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91.
Gyrgy Keglevich Nra Zsuzsa Kiss Dra K. Menyhrd Andrs Fehrvri Istvn Csontos 《Heteroatom Chemistry》2012,23(2):171-178
The Kabachnik–Fields reaction of benzaldehyde, cyclohexylamine, and dimethyl phosphite carried out at 80°C in acetonitrile takes place via an imine (PhCN cHex) intermediate, as the monitoring by in situ Fourier transform IR spectroscopy suggested. The corresponding α‐hydroxyphosphonate was also formed in a quantity of 13% that was not converted to α‐aminophosphonate under the conditions applied. The outcome was similar to the Kabachnik–Fields reaction with diethyl phosphite as the P‐component. Molecular modeling and subsequent DFT calculations carried out under solventless conditions supported the experimental results and indicated the formation of a high number of ideally positioned H bonds as the key determinant for the conformation of the starting, intermediate, and product states. The relative energies of the possible intermediates were in accord with the observation that the formation of the α‐hydroxyphosphonate is a “dead‐end” route. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:171–178, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20767 相似文献
92.
Both the reaction enthalpies and enthalpies of activation obtained by high‐level quantum chemical calculations were against the direct amidation of phosphinic acids under traditional thermal conditions. However, the amidations, not expected to proceed on the basis of the endothermicity and the significantly high enthalpies of activation, did take place under microwave (MW) conditions in 30–36% conversions. As a comparison, the direct esterifications of phosphinic acids that are thermoneutral and have higher enthalpies of activation were quite efficient under MW conditions. The outcome of the MW‐assisted amidation is the balance of two effects. The local overheating effect could overcome the barrier meant by the enthalpy of activation, but the endothermicity works against this. Comparison of the results of the syntheses and the energetics calculated for the esterification and amidation of phosphinic acids enabled us to draw more general conclusions on the scope and limitation of the use of MW irradiation in organic syntheses. The traditional amidation of phosphinic acids via the phosphinic chloride intermediate gave the products in much better yields. © 2013 Wiley Periodicals, Inc. Heteroatom Chem 24:91–99, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21068 相似文献
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Numerous substituted α‐aminophosphinates were synthesized by addition of alkyl and phenyl H‐phosphinates to aromatic imines and characterized. Modest diastereoselectivity was observed in the reaction. The size of the substituents exerts a small effect on the diastereoselectivity of P C bond formation. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:235–240, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10133 相似文献
96.
Enik Szkely Gizella Csire Bettina Dina Balogh Judit Zsuzsa Erdei Judit Mria Kirly Judit Kocsi Júlia Pinkczy Katalin Vrnagy 《Molecules (Basel, Switzerland)》2022,27(11)
The systematic studies of copper(II), nickel(II) and zinc(II) ion complexes of protected multihistidine peptides containing amino acids with different side chains (Ac-SarHAH-NH2, Ac-HADH-NH2, Ac-HDAH-NH2, Ac-HXHYH-NH2 X, Y = A, F, D or K, Ac-HXHAHXH-NH2, X = F or D) have provided information about the metal ion and protein interaction and have made it possible to draw conclusions regarding general trends in the coordination of metal complexes of multihistidine peptides. The stability of the metal complexes significantly depends on the position of the histidines and amino acids, which are present in the neighbourhood of the histidine amino acids as well. The most significant effect was observed on peptides containing aspartic acid or phenylalanine. The redox parameters of complexes, however, depend on the number and position of histidines, and the other side chain donor atoms have practically no effect on the electrochemical properties of imidazole-coordinated species. However, the presence of aspartic acid side chains results in a more distorted geometry of amide-coordinated species and increases the reducibility of these complexes. 相似文献
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A stability theorem says that a nearly extremal object can be obtained from an extremal one by “small changes”. In this paper, we study the relation of sets having few 0-secants and blocking sets. 相似文献
99.
Irreproducibilities in the measurements of isotopic abundance in 15N labelled glycine have been related to the complex nature of chemical processes occurring during the evaporation of glycine prior to ionization. 相似文献
100.