排序方式: 共有112条查询结果,搜索用时 312 毫秒
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Gual A Castillón S Pàmies O Diéguez M Claver C 《Dalton transactions (Cambridge, England : 2003)》2011,40(12):2852-2860
A series of C(1)-symmetrical 1,3-diphosphite ligands with a furanoside backbone have been applied in the Pd-catalysed asymmetric allylic alkylation of mono- and disubstituted linear substrates. These diphosphite ligands were designed by selective modification of the successful diphosphite ligand L1a with the 6-deoxy-1,2-O-isopropylidene-glucofuranose backbone in order to study the effect of the ligand structure on the catalytic performance. The effect of the solvent, the substrate/metal ratio and ligand/metal ratio were also investigated. The results in the Pd-allylic alkylation of rac-1,3-diphenyl-3-acetoxyprop-1-ene showed that the ligand structure and the reaction conditions had a considerable effect on enantioselectivity and on the kinetics of the reaction producing the kinetic resolution of the substrate. The alkylated product 2 was therefore obtained in 95% ee at 53% conversion and the enantiopure substrate 1 was recovered in 99.9% ee. Furthermore, the effect of the ligand structure and solvent were also observed in the Pd-allylic alkylation of monosubstituted 1-phenyl-3-acetoxyprop-1-ene. The use of a pro-chiral nucleophile was also explored in this reaction leading to excellent regioselectivities but moderate enantioselectivities. Finally, in order to determine how the ligand structure affected the chiral pocket of the Pd-π-allyl intermediates, the complexes [Pd(η(3)-C(15)H(13))(L)]PF(6), where L = L1a, L5-L8a, were synthesised and characterised by NMR spectroscopy. 相似文献
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Crozet D McKay D Bijani C Gual A Godard C Claver C Maron L Urrutigoïty M Kalck P 《Dalton transactions (Cambridge, England : 2003)》2012,41(12):3369-3373
Reaction of [Rh(CO)(2){(R,R)-Ph-BPE}][BF(4)] 1 under 7 bar H(2) provides the dihydride [Rh(H)(2)(CO)(2){(R,R)-Ph-BPE}][BF(4)] 3, which reacts with the neutral hydride [Rh(H)(CO){(R,R)-Ph-BPE}] 2 arising from 3 in THF. The resulting complex is the dimeric monocationic Rh((I))-Rh((III)) complex [Rh(H)(2)(CO)(2){(R,R)-Ph-BPE}][BF(4)] 4. 相似文献
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Mercedes Iriarte Antonio Hernanz Juan F. Ruiz‐Lpez Santiago Martín 《Journal of Raman spectroscopy : JRS》2013,44(11):1557-1562
The composition of the materials present in prehistoric paintings discovered on the walls of the Abrigo Remacha rock shelter (Villaseca, Segovia, Spain) has been characterised by micro‐Raman spectroscopy. In addition, scanning electron microscopy and energy dispersive X‐ray microanalysis have been used as auxiliary techniques. The results show that haematite (α‐Fe2O3) is the main component of the red pigment. Amorphous carbon and paracoquimbite (Fe2(SO4)3.9H2O) have been detected in the bluish black pigment used in a significant bi‐colour pictograph. This is the first time that this mineral has been discovered in a prehistoric painting. Accretions of whewellite and weddellite form crusts covering most of the painting panel. Different carbonates are the main components of the rocky substrate. The detection of gypsum on the surface of the panel is associated to the flaking process that is affecting the painting panel. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Christian A. Iriarte CapaccioOscar Varela 《Tetrahedron letters》2003,44(21):4023-4026
The influence of such Lewis acids as Et2O·BF3, ZnCl2, SnCl4 and TiCl4 on the stereochemical course of the Diels-Alder cycloadditions of sugar-derived (2S)-alkoxydihydropyranones was studied. The first two catalysts promoted the addition of dienes to give (3S,4aR,8aS)-3-alkoxy-4a,5,8,8a-tetrahydro-2-benzopyran-4-ones, and their concentration had almost no effect on the stereochemistry of the reaction. In contrast, the concentration of SnCl4 and TiCl4 had a remarkable influence on the selectivity, and even facial stereoselection reversal has been observed. These results may be ascribed to chelate complexation of the Lewis acid with the carbonyl and the vicinal alkoxy group of the dihydropyranone. 相似文献
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Ana G. Iriarte Edgardo H. Cutin Carlos O. Della Vdova 《Journal of Molecular Structure》2006,800(1-3):154-157
The infrared and Raman spectra of 2-chloro-2,2-difluoroacetamide (ClF2CC(O)NH2) have been recorded and analyzed with the complement of results derived from computational chemistry calculations. Thus, delocalization effects and stabilization energies have been computed for the title molecule and a complete assignment has been also proposed. 13C, 19F and 1H NMR chemical shifts and coupling constants have been also measured for this substance. 相似文献
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Spectroscopic separation of 13C NMR spectra of complex isomeric mixtures by the CSSF‐TOCSY‐INEPT experiment 下载免费PDF全文
Lu Yang Aitor Moreno Wolfgang Fieber Robert Brauchli Horst Sommer 《Magnetic resonance in chemistry : MRC》2015,53(4):304-308
Isomeric mixtures from synthetic or natural origins can pose fundamental challenges for their chromatographic separation and spectroscopic identification. A novel 1D selective NMR experiment, chemical shift selective filter (CSSF)‐TOCSY‐INEPT, is presented that allows the extraction of 13C NMR subspectra of discrete isomers in complex mixtures without physical separation. This is achieved via CSS excitation of proton signals in the 1H NMR mixture spectrum, propagation of the selectivity by polarization transfer within coupled 1H spins, and subsequent relaying of the magnetization from 1H to 13C by direct INEPT transfer to generate 13C NMR subspectra. Simple consolidation of the subspectra yields 13C NMR spectra for individual isomers. Alternatively, CSSF‐INEPT with heteronuclear long‐range transfer can correlate the isolated networks of coupled spins and therefore facilitate the reconstruction of the 13C NMR spectra for isomers containing multiple spin systems. A proof‐of‐principle validation of the CSSF‐TOCSY‐INEPT experiment is demonstrated on three mixtures with different spectral and structural complexities. The results show that CSSF‐TOCSY‐INEPT is a versatile, powerful tool for deconvoluting isomeric mixtures within the NMR tube with unprecedented resolution and offers unique, unambiguous spectral information for structure elucidation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Jiménez J Landa A Lizarraga A Maestro M Mielgo A Oiarbide M Velilla I Palomo C 《The Journal of organic chemistry》2012,77(1):747-753
The catalytic direct α-alkylation of aldehydes with 2-(bromomethyl)acrylates has been accomplished, giving rise to α-branched and functionalized aldehydes of high diastereo- and enantiopurity. The influence of the nature of the ester group of the acrylates in reaction stereoselectivity and especially in reactivity is investigated. Optimum conditions implicate the use of phenyl acrylates in conjunction with organocatalyst 8. Application of thus obtained adducts in synthesis is illustrated with a concise stereocontrolled preparation of trisubstituted cyclopentenes. 相似文献