Encapsulation of a (H3O2)- unit in the aromatic core of a calix[6]arene closed by two Zn(II) ions at the small and large rims

The coordination of a first Zn(II) ion to a calix[6]arene presenting three imidazolyl arms at the small rim and three aniline moieties at the large rim allows the binding of a second Zn(II) ion while hosting a (H3O2)- unit in the aromatic cavity.     

Tris(triazolyl) calix[6]arene-based zinc and copper funnel complexes: imidazole-like or pyridine-like? A comparative study

Huisgen dipolar cycloaddition leads straightforwardly to new funnel complexes based on the calix[6]arene macrocycle bearing three functionalized triazoles as coordinating units at the small rim. Coordination to Zn(II) and Cu(I) cations was studied using (1)H NMR and IR spectroscopies and cyclic voltammetry. The nature of the substituents on the triazole ring affects the behavior of the ligands and their coordinating ability and controls the host-guest properties of the metal receptors for exogenous substrates. Depending on their substitution pattern but also on the metal ion and the guest ligand, the triazole-based systems behave either imidazole-like or pyridine-like. The ease of preparation and the versatility of 1,4-disubstituted-1,2,3-triazoles with tunable steric and electronic properties make them promising candidates for further applications from biology to materials.     

Di- and trinuclear Zn2+ complexes of calix[4]arene based ligands as catalysts of acyl and phosphoryl transfer reactions

The calix[4]arene scaffold, blocked in the cone conformation by proper alkylation of the lower rim hydroxyls, was used as a convenient molecular platform for the design of bi- and trimetallic Zn2+ catalysts. The catalytic activity of the Zn2+ complexes of calix[4]arenes decorated at the 1,2-, 1,3-, and 1,2,3-positions of the upper rim with 2,6-bis[(dimethylamino)methyl]pyridine units were investigated in the cleavage of ester 6 and of the RNA model compound HPNP. High rate enhancements, up to 4 orders of magnitude, were observed in a number of catalyst-substrate combinations. Interestingly the order of catalytic efficiency among regioisomeric dinuclear complexes in the cleavage of ester 6 is 1,2-vicinal > 1,3-distal, but it is reversed in the reaction of HPNP. The higher efficiency of trinuclear compared to dinuclear complexes provides an indication of the cooperation of three Zn2+ ions in the catalytic mechanism.     

Supramolecular control of hetero-multinuclear polytopic binding of metal ions (Zn(II), Cu(I)) at a single calix[6]arene-based scaffold

A Calix[6]arene scaffold was functionalized to provide a tridentate binding site at the small rim and three bidentate chelate sites at the large rim of the cone to generate a heteropolytopic ligand. Its complexation to one equivalent of Zn(II) at the small rim yields a funnel complex displaying both host-guest properties and preorganization of the three chelate groups at the large rim. These two aspects allowed the full control of the binding events to regioselectively form dinuclear Zn(II) and heteropolynuclear Zn(II)/Cu(I) complexes. The heteropolynuclear systems all rely on the host-guest relationship thanks to the induced-fit behavior of the calix cavity. With the short guest MeCN, the large rim is preorganized into a trigonal tris-triazole core and accommodates a single Cu(I) ion. A long guest breaks this spatial arrangement, and three Cu(I) ions can then be bound at the tris-bidentate triazole-dimethylamine site at the large rim. In a noncoordinating solvent however, the tetranuclear complex is submitted to scrambling and the addition of exogenous π-acceptor ligands is required to control the binding of Cu(I) in a well-defined environment. Hindrance selectivity was then induced by the accessibility at the small rim site. Indeed, while CO can stabilize Cu(I) at both coordination sites, PPh(3) cannot fit into the cavity and forces Cu(I) to relocate at the large rim. The resulting well-defined symmetrical tetranuclear complex thus arises from the quite remarkable selective supramolecular assembly of nine partners (1 Zn(II), 3 Cu(I), 1 calixarene, 1 guest alkylamine, 3 PPh(3)).     

X-ray crystal structure of a p-hydroxycalix[6]arene derivative

The first molecular structure of a p-hydroxycalix[6]arene 6 has been determined by a single crystal X-ray diffraction study. The calix[6]arene molecule assumes a 1,2,3-alternate conformation with all OH groups at the upper rim engaged in H-bonds with pyridine molecules. The stacking of molecules of p-hydroxycalix[6]arene 6 along the a and c axes gives rise to a solvent pseudo-cylindrical cavity at the centre of the cell.     

Innovative methodologies for the N-protection of N-alkylimidazole groups: application to the first synthesis of a water-soluble calix[6]arene presenting three ammonium substituents at the large rim and three neutral N-donors at the small rim

The first synthesis of a cationic amphiphile calixarene ligand, which bears three neutral imidazole donors on one side of the hydrophobic cone and three quaternary ammonium substituents on the other side, is reported. The synthetic strategy relies on two key steps: (i) the "small rim-directed" selective ipso-nitration at the large rim and (ii) a protection-deprotection sequence of the N-alkylimidazole groups, for which two equally efficient novel methods (coordination to Zn(II) or to a cyanoborane) are presented.     

Spectacular induced-fit process for guest binding by a calix[6]arene Zn(II) funnel complex

The host properties of a calix[6]arene cone capped by a Zn(II) tris-imidazole core at the small rim and decorated by three NH(2) substituents at the large rim are described and compared to the hexa-tBu parent complex. It is shown that the replacement of three bulky tBu substituents by three hydrophilic and small NH(2) groups has three major impacts: the receptor is now soluble in aqueous media, it accepts large guests such as dimethyldopamine and, most interestingly, undergoes a spectacular induced-fit behavior for guest binding.     

Fixed or invertible calixarene-based directional shuttles

The first examples of rotaxanes based on calixarenes threaded by dialkylammonium ions, which also represent the first examples of calixarene-based molecular shuttles, are reported. The base/acid treatment demonstrated that these systems act as molecular shuttles, which move between three sites on the axle. When small OMe groups are appended at the calix[6]arene lower rim an unprecedented inversion of its shuttling direction is observed, which occurs through a cone-to-cone inversion of the macrocycle.     

Selective hetero-trisfunctionalization of the large rim of a biomimetic calix[6]arene using host-guest chemistry as a synthetic tool

A calix[6]arene has been selectively functionalized by three different groups at the large rim. The strategy relies on the hostguest recognition chemistry of a biomimetic metal complex at the small rim (so-called "funnel complex") and the Huisgen cycloaddition. The intramolecular thermal reaction proceeds with a high efficiency, chemio- and regioselectivity, allowing the monofunctionalization of one aromatic unit among three. Thanks to the high yield and selectivity of the reaction, it can be applied successively twice on the same compound, which opens the route for inherently chiral calix[6]arenes. This methodology not only is of wide potential for obtaining and exploiting calix[6]arenes that are dissymmetrized at the large rim, but also stands as an exemplary strategy for the selective appending of a functional group on a host platform.     

The reaction of fullerene C(60) with 4,6-dimethyl-1,2,3-triazine: formation of an open-cage fullerene derivative.

A thermal reaction of fullerene C(60) with 4,6-dimethyl-1,2,3-triazine (4) in o-dichlorobenzene gave azacyclohexadiene-fused fullerene derivative 5, by the reaction with intermediate azete 11, and then, after flash chromatography over SiO(2), open-cage fullerene derivative 6 having an eight-membered ring orifice on the C(60) cage. Compound 6 is assumed to be formed via addition of diradical intermediate 13 to C(60). Compound 6 underwent a further photochemical reaction with singlet oxygen with the cleavage of one of the double bonds at the rim of the orifice to afford triketone derivative 8 having a 12-membered ring orifice.     

1,2,3-三氮杂苯－(水)3复合物多体相互作用

The interaction between 1,2,3-triazine and three water molecules was studied using density functional theory B3LYP method at 6-31-t＋＋G^＊＊ basis set. Various structures for 1,2,3-triazine-（water）n （n= 1, 2, 3） complex were investigated and the different lower energy structures were reported. Many-body analysis was also carded out to obtain relaxation energy and many-body interaction energy （two, three, and four-body）, and the most stable conformer has the basis set superposition error corrected interaction energy of -- 102.61 kJ/mol. The relaxation energy, two- and three-body interactions have significant contribution to the total interaction energy whereas four-body interaction was very small for 1,2,3-triazine-（water）3 complex.     

Ipso-Nitration of calix[6]azacryptands: intriguing effect of the small rim capping pattern on the large rim substitution selectivity

The ipso-nitration of calix[6]arene-based molecular receptors is a important synthetic pathway for the elaboration of more sophisticated systems. This reaction has been studied for a variety of capped calixarenes, and a general trend for the regioselective nitration of three aromatic units out of six in moderate to high yield has been observed. This selectivity is, in part, attributed to the electronic connection between the protonated cap at the small rim and the reactive sites at the large rim. In addition, this work highlights the fact that subtle conformational properties can drastically influence the outcome of this reaction.     

Synthesis and binding studies of novel diethynyl-pyridine amides with genomic promoter DNA G-quadruplexes

Herein, we report the design, synthesis and biophysical evaluation of novel 1,2,3-triazole-linked diethynyl-pyridine amides and trisubstituted diethynyl-pyridine amides as promising G-quadruplex binding ligands. We have used a Cu(I)-catalysed azide-alkyne cycloaddition click reaction to prepare the 1,2,3-triazole-linked diethynyl-pyridine amides. The G-quadruplex DNA binding properties of the ligands have been examined by using a F?rster resonance energy transfer (FRET) melting assay and surface plasmon resonance (SPR) experiments. The investigated compounds are conformationally flexible, having free rotation around the triple bond, and exhibit enhanced G-quadruplex binding stabilisation and specificity between intramolecular promoter G-quadruplex DNA motifs compared to the first generation of diaryl-ethynyl amides (J. Am. Chem. Soc. 2008, 130, 15950-15956). The ligands show versatility in molecular recognition and promising G-quadruplex discrimination with 2-50-fold selectivity exhibited between different intramolecular promoter G-quadruplexes. Circular dichroism (CD) spectroscopic analysis suggested that at higher concentration these ligands disrupt the c-kit2 G-quadruplex structure. The studies validate the design concept of the 1,3-diethynyl-pyridine-based scaffold and demonstrate that these ligands exhibit not only significant selectivity over duplex DNA but also variation in G-quadruplex interaction properties based on small chemical changes in the scaffold, leading to unprecedented differential recognition of different DNA G-quadruplex sequences.     

Photo- and thermal elimination of nitrogen from 4-phenyl- and 4,5-diphenyl-1,2,3-triazole

Phenylacetonitrile ( 2 ) (32%) and small amounts of benzyl methyl ether ( 3 ), benzonitrile ( 5 ) and methyl benzoate ( 6 ) were produced by irradiation of either 4-phenyl-1,2,3-triazole ( 1 ) or 4-phenyl-5-deutero-1,2,3-triazole ( 7 ) in methanol at 254 nm. In methylene chloride, irradiation of 1 produced 2 (15%) and small amounts of 3,6-diphenyl-1,2,4,5-tetrazine ( 8 ). Irradiation of 4,5-diphenyl-1,2,3-triazole ( 9 ) in methanol gave 2,4,5-triphenylimidazole ( 11 ) (4%) and trace amounts of diphenylacetonitrile ( 10 ), benzamide ( 12 ), and compounds 3 , 5 , and 6 . Irradiation of 2,3-diphenyl-2H-azirine ( 13 ) in methanol gave small amounts of 3 , benzaldehyde ( 4 ), and compounds 5 , 6 , 12 as well as 2,3,5,6-tetraphenylpyrazine ( 14 ) and in methylene chloride it gave 11 (16%) and small amounts of 4 , 5 , 14 , and acetophenone ( 15 ). On heating 4-phenyl-1,2,3-triazole ( 1 ) in n-hexadecane, elimination of nitrogen at 290° left phenylacetonitrile ( 2 ) as the only identified product. Similar pyrolysis of 4,5-diphenyl-1,2,3-triazole ( 9 ) produced 2,3,5,6-tetraphenylpyrazine ( 14 ) along with an intractable material. An efficient thermal isomerization of 2,3-diphenyl-2H-azirine ( 13 ) gave 2-phenylindole ( 17 ).     

Binding ability of Zn-tetraarylporphyrins with two,four and eight 4-(4-(3,6-bis(t-butyl)carbazol-9-ylphenyl)-1,2,3-triazole end groups towards N-containing substrates of different nature

The binding ability of Zn-tetraarylporphyrins with two, four and eight 4-carbazolylphenyl-1,2,3-triazole end groups towards 1,4-diazabicyclo[2.2.2]octane, pyridine and 1,2,3-triazole in toluene was studied by spectrophotometric and ¹H NMR titration. It was determined that due to a good geometric match of the ligand size to the size of the intramolecular cavities of the porphyrinic receptor, and by the existence of additional π–π and/or hydrogen bonding interactions between the ligand and the triazole fragments of the porphyrin, the Zn-tetraarylporphyrin with eight 4-carbazolylphenyl-1,2,3-triazole end groups could be used as an effective receptor for 1,2,3-triazole and other small heterocycles such as pyridine. Taking into account the fact that binding is accompanied by a clear and easily identifiable response in the UV–vis spectra of the reaction mixture, this metalloporphyrin could be considered as a molecular optical sensing device for small heterocyclic substrates.     

Selective synthesis of 1,3-dialkyl-4-nitro-1,2,3-triazolium salts from 1-alkyl-4-nitro-1,2,3-triazoles and dialkyl sulfates

The process of alkylation of 1-alkyl-substituted 4-nitro-1,2,3-triazoles with dimethyl and diethyl sulfates has been studied. The structures of the N,N’-dialkyl-C-nitro-1,2,3-triazolium alkylsulfates and perchlorates has been confirmed by IR, ¹H and ¹³C NMR spectroscopy. Alkylation with an excess of dialkyl sulfate occurred regioselectively at N-3 with the formation of 1,3-dialkyl-4-nitro-1,2,3-triazolium salts, which is in agreement quantum-chemical calculations of the relative stability of the corresponding isomeric cations. The molecular and crystal structures of the first example of this type of salt – 1,3-diethyl-4-nitro-1,2,3-triazolium perchlorate – have been determined by X-ray crystallo-graphy. Nitrotriazolium salts with mixed alkyl substituents – 3-ethyl-1-methyl- and 1-ethyl-3-methyl-4-nitro-1,2,3-triazolium salts – have been synthesized an studied for the first time.     

Synthesis, Structure and Selective Upper Rim Functionalization of Long Chained Alkoxythiacalix[4]arenes

The synthesis and X-ray structure investigation of the cone shaped monodecyloxythiacalix[4]arene, as well as the introduction of the reactive bromide or chloromethyl groups on it’s upper rim are described. Preparation of the amphiphilic derivative of thiacalixarene bearing three hydrophilic diethoxyphosphoryl groups at the upper rim and lipophilic decyloxy group at the lower rim is presented.     

[3+2]‐Cycloaddition for Fully Decorated Vinyl‐1,2,3‐Triazoles: Design,Synthesis and Applications

The s mall heterocyclic ring of the 1,2,3‐triazole module is one of the most widely investigated compounds in numerous applications of biological, medicinal, pharmaceutical and materially important molecules. In this regard, a large number of synthetic methodologies and approaches have already been reported to construct such a heterocyclic core structure in a selective manner. However, the vinyl‐substituted 1,2,3‐triazole moiety is another privileged segment in heterocyclic chemistry. The selective introduction of simple vinyl and functionalized vinyl groups onto the three different positions of the 1,2,3‐triazole framework can significantly improve the properties of the molecule. Accordingly, high‐yielding efficient approaches for the selective construction of vinyl‐containing 1,2,3‐triazoles becomes a promising branch of chemistry among practitioners of industry and academia. In this minireview, we have discussed recent advances in the construction of highly selective three different vinyl‐containing 1,2,3‐triazoles. In addition, representative synthetic methodologies and approaches for the corresponding three different classes of vinyl‐1,2,3‐triazoles and their applications have been described as well in this review.     

Cu(I)‐Catalyzed Regioselective and Highly Efficient One‐Pot Synthesis of Novel 1,2,3‐Triazoles Decorated with Pyridine and Heterocyclic Amines

An efficient one‐pot synthesis of 1,2,3‐triazoles via the three‐component coupling reaction between propargyl bromide, secondary amines, and 3‐azidopyridine in the presence of CuI as catalyst has been presented. The reaction is highly regioselective and afforded novel 1,4‐disubstituted‐1,2,3‐triazoles in excellent yields by the [3 + 2] Huisgen cycloaddition reaction. This method avoids isolation and handling of terminal acetylenes. The ease of purification has made this methodology clean and safe for the synthesis of 1,2,3‐triazoles with a broad scope.     

Synthesis of "two-story" calix[6]aza-cryptands

The first four members of a new family of C(3v)-symmetrical "two-story" calix[6]aza-cryptands have been synthesized. These large funnel shaped aza-ligands are formed through introduction of three aromatic arms as spacers onto the small rim of a calix[6]arene and subsequently capped with the tripodal aza caps tacn [1,3,5-triazacyclononane] or tren [tris(aminoethyl)amine]. A key feature for an efficient final 1:1 macrocyclization appears to be an adequate geometrical fit between the extended calixarene scaffold and the aza caps.