- Synthesis and complexation properties of unsymmetrical sucrose-based receptors
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New unsymmetrical , sucrose-based diaza-crown ethers have been designed and prepared from monosilylated hexa-O-benzylsucrose derivatives. The enantioselective complexation of phenylethylammonium cations by these receptors was evaluated. It was demonstrated that the introduction of the amino group at the 6-position (glucose moiety) in sucrose increases the association constant for the S cation, but reduces the enantioselectivity. On the other hand, introduction of the amino group at the 6′-position (fructose moiety) in sucrose increases significantly the value of Ka and at the same time the high enantioselectivity is preserved. A new approach to sucrose-based macrocyclic receptors with an unsymmetrical arrangement of heteroatoms is presented. Their complexes with the (S)-α- phenylethylammonium cation are stronger than with the corresponding R cation. The enantioselectivity of the complexation depends on the position of the nitrogen atom(s) in the macrocyclic ring. Copyright
- Potopnyk, Mykhaylo A.,Jarosz, Slawomir
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- Lanthanum(III) triflate catalyzed direct amidation of esters
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Lanthanum trifluoromethanesulfonate is an effective single-component catalyst for synthesizing a variety of amides directly from esters and amines under mild conditions. Highly selective amidation of esters and amines, as well as catalyst-controlled amidation of esters, demonstrated the effectiveness of the catalyst system.
- Morimoto, Hiroyuki,Fujiwara, Risa,Shimizu, Yuhei,Morisaki, Kazuhiro,Ohshima, Takashi
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supporting information
p. 2018 - 2021
(2014/05/06)
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- α-Aminoamides as ligands in Goldberg amidations
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α-Aminoamides are shown to be useful as ligands in Goldberg amidations. A number of α-aminoamides are examined and the importance of substitution on the α-aminoamides is explored. Acetamide is focused on as the nucleophilic coupling partner due to its low cost, stability and convenience as a protecting group. The initial substrate scope for these catalysts is explored and includes electronically activated and deactivated aryl bromides, however o-substituted aryl bromides are problematic.
- Mitra, Aurpon W.,Hansen, Marvin M.,Laurila, Michael E.,Kolis, Stanley P.,Martinelli, Joseph R.
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supporting information
p. 6580 - 6583
(2013/11/19)
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- METHOD FOR PREPARATION OF AMIDES FROM ALCOHOLS AND AMINES BY EXTRUSION OF HYDROGEN
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The present invention relates to a method for preparation of carboxamides using alcohols and amines as starting materials in a dehydrogenative coupling reaction catalyzed by a ruthenium N-heterocyciic carbene (NHC) complex, which may be prepared in situ.
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Page/Page column 9
(2012/01/13)
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- Amide synthesis from alcohols and amines catalyzed by ruthenium N-Heterocyclic carbene complexes
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The direct synthesis of amides from alcohols and amines is described with the simultaneous liberation of dihydrogen. The reaction does not require any stoichiometric additives or hydrogen acceptors and is catalyzed by ruthenium N-heterocyclic carbene complexes. Three different catalyst systems are presented that all employ 1,3-diisopropylimidazol-2-ylidene (IiPr) as the carbene ligand. In addition, potassium iert-butoxide and a tricycloalkylphosphine are required for the amidation to proceed. In the first system, the active catalyst is generated in situ from [RuCl2(cod)] (cod = 1,5-cyclooctadiene), 1,3-diisopropylimidazolium chloride, tricyclopentylphosphonium tetrafluoroborate, and base. The second system uses the complex [RuCl 2(IiPr)(p-cymene)] together with tricyclohexylphosphine and base, whereas the third system employs the Hoveyda-Grubbs lst-generation metathesis catalyst together with 1,3-diisopropylimidazolium chloride and base. A range of different primary alcohols and amines have been coupled in the presence of the three catalyst systems to afford the corresponding amides in moderate to excellent yields. The best results are obtained with sterically unhindered alcohols and amines. The three catalyst systems do not show any significant differences in reactivity, which indicates that the same catalytically active species is operating. The reaction is believed to proceed by initial dehydrogenation of the primary alcohol to the aldehyde that stays coordinated to ruthenium and is not released into the reaction mixture. Addition of the amine forms the hemiaminal that undergoes dehydrogenation to the amide. A catalytic cycle is proposed with the {(I(Pr)RuII} species as the catalytically active components.
- Dam, Johan Hygum,Osztrovszky, Gyorgyi,Nordstrom, Lars Ulrik,Madsen, Robert
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supporting information; experimental part
p. 6820 - 6827
(2010/08/07)
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- The synthesis of amides and dipeptides from unprotected amino acids by a simultaneous protection-activation strategy using boron trifluoride diethyl etherate
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The reaction of l-phenylalanine (1) with boron trifluoride diethyl etherate and primary amines leads to the formation of amides via a cyclic boron intermediate. It is also possible to use the amino dicarboxylic acid l-aspartic acid and N-alkylated amino acids (peptoid building blocks, e.g., NPhe-OH 9). The latter can be used in the preparation of dipeptidomimetics.
- Van Leeuwen,Quaedflieg,Broxterman,Milhajlovic,Liskamp
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p. 653 - 656
(2007/10/03)
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- A solvent-free method for substituted imidazolidin-4-ones synthesis
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A new method of the solvent-free synthesis of substituted imidazolidin-4-ones is described. The method is developed for microwave-assisted solvent-free conditions and compared with classical thermally initiated solvent-free conditions. In both cases the reaction proceeds with good yields. However, the reaction under microwave conditions is accelerated six-times. Thermal effect of the microwaves is observed.
- Pospí?il, Ji?í,Potá?ek, Milan
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p. 1165 - 1173
(2007/10/03)
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