14098-24-9Relevant articles and documents
Metal fluorides as base for the "templated" synthesis of crown ethers
Reinhoudt,de Jong,Tomassen
, p. 2067 - 2070 (1979)
-
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.
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.).
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.
