Synthesis of nitro and amino derivatives of benzothiacrown ethers

The condensation reaction of 1,2-bis(2-haloethoxy)-4-nitrobenzenes with acyclic α,ω-(oxa)alkanedithiols in the presence of alkali metal carbonates produced a series of nitrobenzodithiacrown ethers with macrocycles of different size. The structures of three ethers were established by X-ray diffraction. A new method was developed for the synthesis of nitrobenzomonothia-15-crown-5 ether. Nitro derivatives of benzodithiacrown ethers were tested as reagents for extraction of palladium(II), platinum(IV), and rhodium(III) from hydrochloric acid solutions. Extraction of Pd^II salts was found to be highly selective compared to that of Pt^IV and Rh^III salts. Benzodithia-15-crown-5 ether is the most efficient extractant for palladium(II). Reduction of nitrobenzothiacrown ethers with hydrazine hydrate in the presence of a platinum catalyst afforded their amino derivatives. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 958–966, May, 2007.     

Synthesis and Complexing Properties of Novel Crown Ethers and Thiacrown Ethers Incorporating New Heterocyclic Moieties

The synthesis of some novel crown and thiacrown ethers via the reaction of 2,3-bis(4-hydroxyphenyl) or 2,3-bis(4-mercaptophenyl)quinoxalines and pyridopyridazine with diethylene and triethylene glycol ditosylate is described. The complexing ability of compounds 5b and 5h, as the representatives of both groups of compounds, with alkali and alkali earth metal cations were measured by the solvent extraction method. The results showed that crown ether 5b comparatively had more affinity towards the Mg²⁺ cation, while thiacrown ether 5h had greater affinity towards the Ca²⁺ cation.     

Bis(crown-6)calix[4]arene/Cs+ Coordination Chemistry in NPME Solution

NMR spectroscopy was used to show that the symmetry of the crown ether bis(C6) is increased by an increase of the alkali metal cation radius. The EXAFS spectrum demonstrates that a seven oxygen atom coordinated configuration is present in the bis(C6)/Cs⁺/NPME system, where NPME denotes o-nitrophenylmethyl ether. The seventh oxygen in this complex, besides the six crown ether oxygens of bis(C6), may come either from a H₂O molecule or an NO₃⁻ ion.     

peri-naphthylenediamines

First indirect evidence for the formation of a radical cation of 1,8-bis(dimethylamino)naphthalene (“proton sponge”) in reactions with HNO₃, HNO₂, NO₂, and I₂ has been obtained. In all cases, the products of reaction of the radical cation with nucleophiles and/or its dimer, 4,5,4′,5′-tetrakis(dimethylamino)-1,1′-binaphthyl, have been isolated. 4-Chloro-1,8-bis(dimethylamino)naphthalene has been regioselectively synthesized in high yield. For Part 24, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 320–324, February, 1998.     

Solid-phase oxidative halodecarboxylation of β-arylacrylic acids with the ceric ammonium nitrate—alkali halide system

The solid-phase oxidation of cinnamic, 4-methoxy- and 3,4-dimethoxycinnamic acids with Ce(NH₄)₂(NO₃)₆—MHal system leads to β-halostyrenes. Similar procedure in the absence of a metal halide results in a cleavage of the C=C bond giving the corresponding benzaldehydes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 114–118, January, 2008.     

Synthesis and application of new Schiff base Mn(III) complexes containing crown ether rings as catalysts for oxidation of cyclohexene and cyclooctene by Oxone

Six catalysts MnClL¹–MnClL⁶, containing two crown ether rings, were synthesised and characterised by IR spectroscopy and CHN microanalysis. A combination of Oxone, as oxidant, and these catalysts was used for the oxidation of cyclohexene and cyclooctene. Among the prepared catalysts, MnClL³ and MnClL⁴ exhibited the best catalytic efficiency. Catalysts MnClL¹, MnClL² and MnClL⁶ showed a moderate efficiency and MnClL¹ showed the lowest efficiency. Comparison of MmclL¹–MnClL⁴ and MnClL⁶ containing crown ether rings with an identical mixture of uncrowned complex MnClL⁷ [manganese N,N′-bis(salicylidene)ethylenediamine chloride] and crown ether 2 (4′-hydroxybenzo-15-crown-5), revealed a more important role for the crown ether than increasing solubility of Oxone in the organic phase. The effect on reaction times and chemical yields of temperature, pyridine as the axial base, and different alkali metal salts was also investigated.     

Ion-pair extraction of transition metal cations from aqueous media using novel N2O2-macrocyclic crown ligands

Three new macrocyclic crown ether ligands containing nitrogen–oxygen donor atoms were designed and synthesized from 1,4-bis(2′-formylphenyl)-1,4-dioxabutane and 4-nitro-o-phenylenediamine. Ion-pair extraction of metal picrates such as Ag⁺, Hg²⁺, Cd²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Co²⁺, and Pb²⁺ from aqueous phase to the organic phase was carried out using the novel ligands. The solvent effect over the metal picrate extractions was investigated at 25 ± 0.1 °C by using UV–visible spectrometry. The extractability and the values of the extraction constants (log K_ex) were determined for the extracted complexes.     

Synthesis of formyl derivatives of benzocrown ethers containing N,S, and O heteroatoms in the macrocycle

A method for the synthesis of 4-bromobenzodithia-15(18)-crown-5(6) and 4-bromobenzodiaza-15 (18)-crown-5(6) by condensation of 3,4-di(2-haloethoxy)bromobenzene with polyoxaalkanes containing terminal SH or NHMe groups was suggested. The method for the synthesis of formyl derivatives of benzocrowns containing N, S, and O heteroatoms in the macrocycle based on the metallation of appropriate bromo derivatives with BuⁿLi followed by treatment of the resulting organolithium intermediates with DMF was developed. Oximes and semicarbazones of benzaldehydes containing a crown ether fragment were obtained, and their transformation into the original aldehydes by treatment with KNO₂ in an acid medium was studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 121–128, January, 1995.This study was financially supported by the Russian Foundation for Basic Research (Grant No. 94-03-08-531) and the International Science Foundation (Grant M8Q000).     

Synthesis of formyl derivatives of benzodiazacrown ethers and benzocryptands

A simple and convenient procedure was developed for the synthesis of formyl derivatives of benzodiazacrown ethers and benzocryptands by condensation of 3,4-bis(2-iodoethoxy)benzaldehyde with ,-oligooxaalkanediamines or diazacrown ethers in the presence of alkali metal carbonates under high-dilution conditions in various organic solvents and their mixtures with water. In the reactions giving rise to diazacrown ethers, alkali metal cations exhibit the negative template effect resulting in a decrease in the yield of the target product if the size of the cation matches well the size of the cavity of the crown ether formed. An N,N"-bis(carboxymethyl) derivative was prepared from the formyl derivative of benzodiaza-18-crown-6.     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study. 1. Conformers of arylazacrown ethers and their complexes with Ca2+ cation

Photoinduced recoordination of Ca²⁺ complexes of the photochromic azacrown ethers is studied by the density functional method. The study included model arylazacrown ethers containing various acceptor groups in the aromatic ring in the para position to the azacrown ether moiety and a real azacrown-containing styryl dye. It is found that both free azacrown ethers and their complexes can adopt two types of conformations: (1) axial conformations, in which the aromatic ring axis passing through the crown ether nitrogen N_cr and the opposite atom of the aromatic ring is perpendicular to the root-mean-square (RMS) plane of the crown ether (least-squares fitted plane for all the crown ether atoms), and (2) equatorial conformations, in which the aromatic ring axis only slightly deflects from the RMS plane of the crown ether. In the equatorial conformers, the metal cation is coordinated only to the O atoms of the azacrown ether cycle, the metal—nitrogen bond is broken, and N_cr is conjugated with the aromatic ring. In the axial conformers, the metal cation is additionally coordinated to N_cr. It is found that the presence of an acceptor group bearing a formal positive charge decreases the relative energy of the equatorial conformer and favors metal—nitrogen bond dissociation, which results in the recoordination of the metal cation. However, a long distance between the charged group and N_cr has the reverse effect. The photoinduced recoordination observed in the alkaline-earth metal complexes of the photochromic azacrown ethers is explained by the transitions between the axial and equatorial conformers facilitated by the charge transfer in the excited state of the complex.     

Alkali metal cation complexation by 1,3-alternate,mono-ionisable calix[4]arene-benzocrown-6 compounds

Alkali metal cation extraction behaviour for two series of 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds is examined. In Series 1, the proton-ionisable group (PIG) is a substituent on the benzo group of the polyether ring that directs it away from the crown ether cavity. In Series 2, the PIG is attached to one para position in the calixarene framework, thereby positioning it over the crown ether ring. Competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform shows high Cs⁺ efficiency and selectivity. Single-species extraction pH profiles of Cs⁺ for Series 1 and 2 ligands with the same PIG are very similar. Thus, association of Cs⁺ with the calixcrown ring is more important than the position of the PIG relative to the crown ether cavity. Solid-state structures of two unionised ligands from Series 2 are presented. Also described is a crystal containing two different ionised ligand–Cs⁺ complexes.     

Synthesis and applications of 3,4-dihydroxy-2,5-bis-(2′-(4′-substituted-oxazolinyl)) furan

Three 3,4-dihydroxy-2,5-bis-(2′-(4′-substituted-oxazolinyl)) furans were synthesized at 90%–94% yields from reaction of 3,4-dihydroxyfuran-2,5-dicar-boxylic acid or its dimethyl ester with chiral β-amino alcohol via a one-step process. Their chemical structures were determined by ¹H NMR, IR, MS, and elemental analysis. With these chiral bisoxazoline ligands, the asymmetric reductive reaction of β-acetonaphthalene with KBH₄ or NaBH₄ was preliminarily studied. The enantiomeric excess of the reduction product was up to 83.2% with cyclohexane as the solvent, the molar ratio of ligand: reductive agent: β-acetonaphthalene is 0.04:1.6:1, and 72-hours reaction time at 0°C. Furancontaining bisoxazoline with 4-benzyl on oxazoline rings exhibited higher enatioselectivity than congeneric bisoxazolines with 4-ethyl on oxazoline rings. __________ Translated from Chinese Journal of Applied Chemistry, 2005, 22(12) (in Chinese)     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.     

Alkali cation binding of polymers with different sized crown ethers and photodimerizable units

The polymers which have different sized crown ethers as alkali cation binding sites and photodimerizable cinnamoyl units were prepared by the cationic copolymerization of corresponding monomers. The crown–cation complexation ratio (1:1 or 2:1) was investigated by measuring quantum yields ? of the photodimerization of the crown-connected cinnamoyl units in the presence of alkali metal chlorides and also by measuring the shift of λ_max of alkali metal picrates in THF on addition of the crown polymers. A significant 1:2 complex formation of alkali cations with two different sized crown ether units in the side chain of the polymers was confirmed. The alkali metal cation binding ability and selectivity of the polymers, which were studied by a method of picrate salts extraction, were markedly different from those expected from the combination of polymers of same ring-size crown ether units. When irradiated with ultraviolet (UV) light, the cinnamic acid ester groups of the polymers caused dimerization even in dilute solutions. The cation binding ability of the polymers was largely enhanced by the photodimerization of the cinnamoyl moieties with suitable template cations.     

Action of HCl on 3-hydroxypyrazolo(iso)quinolines to give 1-chloropyrazoles: evidence for an addition–elimination mechanism by ab initio calculations in gas phase and water

 Addition–elimination reactions involving a nucleophile and a remote leaving group [S^H _N(AE)^tele] are well-known under basic conditions, especially amongst electron-poor six-membered heterocycles, but are less commonly encountered for five-membered heterocycles and are rare under acidic conditions. Concentrated HCl converts 1-hydroxy-1H-pyrazolo[3,4-c] isoquinoline and 1-hydroxy-1H-pyrazolo[3,4-c]quinoline into 3-chloro-1H-pyrazolo[3,4-c]isoquinoline and 3-chloro-1H-pyrazolo[3,4-c]quinoline, respectively. However, apparently neither the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)-quinolines nor the parent 1-hydroxypyrazole undergo this reaction. Additionally, all these systems are refractory under basic conditions. We present a plausible mechanism for the reaction, involving the 3-addition of Cl^- to the diprotonated heterocycle, followed by the elimination of water. Calculations of the initial transition states and intermediates, using optimisation at B3LYP/6-311+G(d,p), including thermochemistry [HF/6-31+G(d)], and single-point Poisson–Boltzmann self-consistent reaction field determination of the free energy of solvation (Jaguar Poisson–Boltzmann self-consistent reaction field), support this mechanism and reproduce the observed order of reactivity, the addition step being 2–4 kcal less favourable for the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)quinolines and provide a rationalisation for the role of strong acid. Received: 27 June 2002 / Accepted: 6 September 2002 / Published online: 14 February 2003     

Metal ion complexation in acetonitrile by cone,di-ionised calix[4]arene-1,2-crown ethers with two pendant dansyl fluorophores

Four cone calix[4]arene-1,2-crown ethers each with two ionisable side arms containing dansyl groups are synthesised. The crown ether ring on the lower rim is varied from crown-4 to crown-5 with hydrogen or tert-butyl groups on the para position of the upper rim. Di(tetramethylammonium) salts of the di-ionised ligands are utilised for spectrofluorimetric titration experiments in MeCN. The influence of alkali metal, alkaline earth metal and selected transition and heavy metal (Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) cations on the spectroscopic properties of the two dansyl groups linked to the lower rim of the conformationally locked, di-ionised calix[4]arene-1,2-crown ether frameworks is investigated by emission spectrophotometry. All of the metal cations induce red shifts in the emission spectra of the di-ionised ligands. The metal cations produce enhancement or quenching of the fluorescence emissions. Changes in the fluorescence emission as a function of the metal cation identity, the lower rim crown ether ring size and the absence or presence of upper rim tert-butyl groups are investigated.     

Enantioselective Oxidation of Sulfides Catalyzed by Chiral MoV and CuII Complexes of Catechol-Appended β-Cyclodextrin Derivatives in Water

The two modified β-cyclodextrin (β-CD) derivatives having catechol-type ligand (2,3- and 3,4-dihydroxy groups on the benzoate ring) were synthesized. The chiral catalytic activity of their Mo^V and Cu^II complexes was examined in the asymmetric oxidation of aromatic sulfides using hydrogen peroxide in water (pH 6.0). The oxidation with the Mo^V complexes of two β-CD derivatives were more accelerated than that with the Cu^II complexes. The sign of the optical rotation of the sulfoxides obtained in the above two cases showed the opposite configuration in the oxidation of the same sulfide. The difference of the enantioselectivity appeared also between the two complexes of the 2,3- and 3,4-dihydroxybenzoate derivatives with the same metal ion. While the use of the Mo^V complexes with the catechol derivatives yielded the sulfoxides with 35–65% ee, the use of the Cu^II complexes gave the products with the␣opposite configuration at 26–52% ee. The chiral induction in the oxidation, observed conversely between the␣catalysts, was reflected on the chiral conformation of the respective metal catalysts, showed in Induced Circular Dichroism (ICD) spectra. The highest optical yield, 65%, was observed in the oxidation of butyl phenyl sulfide using the catalytic amount (0.1 equiv) of the Mo^V complex with mono-6-O-(3,4-dihydroxybenzoyl)-β-CD. The reaction gave predominantly the (S)-sulfoxide in 95% chemical yield.     

Synthesis and Complexing Properties of <Emphasis Type="Italic">N,N</Emphasis>′-Bis(2-hydroxyethyl) Diaza Crown Ethers

The stability constants of complexes of 12-, 15-, and 18-membered diaza crown ethers, N,N′-dimethyl diaza crown ethers, and N,N′-bis(2-hydroxyethyl) diaza crown ethers with alkali and alkaline-earth metal ions in 95% aqueous methanol at 25°C were determined. The stability of the complexes of unsubstituted diaza crown ethers with alkali metal cations is low, probably because of stabilization of the exo,exo conformation of the ligands due to interaction of the nitrogen lone electron pairs with the solvent. The complexes with the double-charged cations are appreciably more stable. N,N′-Dimethyl diaza crown ethers form stable complexes with all the ions studied. As compared to the dimethyl derivatives, N,N′-bis(2-hydroxyethyl) diaza crown ethers form more stable complexes with the Na⁺, K⁺, Ca²⁺, Sr²⁺, and Ba²⁺ ions, which is due to participation of the side hydroxyethyl groups in the coordination.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005, pp. 665–669.Original Russian Text Copyright © 2005 by Kulygina, Vetrogon, Basok, Luk’yanenko.     

Reduction of silver cation in the cavity of diaza-18-crown-6: A theoretical study

The structure and stability of diaza-18-crown-6 (1) complex with silver cation was studied by the density functional method with the PBE functional. The reduction of the cation in the macrocycle cavity was simulated and possible stability of the resulting van der Waals complex of the crown ether 1 with silver atom was analyzed. It is shown that, after electron capture, two equilibrium conformers of Ag⁺·1 give two structures locally stable with respect to the dissociation into the silver atom and the crown ether in its nearest equilibrium conformation. One of the neutral structures, that of the C _s symmetry, corresponds to a global minimum on the potential energy surface of the Ag⁰—1 system. It ensures the thermodynamic stability of the reduced complex with respect to dissociation. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 395–399, March, 2007.     

A molecular switch based on acid and base promoted, cation governed binding in a crown ether threaded rotaxane

A rotaxane, containing both oligo ethylene glycol and secondary ammonium cation binding sites for a threaded crown ether, has been prepared. ¹H NMR spectroscopy has been used to show that the crown ether moiety in the rotaxane undergoes acid-base and alkali metal cation dependent switch from binding at the ammonium cation position to cooperative binding to the metal cation at the oligo ethylene glycol site.