Macrocyclic Ethers Research Articles

ChemInform Abstract: Transition Metal Templates as Guides for Cycloadditions

The improvement of synthetic efficiency requires the development of more chemo-, regio-, diastereo- and enantioselective methods. Transition metal templates form the equivalent of an 'active site' to impose selectivity upon reacting organic systems. Such effects will be examined within the context of cyclization reactions. The first part examines cyclization reactions invoking intramolecular carbametallation. Catalytic reactions involving at least three different mechanisms and two different metals provide five- and six-membered rings from enynes and diynes. A second strategy invokes transition metal templates to facilitate macrocyclization. Formation of macrocarbocycles, macrolactones and macrocyclic ethers and amines illustrates the versatility of this approach. Most importantly, many of the macrocyclizations proceed at normal concentrations of 0.25-0.50 M. The third strategy invokes cycloadditions. A transition metal equivalent to the Diels-Alder reaction permits formation of odd membered rings by [2n + 3] cycloadditions for n = 1, 2 and 3. The applicability that such methods have in devising new synthetic strategies towards biologically important natural products will be illustrated.

Complexes of 18-crown-6 with oxonium ions derived from transition metal chlorides and hydrochloric acid: 18-crown-6.H3O+. FeCl4−, 18-crown-6.H3O+.InCl4−, (18-crown-6.H3O+)2.Pd2Cl62−

The macrocyclic polyether 18-crown-6 forms complexes with hydrates of strong acids derived from transition metal chlorides and hydrochloric acid. The following charged-component complexes have been isolated and characterized: 18-crown-6.H3O+.FeCl4−, 18-crown-6.H3O+.InCl4−, and (18-crown-6.H3O+)2.Pd2Cl62−. X-ray diffraction study of the palladium complex is reported. The oxonium ion is located at the center of the macrocyclic ether cavity and the symmetry of the ring is close to D3d. Keywords: 18-crown-6 complexes, oxonium ions, X-ray diffraction, crystal structure

A long-range intramolecular functionalization by alkoxyl radicals: a long-range intramolecular hydroxylation of C(25) of cholestane side chain

Alkoxyl radicals generated by the irradiation of hypoiodites of 5α-chlolestan-7α-yl-4-(hydroxyphenylmethyl)-phenylacetates and 5α-cholestan-7α-yl-3-[4-(hydroxyphenylmethyl)phenyl] propionates, respectively, abstracted a hydrogen from the remote C(25) of their cholestane side chain to give novel macrocyclic ether lactones which gave 5α-cholestane-7α, 25-diol by reduction with Na and liquid ammonia in good yields.

Macrocycle reorientation in solid 18-crown-6 complexes detected by 1H and 13C n.m.r. spectroscopy

Solid state 1H and 13C n.m.r. spectra of 18-crown-6 complexes indicate reorientational motions of the macrocyclic ether, at or near room temperature, in contrast with apparently static X-ray structures.

Synthesis and cation-binding abilities of novel polyquinane crown ethers containing a bis-acetal ether functionality

New macrocyclic ether hosts bearing a ‘bis-acetal ether’ functionality and a lipophilic posterior have been synthesised from the readily available cis,syn,cis -triquinane dione 1 and ethylene glycols in one step. Complexation characteristics and ability of these host molecules to translocate cations across phospholipid bilayer vesicles or liposomes has been studied.

13C-dipole dipole relaxation time and internal motions of oligo cyclicethers and ether-esters. Part IV. The mechanism and activation energies of the ring Pseudorotation of 15.Crown.5, 18.Crown.6 and 2,6-dioxo-18.crown.6.

The 13C dipole-dipole relaxation time values of 1,4,7,10,13- pentaoxacyclopentadecane,(15.Crown.5) and 1,4,7,10,13,16-hexaoxa cyclooctadecane,(18.crown.6) in CDCl 3 and 2,6-dioxo-1,4,7,10,13,16 -hexaoxacycloctadecane,(2,6-do-18.crown.6) were determined in CD 2Cl 2 at 15 MHz of various temperatures by inversion recovery method. The results observed in frequency range of ( W O+ W H 2T 2«1 extreme narrowing conditions were explained in terms of internal motions of macrocyclic backbone and the ring isomerization. The free energies obtained from the 13C dipole-dipole relaxation time measurments were assigned properly to the pseudorotation rate and the conformational barrier of the oxyethylene groups of the macrocyclic ethers and ether-ester. The segmental motion CC and CO bonds of dioxo-hexaoxa ether, observed as the specific T DD 1 and energy barrier of different 13C nuclei was also discussed.

The Synthesis and Structures of Cyclic Oligoether-Esters. 4. The Formation and Conformation of Macrocyclic Ether Rings of α, β-Dioxo-cyclopolyoxa Oligo(Ether-Esters)

Abstract The cyclic ether-ester formation from the condensation of oxalyl chloride with tri and tetraethyleneglycols were tried in benzene/dioxan solutions in the presence of pyridine. The conformation of the ether linkage of the isolated products were investigated by high resolution 13C, 1H and 2D-COSY spectra.

Transition metal templates as guides for cyclizations

The improvement of synthetic efficiency requires the development of more chemo-, regio-, diastereo- and enantioselective methods. Transition metal templates form the equivalent of an ‘active site’ to impose selectivity upon reacting organic systems. Such effects will be examined within the context of cyclization reactions. The first part examines cyclization reactions invoking intramolecular carbametallation. Catalytic reactions involving at least three different mechanisms and two different metals provide five- and six-membered rings from enynes and diynes. A second strategy invokes transition metal templates to facilitate macrocyclization. Formation of macrocarbocycles, macrolactones and macrocyclic ethers and amines illustrates the versatility of this approach. Most importantly, many of the macrocyclizations proceed at normal concentrations of 0.25-0.50 m . The third strategy invokes cycloadditions. A transition metal equivalent to the Diels-Alder reaction permits formation of odd membered rings by [2« + 3] cycloadditions for n = 1, 2 and 3. The applicability that such methods have in devising new synthetic strategies towards biologically important natural products will be illustrated.

Ionic complexation of N 2O 4 by 18-crown-6

An ionic complex has been obtained from N 2O 4 in the presence of the macrocyclic ether 18-crown-6. This crystalline compound has been shown from its Raman spectrum to have the formula NO +·crown·H(NO 3) 2 −, with the nitrosonium ion closely associated with the crown ether rather than with the hydrogen dinitrate accompanying ion. This adduct decomposes readily in moist air to give the known complex (HNO 3·H 2O) 2·crown.

ChemInform Abstract: Syntheses of Macrocyclic Ethers

ChemInformVolume 19, Issue 21 Reviews ChemInform Abstract: Syntheses of Macrocyclic Ethers H.-J. ALTENBACH, H.-J. ALTENBACH D-4790 PaderbornSearch for more papers by this author H.-J. ALTENBACH, H.-J. ALTENBACH D-4790 PaderbornSearch for more papers by this author First published: May 24, 1988 https://doi.org/10.1002/chin.198821343Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue21May 24, 1988 RelatedInformation

ChemInform Abstract: Synthesis and Transannular Diels‐Alder Reaction of a cis‐trans‐trans 13‐Membered Macrocyclic Trienone.

AbstractCyclization of the ω‐chloroalkadienonecarboxylate (II), prepared from (I), yields the macrocyclic ether (III) and the keto diene (IV).

ChemInform Abstract: Proton‐Ionizable Crown Compounds. Part 13. Synthesis and Structural Studies of Crown Compounds Containing the Triazole Subcyclic Unit and Lipophilic Substituents.

AbstractSome macrocyclic ethers such as (III) which contain the 1,2,4‐triazole moiety are prepared.

The determination of stability of macrocyclic ether complexes by use of 13C dipole-dipole relaxation time measurements.

In order to determine the stability of the complexes of macrocyclic oligoethers with alkaline and alkaline earth cations we have recently developed a NMR method which determined the equilibrium constants of complexing solutions by measuring the 13 C dipole-dipole relaxation times of the macrocyclic ethers in cationic solutions. We now report the equilibrium constant of 12.crown.4 complexing with Li + in methanol −d and free energies of complexing of Li + in methanol −d and Ca 2+ and Mg 2+ in DOH which were determined by the aid of given method. Experimental results were discussed from the view of crown ether complexation and the basis of the relaxation times concept.

Transition metal templates as guides for cycloadditions

Abstract

Complex formation of methyl viologen and diquat with macrocyclic ether dibenzo-24-crown-8

The complex formation of a coplanar N, N'-ethylene-bipyridinium dication and dibenzo-24-crown-8 in methanol was detected by electrochemical techniques. It is demonstrated here that a coplanar ring arrangement is not required for an efficient charge-transfer interaction between bipyridinium and crown. The much stronger complexation of methyl viologen was investigated by both electrochemical and spectral techniques. The presence of a benzene ring in the crown molecule is a condition for complex formation. The described complex exerts catalytic activity for the reduction of oxygen.

Complexes of 18-crown-6 macrocyclic ethers containing both an alkali metal phenoxide salt and phenol. Crown:salt:phenol ratios of 1:1:1 and 1:1:2

Sodium and potassium phenoxide, in the presence of one equivalent of dicyclohexano-18-crown-6 (cis–anti–cis isomer) and dibenzo-18-crown-6, form complexes that have a ratio of 1:1:1 (crown:salt:phenol) in ethereal solvents containing excess phenol. On the other hand, complexes having 1:1:2 ratios (crown:salt:phenol) are obtained under the same conditions when the macrocycle is 18-crown-6 or dicyclohexano-18-crown-6 (cis–syn–cis isomer). When only one equivalent of phenol is present, then 1:1:1 complexes are obtained with 18-crown-6 and dicyclohexano- 18-crown-6 (cis–syn–cis isomer). No complexes containing only the metal salts were isolated from these solutions. The infrared spectral data obtained from the complexes show that the phenol hydroxyl hydrogens in the complexes form either strong or very strong hydrogen bonds. The nuclear magnetic resonance chemical shifts of the phenol protons in the complexes have been obtained from deuterated dimethoxyethane solutions. Comparisons are made with the chemical shifts of the phenol hydroxyl protons obtained from the corresponding solutions containing only the equivalent salt/phenol solutions.

Conformation of Dioxo-Polyoxa Cycloalkanes by1H NMR

Abstract The conformation of the macrocyclic polyoxo-oligo ethers and esters of cation binding ability have been known to play important role due to appropriate orientation of molecular orbitals cousing selective binding on the cationic radii. The oxygen dipoles are enabled to arrange their p orbitals to the direction of delocalised positive charge. The energy transfer -or exchange- between the ion and ligand shell determined the maximum stability and the stoichiometry of the complexation. Accordingly flexibility or the rigidity of the polyoxo-ether-ester ring cousing from the hindered rotation of cyclic lactone mostly determined the degree of association with the cation.

Determination of the Complexing Constants by the Aid of 13C Dipole-Dipole Relaxation Time Measurements. Part. III. Complexing of 15-Crown-5 and 18-Crown-6 with Na+,K+ and Ca2+ in DHOX

Abstract The association constants, Ka of KI, Nal and CaCl2 complexing with 1,4,7,10,13-pentaoxacyclopentadecane and 1,4,7,10,13,16-hexaoxacycloocta-decane in DHO were determined by the aid of 13C dipole-dipole relaxation time measurements. The mole fraction of the complexed ligand, PC were obtained by the use of the equation of 1/Tobs 1 - 1/T10 = PC (1/TO 1 - 1/T10) where the T10 and To 1 are the relaxation times of free and complexed macrocyclic ethers respectively. Ka values obtained from the above given equation depending on the cation concentration, [A+ O] typically reflected the relation between the cationic radius and cyclic ether ring size.

Homogeneous Polymerisation of Methylmethacrylate Initiated by Alkali Metal Salts of Methanol and t‐Butyl Alcohol in the Presence of Cryptands and Macrocyclic Crown Ether Compounds

AbstractThe polymerisation of methylmethacrylate initiated by alkali alkoxides is greatly promoted in the presence of macrocyclic compounds, cryptands and crown ethers. The solubility in toluene and the reactivity of alkoxides is enhanced by these complexing agents. Polymerisations have been carried out in a non‐polar solvent in the homogeneous phase.

Complexes of 18-crown-6 macrocyclic ethers obtained from ethereal solvents. Complexes of potassium and sodium salts with host:guest ratios of 1:2 and 1:3

This paper describes the synthesis, in ethereal solvents, of the complexes of 18-crown-6, the cis–syn–cis and the cis–anti–cis isomers of dicyclohexano-18-crown-6, and dibenzo-18-crown-6 with the potassium and sodium salts of phenoxide and thiocyanate (as well as some potassium oximate salts). In general, the macrocycles break down the aggregates of the potassium salts so that the complexes of the contact ion pairs are isolated. The complex of the cis–anti–cis isomer of dicyclohexano-18-crown-6, however, which has a low stability constant, complexes the dimer of potassium phenoxide to give a complex with a 1:2 host:guest ratio. This appears to be the first example of a 1:2 host:guest ratio of a potassium salt with an 18-crown-6 macrocycle. There is a greater tendency for the complexes of sodium salts to have host:guest ratios less than 1:1. Thus, 18-crown-6 gives complexes with sodium phenoxide and sodium thiocyanate which have 1:3 and 1:2 host:guest ratios, respectively. Host:guest ratios of 1:2 are also obtained for the two above-mentioned isomers of dicyclohexano-18-crown-6 and for dibenzo-18-crown-6 with sodium phenoxide. Sodium thiocyanate gives complexes with either 1:1 or 1:2 host:guest ratios depending on the macrocycle. With dibenzo-18-crown-6, sodium thiocyanate gives a 1:1 complex in which one molecule of the solvent used is incorporated into the complex. The infrared and ultraviolet spectra of the complexes are discussed.