- Crown Ethers as New Catalysts in the Highly Regioselective Halogenative Cleavage of Epoxides with Elemental Halogen
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The regioselective ring opening halogenation of some epoxides using elemental iodine and bromine in the presence of a series of new synthetic macrocycle diamides and also dibenzo-18-crown -6, 18-crown-6, and aza-18-crown-6 has been studied. The epoxides were subject to cleavage by elemental halogen (I2 and Br2) in the presence of these catalysts under mild reaction conditions in various aprotic solvents. In this study, reagents and conditions have been discovered with which the individual halohydrins can be synthesized in high yield and with more than 95% regioselectivity. The results can be discussed in terms of a four-step mechanism: (1) formation of a charge-transfer complex between catalyst and halogen, (2) release of halogen nucleophile from the complex, (3) reaction of the active nucleophile at the less sterically-hindered site in the epoxide, and (4) regeneration of catalyst. The major advantages of this method are high regioselectivity, simple regeneration of catalyst and its reuse through several cycles without a decrease in activity, and ease of workup of the reaction.
- Sharghi, Hashem,Massah, Ahmad Reza,Eshghi, Hossein,Niknam, Khodabakhsh
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- Dynamic combinatorial libraries for the recognition of heavy metal ions
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We present the use of hydrazone dynamic combinatorial libraries (DCLs) to identify macrocyclic receptors that are selective for alkaline earth metal ions over alkali metal ions. In particular, the toxic heavy metal ions Sr 2+ and Ba2+/sup
- Klein, Joerg M.,Saggiomo, Vittorio,Reck, Lisa,Luening, Ulrich,Sanders, Jeremy K. M.
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supporting information; scheme or table
p. 60 - 66
(2012/01/06)
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- Efficient synthesis of macrocyclic dilactam crown ethers by fast addition method
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A simple and convenient method for preparing macrocyclic dilactam crown ethers containing N2O5, N3O3, N 3O4, N3O5 and N2O 10 donor atoms with 18-32 membered
- Rahimizadeh,Eshghi,Rostami,Faghihi
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- New fluorimetric alkali and alkaline earth metal cation sensors based on noncyclic crown ethers by means of intramolecular excimer formation of pyrene
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New fluorescent reagents, 2,2′-[oxybis(3-oxapentamethyleneoxy)]-bis[N-(1-pyrenylmethyl)benzamide)] (4) and its analogues (2, 3, and 5) which have two pyrenes at the both terminals of polyoxyethylene compounds, were synthesized, and their complexation behavior with alkaline earth cations was investigated by fluorescence spectrometry, fluorescence lifetimes, and 1H NMR spectrometry. These reagents (3-5) showed strong intramolecular excimer emissions around at 480 nm in the fluorescence spectra. On the complexation with alkaline earth metal cations, the increase of monomer emission around at 400 nm accompanied by the disappearance of intramolecular excimer emission of free reagents was observed. These reagents formed a 1:1 complex, and the order of complex formation constants was Ca2+ ? Sr2+ > Ba2+ > Mg2+ > Li+ for all reagents. 1H NMR spectra of these complexes with alkaline earth cations suggested the helical structures of the complexes. Fluorescence spectral changes at the formation of complexes depended on the chain length of the oxyethylene moiety and metal cations. In all cases, the formation of helical structures at the complexation was supported by the 1H NMR spectra.
- Suzuki, Yoshio,Morozumi, Tatsuya,Nakamura, Hiroshi,Shimomura, Masatsugu,Hayashita, Takashi,Bartsh, Richard A.
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p. 7910 - 7917
(2007/10/03)
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- Efficient synthesis of macrocyclic diamides
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Some new macrocyclic dibenzotrioxadiamides, tribenzotrioxadiamides and tetrabenzohexaoxatetraamide (1-9) have been prepared. Compounds (2-9) were obtained in the macrocyclization step by reacting the dicarboxylic acid dichloride (13) with appropriate diam
- Sharghi, Hashem,Eshghi, Hossein
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p. 913 - 922
(2007/10/02)
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