. Although the oxidation waves did not always exhibit a clear two-electron oxidation process, the oxidation potentials shifted to a lower potential with an increase in the number of methyl substituents on the ruthenocenyl ring, and shifted to a higher potential with the increase in the number of C[triple bond]C units; this result is in contrast to that found in the [Rc(CH=CH)(n)Rc] series. The chemical oxidation of [Rc'C[triple bond]CRc'] yielded a stable two-electron-oxidized species, the structure of which was confirmed by X-ray crystallography to be [Ru2(mu2-eta(6):eta(6)-C5Me4C=CC5Me4)(eta-C5H5)2](BF4)2. Changing the substituents (Rc, Rc*, and Rc') had no effect on the chemical oxidation, but in the case of the Rc' series the Me substituent increased the stability of the two-electron-oxidized species in solution. The diyne [Rc*(C[triple bond]C)2Rc*] and the triyne [Rc*(C[triple bond]C)3Rc*] also gave a similar but unstable two-electron-oxidized species. In acetone or acetonitrile, the two-electron-oxidized species of [Rc*C[triple bond]CRc*] and [Rc*(C[triple bond]C)2Rc*] gradually formed the corresponding bis(fulvene)-type complexes. This implies that the two-electron-oxidized species of [Rc*(C[triple bond]C)(n)Rc*] are destabilized with the increasing n.     

Synthesis and characterization of novel Schiff bases containing pyrimidine unit

The work involves synthesis of novel Schiff base derivatives containing a pyrimidine unit starting with chalcones. 4-Aminoacetophenone was reacted with 4-nitrobenzaldehyde or 4-chlorobenzaldehyde in basic medium giving chalcones, [I]_a and [I]_b, respectively, by Claisen-Schemidt reaction. The chalcones [I]_a and [I]_b were reacted with urea in HCl medium giving oxopyrimidines, [II]_a and [II]_b. They were also reacted with thiourea in basic medium to give thioxopyrimidines, [III]_a and [III]_b. The novel mono and bis Schiff bases, [VIII]_na, [VIII]_nb, [IX]_na, [IX]_nb, [X]_na, [X]_nb, [XI]_na, and [XI]_nb were synthesized by the reaction of pyrimidine derivatives; oxopyrimdines, [II]_a and [II]_b and thioxopyrimidines, [III]_a and [III]_b with 4-(4′-n-alkoxybenzoloxy)benzaldehyde [VI] and polymethylene-α,ω-bis-4-oxybenzaldehydes [VII]_m, respectively, in dry benzene using drops of glacial acetic acid as a catalyst. The synthesized compounds were characterized by melting points, elemental analysis, FTIR, and ¹H NMR spectroscopy.     

Part 1: Synthesis of Polyfused Heterocyclic Systems Derived From 3-Phenyl-5,6,7,8-tetrahydro[1,2,4]triazolo[3,4- b ][1,3,4]thiadiazepine-6,8-dione

3-Phenyl-5,6,7,8-tetrahydro[1,2,4]triazolo[3,4- b ][1,3,4]thiadiazepine-6,8-dione ( 1 ) was condensed with o -aminothiophenol, 2-amino-ethanol or cystamine to afford compounds 2-4 respectively. Treatment of compound 1 with dimethylthiomethylenemalononitrile yielded the corresponding pyrano[3,2- f ][1,2,4]triazolo[3,4- b ]-[1,3,4]thiadiazepine derivative 5 . 7-[5-Amino-1,3-dithiolan-2-ylidene]-3-phenyl-5,6,7,8-tetrahydro[1,2,4]triazolo[3,4- b ][1,3,4]thiadiazepine-6,8-dione ( 6 ) was obtained by treating compound 1 with CS 2 and chloroacetonitrile. Thiation of compound 1 gave the corresponding thioanalog 7 , which in turn was condensed with malononitrile to give 3-phenyl-5,6,7,8-tetrahydro[1,2,4]triazolo[3,4- b ][1,3,4]thiadiazepine-6-one-8-ylidenemalononitrile ( 8 ). On treating compound 8 with benzaldehyde or p -nitrobenzaldehyde, pyrano[1,2,4]triazolo[1,3,4]thiadiazepin derivatives 9a , b , respectively, were obtained. Compound 8 was treated with CS 2 and methyl iodid to give the corresponding dithiomethylmethylene derivative 10 which was subjected to react with aniline to give pyrido[1,2,4]triazolo[1,3,4]thiadiazepine derivative 11 . Compound 8 was treated with 3-aminopyridine, o -aminothiophenol, or o -phenylenediamene to yield compounds 12 and 13a , b respectively. Finally, tertiary amines or activated phenols were condensed with compound 8 to yield compounds 14 and 15a , b respectively.     

Binding modes of cucurbit[6]uril and cucurbit[7]uril with a tetracationic bis(viologen) guest

Binding behaviors of two cucurbit[n]urils (CB[n]) hosts with the [CH3bpy(CH2)6bpyCH3]4+ (bpy = 4,4'-bipyridinium) guest were investigated by 1H NMR and MALDI-TOF-MS experiments. While the CB[6] and CB[7] form [2]pseudorotaxanes with the host located over the hexamethylene chain of the guest, only the CB[7] forms a [3]pseudorotaxane with both host molecules residing over the bipyridinium groups. The initial CB[7] host vacates the inclusion of the hexamethylene chain as a result of the electrostatic and steric repulsions that would arise in simultaneous binding of adjacent aliphatic and aromatic portions of the guest.     

Synthesis and structure of upper-rim 1,3-alternate tetraoxacalix[2]arene[2]triazine azacrowns and change of cavity in response to fluoride anion

The upper-rim 1,3-alternate tetraoxacalix[2]arene[2]triazine azacrowns were constructed effectively by macrocyclic condensation reaction of diamines with dichlorinated tetraoxacalix[2]arene[2]triazine intermediates that were synthesized from the stepwise fragment coupling reactions of 3,5-dihydroxybenzoic acid esters with cyanuric chlorides. Because of the formation of conjugation of amino groups with triazine rings, tetraoxacalix[2]arene[2]triazine azacrowns existed in a mixture of syn- and anti-isomeric forms. Both fluorescence titration and 1H NMR spectroscopic study showed that tetraoxacalix[2]arene[2]triazine azacrowns interacted with fluoride anion, leading to cavity changes of the host molecules.