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排序方式: 共有193条查询结果,搜索用时 218 毫秒
71.
V. I. Tararov C. Orizu N. S. Ikonnikov V. S. Larichev M. A. Moscalenko L. V. Yashkina M. North Yu. N. Belokon 《Russian Chemical Bulletin》1999,48(6):1128-1130
The enantiomeric purity (ee) of the addition product of Me3SiCN to PhCHO at ∼20 °C catalyzed by chiral TiIV complexes, which were preparedin situ from Ti(OPri)4 and the Schiff bases (condensation products of substituted salicylaldehydes with (1R, 2R)-1,2-diaminocyclohexane), was, on the average, 20–30% lower than that achieved at −80 °C. The substituents at position 5
of 3-tert-butylsalicylaldehyde exert only the steric effect. It was shown that the stereochemical result of the reaction is controlled
by the stage which involves the formation of the C−C bond rather than the transfer of the Me3Si group.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1139–1141, June, 1999. 相似文献
72.
73.
YuriN. Belokon Paola Carta AndreyV. Gutnov Viktor Maleev MargaritaA. Moskalenko LidiaV. Yashkina NicolaiS. Ikonnikov NikolaiV. Voskoboev ViktorN. Khrustalev Michael North 《Helvetica chimica acta》2002,85(10):3301-3312
The utility of the chiral [Ti(μ‐O)(salen)]2 complexes (R)‐ and (S)‐ 1 (H2salen was prepared from (R,R)‐ or (S,S)‐cyclohexane‐1,2‐diamine and 3,5‐di(tert‐butyl)‐2‐hydroxybenzaldehyde) as catalysts for the asymmetric addition of KCN and Ac2O to aldehydes to produce O‐acetylcyanohydrins was investigated. It was shown that the complexes were active at a substrate/catalyst ratio of 100 : 1 and produced the O‐protected cyanohydrins with ee in the range of 60–92% at −40°. Other complexes, [Ti2(AcO)2(μ‐O)(salen)2] ((R)‐ 4 ) and [Ti(CF3COO)2(salen)] ((R)‐ 5 ), were prepared from (R)‐ 1 by treatment with different amounts of Ac2O and (CF3CO)2O, and their catalytic activities were tested under the same conditions. The efficiency of (R)‐ 4 was found to be even greater than that of (R)‐ 1 , whereas (R)‐ 5 was inactive. The synthesis of the corresponding salen complexes of VIV and VV, [V(O)(salen)] ((R)‐ 2 ) and [V(O)(salen)(H2O)] [S(O)3OEt] ((R)‐ 3 ), was elaborated, and their X‐ray crystal structures were determined. The efficiency of (R)‐ 3 was sufficient to produce O‐acetyl derivatives of aromatic cyanohydrins with ee in the range of 80–91% at −40°. 相似文献
74.
Time-resolved frequency-modulation spectroscopy is shown to be an effective method for measuring the rates of gas-phase reactions. As an example, the rate constant for the reaction of CN with C2H4 at 298 K is measured to be 2.5 ± 0.2 × 10−10 cm3s−1, in good agreement with other literature values. The efficiency and sensitivity of this technique will be of interest to the chemical kineticist. © 1997 John Wiley & Sons, Inc. 相似文献
75.
Javier Martínez Dr. José A. Castro‐Osma Amy Earlam Dr. Carlos Alonso‐Moreno Prof. Antonio Otero Dr. Agustín Lara‐Sánchez Prof. Michael North Dr. Antonio Rodríguez‐Diéguez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9850-9862
New aluminium scorpionate based complexes have been prepared and used for the synthesis of cyclic carbonates from epoxides and carbon dioxide. Bimetallic aluminium(heteroscorpionate) complexes 9 – 14 were synthesised in very high yields. The single‐crystal X‐ray structures of 12 and 13 confirm an asymmetric κ2‐NO‐μ‐O arrangement in a dinuclear molecular disposition. These bimetallic aluminium complexes were investigated as catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide in the presence of ammonium salts. Under the optimal reaction conditions, complex 9 in combination with tetrabutylammonium bromide acts as a very efficient catalyst system for the conversion of both monosubstituted and internal epoxides into the corresponding cyclic carbonates showing broad substrate scope. Complex 9 and tetrabutylammonium bromide is the second most efficient aluminium‐based catalyst system for the reaction of internal epoxides with carbon dioxide. A kinetic study has been carried out and showed that the reactions were first order in complex 9 and tetrabutylammonium bromide concentrations. Based on the kinetic study, a catalytic cycle is proposed. 相似文献
76.
77.
The connection between the K-quantum number and product correlations in the barrierless unimolecular dissociation of symmetric-top molecules is explored to establish a qualitative diagnostic for the treatment of the K-rotor dynamics in unimolecular reaction theory. We find that fragment scalar and vector correlations can provide guidance in this matter, and the photodissociation dynamics of thermal NCNO to form CN and NO at several dissociation wavelengths are presented to demonstrate the utility of this approach. The "goodness" of the K-quantum number can be related to the amount of energy in the conserved vibrational modes at the inner transition state. On the basis of measured correlated vibrational distributions, the K-quantum number is found to be approximately conserved at the inner transition state for the photodissociation of NCNO at 514, 520, and 526 nm. The methodology, involving a comparison of product distributions from the photodissociation of jet and thermal ensembles at identical wavelengths, is general and may be applied to previously studied systems that dissociate along barrierless potential energy surfaces, CF(3)NO and CH(2)CO. In addition, vector correlations serve as a means to probe the K-mixing at the outer transition state, and measured v-j correlations in the photodissociation of thermal NCNO are presented. 相似文献
78.
The reaction of the formylfuran with maleic anhydride and N-mthylmaleimide is reported as the key step in the synthesis of novel 10-oxa-9,11-ethano-PGH1 analogues. 相似文献
79.
80.
Non-racemic cyanohydrin acetates are readily available from aldehydes and potassium cyanide/acetic anhydride by use of bimetallic titanium (salen) catalyst 1. Treatment of the cyanohydrin acetates with a platinum(II) phosphinito catalyst 3 under neutral conditions results in chemoselective hydrolysis to the corresponding α-acetoxy amides in a racemization free process. 相似文献