14098-24-9Relevant articles and documents
Competition between Catalysts and Inhibitors in Crown Ether Formation and Other Reactions of Associated Substrates
Vitali, Chiara Antonini,Masci, Bernardo
, p. 1070 - 1071 (1989)
Competition between non-covalent catalysts and/or inhibitors helps quantitative investigation in crown ether formation, and promises to be a useful tool when dealing with associated rective substrates in general.
Model System for the Template Effect of Alkali and Alkaline-Earth Metal Ions on the Formation of Benzo-18-crown-6 in MeOH Solution
Ercolani, Gianfranco,Mandolini, Luigi,Masci, Bernardo
, p. 6146 - 6149 (1983)
Alkali and alkaline-earth metal ions exert a remarkable catalytic effect (template effect) on the cyclizatiion of o-hydroxyphenyl 3,6,9,12-tetraoxa-14-bromotetradecyl ether (ArOH) to benzo-18-crown-6 (B18C6) in MeOH solution.This phenomenon is interpreted as resulting from two opposing factors, a rate-enhancing factor due to an increased proximity of chain ends in the cation-associated precursor ArO- and a rate-retarding factor due to interaction of the nucleophilic end of ArO- with the metal ion.Combination of previous equilibrium data with kinetic measurements from the present work provides a complete set of equilibrium constants for association of seven cations Na+, K+, Rb+, and Cs+ and Ca2+, Sr2+, and Ba2+ with the four ligands ArOH, ArO-, B18C6, and T, the latter being the transition state for cyclization.Following our earlier suggestion, according to which the proximity effect is viewed as a sort of macrocyclic effect, i. e., the one in which the cyclic ligand is T and the acyclic ligand is ArO-, we now present an extrathermodynamic treatment indicating that the magnitude of the above macrocyclic effect is well represented by the KB18C6/KArOH ratio.This ratio provides an estimate for the upper limit of the template effect.The actually observed values are lower by a factor of ca. 4 because of reduction of nucleophilicity due to cation association.
Stable supramolecular dimer of self-complementary benzo-18-crown-6 with a pendant protonated amino arm
Kryatova, Olga P.,Kryatov, Sergey V.,Staples, Richard J.,Rybak-Akimova, Elena V.
, p. 3014 - 3015 (2002)
The novel 4′-(ammoniummethylene)benzo-18-crown-6 cation was synthesized as a hexafluorophosphate salt and found to exist as a cyclophane-like dimer in the solid state, gas phase and in acetonitrile solution.
Template Effects. 3. The Quantiative Determination of the Catalytic Effects of Alkali and Alkaline Earth Cations in the Formation of Benzo-18-crown-6 in Methanol Solution
Ercolani, Gianfranco,Mandolini, Luigi,Masci, Bernardo
, p. 2780 - 2782 (1981)
Cyclization of the conjugate base of o-hydroxyphenyl 3,6,9,12-tetraoxa-14-bromotetradecyl ether to benzo-18-crown-6 in methanol solution has been found to be strongly and specifically accelerated by added alkali and alkaline earth bromides.The observed accelerations range from 13.2 for Cs+ to a spectacular 540 for Sr2+.The reported data refer to conditions in which the rate is independent of cation concentration, thus providing for the first time a quantitative determination of the template effect of added cations in the formation of a macrocyclic polydentate ligand.The different catalytic abilities as observed for the different cations are tentatively discussed in terms of a combination between proximity of the reactive ends in the bifunctional precursor complexed around the metal ion, and chemical factors arising from the extent of interaction of the cation with the nucleophilic oxide ion.
Catalytic Reductions Without External Hydrogen Gas: Broad Scope Hydrogenations with Tetrahydroxydiboron and a Tertiary Amine
Korvinson, Kirill A.,Akula, Hari K.,Malinchak, Casina T.,Sebastian, Dellamol,Wei, Wei,Khandaker, Tashrique A.,Andrzejewska, Magdalena R.,Zajc, Barbara,Lakshman, Mahesh K.
supporting information, p. 166 - 176 (2020/01/02)
Facile reduction of aryl halides with a combination of 5% Pd/C, B2(OH)4, and 4-methylmorpholine is reported. Aryl bromides, iodides, and chlorides were efficiently reduced. Aryl dihalides containing two different halogen atoms underwent selective reduction: I over Br and Cl, and Br over Cl. Beyond these, aryl triflates were efficiently reduced. This combination was broadly general, effectuating reductions of benzylic halides and ethers, alkenes, alkynes, aldehydes, and azides, as well as for N-Cbz deprotection. A cyano group was unaffected, but a nitro group and a ketone underwent reduction to a low extent. When B2(OD)4 was used for aryl halide reduction, a significant amount of deuteriation occurred. However, H atom incorporation competed and increased in slower reactions. 4-Methylmorpholine was identified as a possible source of H atoms in this, but a combination of only 4-methylmorpholine and Pd/C did not result in reduction. Hydrogen gas has been observed to form with this reagent combination. Experiments aimed at understanding the chemistry led to the proposal of a plausible mechanism and to the identification of N,N-bis(methyl-d3)pyridin-4-amine (DMAP-d6) and B2(OD)4 as an effective combination for full aromatic deuteriation. (Figure presented.).
A practical synthesis of benzocrown ethers under phase-transfer catalysis conditions
Bogaschenko, Tatyana,Basok, Stepan,Kulygina, Catherine,Lyapunov, Alexander,Lukyanenko, Nikolay
, p. 2266 - 2270 (2007/10/03)
Convenient and effective procedures for the synthesis of benzo-12-crown-4, benzo-15-crown-5, benzo-18-crown-6, benzo-21-crown-7 and benzo-24-crown-8 under phase-transfer catalysis conditions have been developed.
Synthesis of formyl derivatives of benzocrown ethers containing N, S, and O heteroatoms in the macrocycle
Gromov, S. P.,Fedorova, O. A.,Vedernikov, A. I.,Samoshin, V. V.,Zefirov, N. S.,Alfimov, M. V.
, p. 116 - 123 (2007/10/02)
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. - Key words: 4'-bromobenzocrowns, synthesis, metallation; 4'-formylbenzocrown ethers; semicarbazones and oximes of 4'-formylbenzocrown ethers.
SYNTHESIS AND ALKALI METAL CATION COMPLEXATION BY BENZOCROWN ETHERS
Czech, Bronislaw P.,Czech, Anna,Knudsen, Brian E.,Bartsch, Richard A.
, p. 717 - 722 (2007/10/02)
New or improved synthetic routes to several benzocrown ethers and alkali metal picrate extraction data for eight benzocrown ethers with varying sizes are reported.
Synthesis of 4'-Vinylbenzo-3n-crown-n Ethers (4<=n<=10)
Talma, Auke G.,Vossen, Huib van,Sudhoelter, Ernst J. R.,Eerden, Johan van,Reinhoudt, David N.
, p. 680 - 683 (2007/10/02)
4'-Vinylbenzo-3n-crown-n ethers (4=n=10) are prepared by a "Cs-templated" cyclization reaction of catechol with dimesylates of oligoethylene glycols, acetylation of the resultant benzo-3n-crown-n ethers (4=n=10), reduction of the acyl group, and dehydration of the resultant alcohols with pyridinium tosylate.
The Complexation of the Diquat Dication by Dibenzo-3n-crown-n Ethers
Colquhoun, Howard M.,Goodings, Eric P.,Maud, John M.,Stoddart, J. Fraser,Wolstenholme, John B.,Williams, David J.
, p. 607 - 624 (2007/10/02)
Spectrophotometric investigations of equimolar mixtures of diquat bis(hexafluorophosphate) (2) and a range of dibenzo-3n-crown-n ethers in acetonitrile reveal the existence of charge-transfer absorption bands at ca. λmax 400 nm.These absorptions are attributable to intermolecular ?-? charge transfer between the electron-rich catechol units of the dibenzo-crown ethers and the electron-deficient bipyridinium ring system of the diquat dication.The qualitative conclusion from these experiments, that the most stable 1:1 complex is formed between dibenzo-30-crown-10 (14) and diquat bis(hexafluorophosphate) (2), led to the isolation from dichloromethane methanol-n-heptane of red crystals of 2 suitable for X-ray crystallography.Although the crystal structure analysis revealed that there are two independent sets of 1:1 complexes (I and II) in the unit cell, the gross structural features of the two complexes are very similar.In addition to the paralell alignment of their three aromatic rings to accommodate the stabilising intermolecular ?-? charge-transfer interaction, there is probably some further host-guest stabilisation to be gained on account of favourable electrostatic interactions between the phenolic oxygen atoms in the host and the nitrogen atoms in the pyridinium rings of the guest.Moreover, there is some evidence for weak C-H...O hydrogen bonding involving principally H-6 and H-6' on the bipyridinium ring system of the guest and certain -CH2OCH2- oxygen atoms in the host.As evidenced by 1H n.m.r. spectroscopy in CD3COCD3, these non-covalent bonding interactions are probably responsible for the formation of stable and ordered 1:1 complexes with similar gross structural features in solution, at least in the cases where dibenzo-30-crown-10 (14), dibenzo-33-crown-11 (15), and dibenzo-36-crown-12 (16) are the hosts.Further evidence for the 1:1 stoicheiometry of these solution complexes, as well as for the complex involving dibenzo-27-crown-9 (13), has come from equilibrium constant measurements for the association between the dibenzo-3n-crown-n (n = 9-12) hosts (13)-(16) and diquat bis(hexafluorophosphate) (2) in acetone.A quantitative treatment of the charge-transfer absorption bands at 400 nm, which affords Ka values of 410, 17500, 10800, and 2000 M-1 for n = 9, 10, 11, and 12, respectively, provides convincing quantitative evidence for (a) 1:1 stoicheiometry and (b) the relative stabilities of the 1:1 complexes in solution.In the case of dibenzo-24-crown-8 (11), a complex of 2:1 (guest-host) stoicheiometry is believed to be formed in acetone with a Ka value of 385000 M-2, as shown by a successfull quantitative treatment of the charge-transfer absorption data by an independent method.
