N-Tosylpyrrolidine calix[4]pyrrole: synthesis and ion binding studies

The synthesis and preliminary solution phase ion binding properties of the N-tosylpyrrolidine calix[4]pyrrole 2 are reported. This β-octaalkyl-substituted calix[4]pyrrole, the first to be prepared via a direct condensation reaction, was obtained by reacting the 3,4-alkyl-functionalized pyrrole 8 with acetone in the presence of an acid catalyst. On the basis of (1)H NMR spectroscopic analyses and isothermal titration calorimetry, it was concluded that, compared with the parent, β-unsubstituted calix[4]pyrrole (1), compound 2 possesses significantly enhanced binding ability for halide anions in chloroform. Furthermore, 2 proved capable of solubilizing in chloroform solution the otherwise insoluble salts, CsF and CsCl. These effects are ascribed to the interactions between the four tosyl groups present in 2 and the counter cations of the halide anion salts.     

Cyclo[2]carbazole[2]pyrrole: a preorganized calix[4]pyrrole analogue

A cyclo[2]carbazole[2]pyrrole (2) consisting of two carbazoles and two pyrroles has been synthesized by directly linking the carbazole 1- and 8-carbon atoms to the pyrrole α-carbon atoms. Macrocycle 2 is an extensively conjugated 16-membered macrocyclic ring that is fixed in a pseudo-1,3-alternate conformation. This provides a preorganized anion binding site consisting of two pyrrole subunits. ¹H NMR spectroscopic analysis revealed that only the two diagonally opposed pyrrole NH protons, as opposed to the carbazole protons, take part in anion binding. Nevertheless, cyclo[2]carbazole[2]pyrrole 2 binds representative anions with higher affinity in CD₂Cl₂ than calix[4]pyrrole (1), a well-studied non-conjugated tetrapyrrole macrocycle that binds anions via four pyrrolic NH hydrogen bond interactions. On the basis of computational studies, the higher chloride anion affinity of receptor 2 relative to 1 is rationalized in terms of a larger binding energy and a lower host strain energy associated with anion complexation. In the presence of excess fluoride or bicarbonate anions, compound 2 loses two pyrrolic NH protons to produce a stable dianionic macrocycle [2–2H]²⁻ displaying a quenched fluorescence.

Less is more: two NH hydrogen bond donors in a preorganized receptor provide greater anion affinity than the four NH moieties present in the classic anion receptor, calix[4]pyrrole.     

Practical synthesis and Diels-Alder chemistry of [4]dendralene

Spectacular new atom efficient domino cycloaddition sequences involving [4]dendralene, the simplest cross-conjugated tetraene, are reported. Up to eight stereocenters, three new rings, and six C-C bonds are generated in one synthetic operation. The site selectivity of dienophile addition to cross-conjugated trienes and tetraenes is controlled with a simple Lewis acid.     

Electrochemical synthesis of cyclo[8]pyrrole

The utility of an electrochemical oxidative strategy in the synthesis of expanded porphyrins is demonstrated by the preparation of cyclo[8]pyrrole in high yield via a bipyrrole C(2)-C(2)' coupling process.     

Siloxane-functionalized calix[4]pyrrole: synthesis, characterization and modification of silica-based solid supports

A siloxane-functionalized calix[4]pyrrole derivative was synthesized starting from the corresponding alcohol-functionalized calix[4]pyrrole. Structural elucidation was carried out by using NMR spectroscopy, mass spectrometry and X-ray diffraction analysis. The use of this siloxane-functionalized calix[4]pyrrole for modification of various silica solid supports (silica gel 60, fume silica, and SiO₂ nanopowder) was studied. Characterization of the modified silica solid supports was achieved by FTIR, TGA, and elemental analysis. It was also shown that the production of silica nanoparticles is possible via a sol-gel reaction of siloxane-functionalized calix[4]pyrrole and tetraethoxysilane (TEOS). Calix[4]pyrrole modified silica solid supports were found to sense chloride anions of Azure A dye.     

Calix[4]pyrrole Schiff base macrocycles. Novel binucleating ligands for mu-oxo iron complexes

New bimetallic mu-oxo diferric complexes of several previously reported calix[4]pyrrole Schiff base macrocycles are described. The synthesis of a new member of this class of macrocycles is also reported; it was prepared via an acid-catalyzed condensation between 1,9-bisformyl-5,5-dipropyldipyrromethane and o-phenylenediamine. Reactions of the free base macrocycles or their bis-HCl salts with Fe(II) mesitylene, followed by air oxidation, gave the binuclear mu-oxo bis-Fe(III) compounds 6-10 in moderate yield. X-ray crystallography data reveal two different coordination environments for the Fe-O-Fe subunit in 6-10 that it is suggested can be controlled by altering the reaction conditions. Structural properties of these metalated pyrrolic macrocycles are also compared to those of mu-oxo diferric porphyrins and mu-oxo diferric texaphyrin. Complexes 6-10 exhibit two distinct types of M-N bonds that are similar in length to the bonds observed in metallotexaphyrin complexes. However, the electronics of the present systems are very different from those of texaphyrins and porphyrins in that no delocalized bonding patterns are observed within the ligands as a whole.     

Azocalix[4]arene Strapped Calix[4]pyrrole: A Confirmable Fluoride Sensor

A new chromogenic fluoride sensor based on 1,3-di-p-nitrophenylazocalix[4]arene-calix[4]pyrrole (1) was designed and synthesized. The color of the solution of probe 1 changed upon the addition of any F(-), CH(3)CO(2)(-), PhCO(2)(-), and H(2)PO(4)(-) ions. However, from these ions the highly specific sensing of F(-) is achieved by the addition of Ca(2+) which leads to a color change from light sky blue (of 1·F(-)) back to the original light orange color of 1.     

Polymethine dyes based on cyclohepta[c]pyrrole

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1432–1433, October, 1991.     

A novel colorimetric and fluorometric anion sensor based on BODIPY-calix[4]pyrrole conjugate

A novel fluorescent anion sensor 1 based on boradiazaindacenes (BODIPY) derivative was synthesized and its absorption and fluorescence properties were investigated in various solvents. 1 exhibited a red shift of absorption spectrum and fluorescence quenching in varying degree in the presence of F^?, AcO^?, H₂PO₄ ^? and Cl^? due to multiple hydrogen bonding interactions between these anions and calix[4]pyrrole receptor. As an anion sensor in the visible region, 1 displayed the similar selectivity and sensitivity toward anions compared to the parent calix[4]pyrrole. However, 1 can be used as an effective dual responsive optical sensor for F^? via chromogenical and fluorogenical signals.     

New redox anion receptors based on calix[4]pyrrole bearing ferrocene amide

Two redox anion receptors based on calix[4]pyrrole and ferrocene have been synthesized. The electrochemical investigation revealed that these compounds can be response to the anions with different shifts of Fc/Fc⁺ couple. With the ¹H NMR titration study, the selectivity to F⁻ and AcO⁻ ions in CD₃CN solution was confirmed. The conformations of the mono-aromatic meso-substituted calix[4]pyrroles, which were the synthetical intermediate of the ferrocene based receptors, and their anion complexes in the solid state have also been studied by single X-ray crystallography, and the rationality of the crystal conformations was proved by theoretical study.     

Self-assembly of dimeric tetrathiafulvalene-calix[4]pyrrole: receptor for 1,3,5-trinitrobenzene

The synthesis and binding properties of a tetrathiafulvalene (TTF)-calix[4]pyrrole receptor 2 appended with one 3,5-dinitrobenzoate guest moiety are reported. The preliminary studies revealed that the receptor is self-complexing into a dimer receptor 2?2. The self-complexation of the receptor leads to preorganization--in its 1,3-alternate conformation--and as a result hereof, the dimer receptor 2?2 is displaying a 2 order higher binding affinity toward analytes (e.g., 1,3,5-trinitrobenzene) than the model tetrathiafulvalene (TTF)-calix[4]pyrrole receptor 3.     

Crown-6-calix[4]arene-capped calix[4]pyrrole: an ion-pair receptor for solvent-separated CsF ions

An ion-pair receptor, 1, containing both cation- and anion-recognizing sites, has been synthesized and characterized. Single-crystal X-ray diffraction structural studies and (1)H NMR spectroscopic analyses confirmed that 1 forms stable 1:1 complexes with CsF in solution and in the solid state in spite of the large separation enforced between the receptor-bound anion and cation. In 9:1 CDCl3/CD3OD, binding of fluoride anion within the calix[4]pyrrole core of 1 was not observed in the absence of a cobound cesium cation; however, it was seen in this solvent mixture under conditions where a Cs(+) cation was bound to the crown ether-strapped calix[4]arene subunit.     

Electrochemical synthesis of a thiophene-containing cyclo[9]pyrrole

A new member of the cyclo[n]pyrrole class of expanded porphyrins could be prepared from the corresponding thiophene-containing terpyrrole precursor through use of a mild electrochemical oxidative procedure. The isolated macrocycle, featuring nine heterocyclic subunits directly connected through their α,α'-positions, is the largest cyclo[n]pyrrole derivative reported to date (see figure).     

杯[4]吡咯大环化合物的合成和性能

通过改进的吡咯与酮缩合反应制备了一系列杯[4]吡咯大环主体分子,并由元素分析、IR、^1H NMR,MS确证结构。作为一类新型的阴离子和中性分子的受体,其性能通过光谱滴定实验进行了初步研究。     

Synthesis of cyclophane-like porphyrin-calix[4]pyrrole conjugates

New cyclophane-like porphyrin-calix[4]pyrrole conjugates were synthesized on the basis of meso-ethynyloctaethylporphyrin, and their physicochemical properties were studied.     

Calix[4]pyrrole[2]carbazole: a new kind of expanded calixpyrrole

The synthesis and anion binding properties of a new class of calixpyrrole analogue, containing two carbazole subunits in lieu of two of the four acetone bridging elements normally found in calix[4]pyrrole, is described. The compound exists in a winglike structure in the solid state, as judged from single-crystal X-ray diffraction analyses of both the free system and the corresponding benzoate anion complex. Evidence for anion binding in dichloromethane solution was obtained from static fluorescent quenching experiments; these latter revealed a slight preference for acetate relative to other carboxylate anions (e.g., benzoate, oxalate, succinate), as well as various other anionic substrates (i.e., chloride and dihydrogen phosphate). No evidence of binding was observed in the case of bromide, nitrate, and hydrogen sulfate.