- Improved preparation of 24-crown-8
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An improved method for the preparation of 24-crown-8 is described. Cyclization at room temperature and purification of the crude product via an acetonitrile complex provides a much higher yield than those reported in the literature.
- Talanov, Vladimir S.,Bartsch, Richard A.
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Read Online
- Self-Assembly of Stimuli-Responsive [2]Rotaxanes by Amidinium Exchange
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Advances in supramolecular chemistry are often underpinned by the development of fundamental building blocks and methods enabling their interconversion. In this work, we report the use of an underexplored dynamic covalent reaction for the synthesis of stimuli-responsive [2]rotaxanes. The formamidinium moiety lies at the heart of these mechanically interlocked architectures, because it enables both dynamic covalent exchange and the binding of simple crown ethers. We demonstrated that the rotaxane self-assembly follows a unique reaction pathway and that the complex interplay between crown ether and thread can be controlled in a transient fashion by addition of base and fuel acid. Dynamic combinatorial libraries, when exposed to diverse nucleophiles, revealed a profound stabilizing effect of the mechanical bond as well as intriguing reactivity differences between seemingly similar [2]rotaxanes.
- Borodin, Oleg,Richter, Stefan,Robertson, Craig C.,Shchukin, Yevhenii,Von Delius, Max
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supporting information
p. 16448 - 16457
(2021/10/12)
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- Synthesis of a molecular charm bracelet via click cyclization and olefin metathesis clipping
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We describe the synthesis of a polycatenated cyclic polymer, a structure that resembles a molecular charm bracelet. Ruthenium-catalyzed ring-opening metathesis polymerization of an aminocontaining cyclic olefin monomer in the presence of a chain transfer agent generated an α,ω-diazide functionalized polyamine. Cyclization of the resulting linear polyamine using pseudo-high-dilution coppercatalyzed click cyclization produced a cyclic polymer in 19% yield. The click reaction was then further employed to remove linear contaminants from the cyclic polymer using azide- and alkyne-functionalized scavenging resins, and the purified cyclic polymer product was characterized by gel permeation chromatography, 1H NMR spectroscopy, and IR spectroscopy. Polymer hydrogenation and conversion to the corresponding polyammonium species enabled coordination and interlocking of diolefin polyether fragments around the cyclic polymer backbone using ruthenium-catalyzed ring-closing olefin metathesis to afford a molecular charm bracelet structure. This charm bracelet complex was characterized by 1H NMR spectroscopy, and the catenated nature of the small rings was confirmed using two-dimensional diffusionordered NMR spectroscopy.
- Clark, Paul G.,Guidry, Erin N.,Chan, Wing Yan,Steinmetz, Wayne E.,Grubbs, Robert H.
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supporting information; experimental part
p. 3405 - 3412
(2010/05/01)
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- Synthesis and Characterization of Large (30-60-Membered) Aliphatic Crown Ethers
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We report a new synthetic approach to large (30-72 membered) crown ethers based on isolation of the small and large cyclic polyethers made by combination of 1 mol or 2 mol each, respectively, of oligo(ethylene glycol)s and oligo(ethylene glycol) ditosylates.The advantages of this approach are the use of readily available glycols as starting materials and the ability to optimize the procedure for selective production of either macrocycle, producing yields superior or comparable to previous methods.At higher reaction temperatures the large crown ether is preferentially formed.This approach has been used to produce the crown ethers on 100-g scales.Purification was achieved by a combination of filtration through silica gel, treatment with a polymeric acid chloride, and recrystallization techniques, avoiding standard column chromatography.The pure crown ethers, 60-crown-20, 48-crown-16, 42-crown-14, 36-crown-12, and 30-crown-10, were characterized by melting points, 1H- and 13C-NMR, elemental analysis, and/or MS, GC-MS, and TGA-MS.Melting points were as much as 26 deg C higher than previously reported for these crown ethers.All the aliphatic crown ethers larger than 18-crown-6 decompose upon heating in air at ca. 200 deg C.
- Gibson, Harry W.,Bheda, Mukesh C.,Engen, Paul,Shen, Ya Xi,Sze, Jean,et al.
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p. 2186 - 2196
(2007/10/02)
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- TEMPLATE EFFECTS. 7. LARGE UNSUBSTITUTED CROWN ETHERS FROM POLYETHYLENE GLYCOLS: FORMATION, ANALYSIS, AND PURIFICATION
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Through the reaction of polyethylene glycols with tosyl chloride and heterogeneous KOH in dioxane not only coronands from crown-4 to crown-8 can be obtained but also larger homologues.A systematic investigation has shown that: i) crown-9 and crown-10 can be formed from nona- and deca-ethylene glycol, respectively, and isolated in pure form; ii) the whole series of polyethylene glycols from tri- to deca-ethylene glycol yields not only the corresponding crown ethers but also higher cyclooligomers that can be analyzed up to about crown-20 by glc: in particular crown-12 and crown-16 were obtained from tetraethylene glycol and purified by column chromatography on cellulose; iii) the reaction, as applied to commercial mixtures of polyethylene glycols (from PEG 200 to PEG 1000), gives fairly high yields of crown ethers also in the region of large ring sizes.The contribution of the template effect of K(+) ion and the cyclooligomerization reactions for the various ring sizes are discussed.
- Vitali, Chiara Antonini,Masci, Bernardo
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p. 2201 - 2212
(2007/10/02)
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- Effect of Crown Ethers on the Selectivity of Electrophilic Aromatic Nitration
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Relative rates, isomer distributions, and partial rate factors have been determined for the nitration reactions of benzene, toluene, m-xylene, anisole, and mesitylene with tetrabutylammonium nitrate and trifluoroacetic anhydride in homogeneous CH2Cl2 solutions.The observed selectivity values have been compared with those obtained when 12-crown-4, 15-crown-5, 18-crown-6, 21-crown-7, or 24-crown-8 was added to the nitrating mixture.Small effects, if any, were observed with the smaller ligands, but marked variations in both substrate and positional selectivity appeared in the presence of 18-crown-6, 21-crown-7, and 24-crown-8.Such effects were found to depend on crown ether concentration and to vanish when KClO4 was added.A reaction scheme is proposed where both uncomplexed and complexed nitronium ion contribute to variable extents to the overall reaction.The selectivity of the crown ether associated electrophile relative to the unassociated one seems to result from the balance of two different effects: an increase in the sensitivity to the electronic effects of the substituents and a larger crowding in the transition state.The largest effects on selectivity were observed with 21-crown-7 which causes ortho-para-directing groups to act as essentially para-directing groups.Data for toluene nitration in the presence of 21-crown-7 fit very well the Brown selectivity relationship; the selectivity factor spanning a remarkably wide range on changing the crown ether concentration.
- Masci, Bernardo
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p. 4081 - 4087
(2007/10/02)
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- Crown Cation Complex Effects. 21. Spectral Evidence Bearing on the Interaction between Arenediazonium Cations and 21-Crown-7 in Nonpolar Solutions
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15-Crown-5 does not complex arenediazonium tetrafluoroborates, but 21-crown-7 is known to complex them more strongly than does 18-crown-6.Despite this, the infrared and ultraviolet band shifts for complex vs. noncomplexed forms are far smaller for the former than for the latter.It is suggested that instaed of the crown completely and tightly surrounding the diazonio function, the crown collars (nearly encircling) the diazonio group and then uses the remaining donor atom(s) either to solvate the terminal nitrogen atom or interact as a base with the ?-acidic aromatic ring, providing additional stability.Since the mode by which 18-crown-6 and 21-crown-7 solvate the diazonium ion in each case differs, the spectral manifestations of this interaction differ.
- Beadle, James R.,Khanna, Raj K.,Gokel, George W.
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p. 1242 - 1246
(2007/10/02)
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- The Synthesis of Unsubstituted Crown Ethers by the Reaction of Oligoethylene Glycols with Arenesulfonyl or Alkanesulfonyl Chlorides
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A new facile method of synthesizing crown ethers from oligoethylene glycols by treating them with arenesulfonyl or alkanesulfonyl chlorides in the presence of alkali metal hydroxide or alkoxide was described. 15-Crown-5 and 21-crown-7 were synthesized from pentaethylene glycol and heptaethylene glycol respectively in good yields, while 18-crown-6 was obtained from both hexaethylene glycol and triethylene glycol.Although the main product was 24-crown-8 in the reaction of tetraethylene glycol/TsCl/Na(K)OH in dioxane, 12-crown-4 was obtained in a moderate yield from the reaction of tetraethylene glycol/benzenesulfonyl chloride/t-BuOLi in t-BuOH.Furthermore, the analogous treatment of PEG 200 afforded a mixture of 15-, 18-, 21- and 24-crown ethers.The reaction conditions were investigated, and the scope of the reaction was discussed.
- Kuo, Ping-Lin,Kawamura, Norio,Miki, Masaki,Okahara, Mitsuo
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p. 1689 - 1693
(2007/10/02)
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- STUDIES OF CROWN ETHER COMPLEXES; ARYLDIAZONIUM ION COMPLEXES
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DNMR studies show that for complexation of aryldiazonium salts 21-crown-7 is the preferred host.
- Krane, Jostein,Skjetne, Tore
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p. 1775 - 1778
(2007/10/02)
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- POTASSIUM FLUORIDE ON ALUMINA AS BASE FOR CROWN ETHER SYNTHESIS
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Alumina coated with potassium fluoride was found to be an effective and practical reagent for the synthesis of some simple crown ethers.
- Yamawaki, Junko,Ando, Takashi
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p. 533 - 536
(2007/10/02)
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