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611.
Sharan K. BagalStephen G. Davies Ai M. FletcherJames A. Lee Paul M. RobertsPhilip M. Scott James E. Thomson 《Tetrahedron letters》2011,52(17):2216-2220
Diastereoselective conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to tert-butyl sorbate and subsequent chemo- and diastereoselective ammonium-directed olefinic oxidation of the resultant conjugate addition product {tert-butyl (3S,αR)-3-[N-benzyl-N-(α-methylbenzyl)amino]hex-4-ene} have been used as the key steps in a concise and highly selective asymmetric synthesis of the 2,3,6-trideoxy-3-aminohexose l-acosamine. This sequence of two chemical operations allows rapid assembly of the molecular architecture and facilitates the de novo asymmetric synthesis of methyl N,O-diacetyl-α-l-acosaminide in only 7 steps from commercially available sorbic acid in 15% overall yield. 相似文献
612.
Tetsuhiro NemotoKazumichi Obuchi Shinji TamuraTakashi Fukuyama Yasumasa Hamada 《Tetrahedron letters》2011,52(9):987-991
Novel chiral hydrogen bond donor catalysts based on a 4,5-diamino-9,9′-dimethylxanthene skeleton were designed and synthesized. Among the phenylurea-amide hybrid molecules prepared from various natural/unnatural chiral amino acids, the phenylalanine-derived catalyst, and the proline-derived catalyst were successfully applied to enantioselective conjugate addition of 1,3-dicarbonyl compounds to nitroalkenes. Using 2-acetylcyclopentanone and 2-methoxycarbonylcyclopentanone as prochiral nucleophiles, asymmetric conjugate addition to β-aryl nitroalkenes proceeded with good diastereoselectivity to provide the corresponding products bearing an all-carbon quaternary stereocenter in excellent yield with up to 95% ee. 相似文献
613.
Andrew Dahao Yeung 《Journal of organometallic chemistry》2011,696(1):112-117
Three cis-chelating di-N-heterocyclic carbene palladium(II) complexes [PdX2(diNHC)] (X = I, 1; X = SCN, 2; X = CF3CO2, 3) bearing different anionic co-ligands were synthesized and fully characterized. A comparison of their catalytic activities in the Mizoroki-Heck reaction and conjugate addition of arylboronic acids to cyclic enones revealed increasing efficiency in the order SCN− < I− < CF3CO2−. The di(trifluoroacetato) complex 3 showed the best activity in both transformations highlighting the importance of co-ligands effects in catalysis. In addition, the molecular structure of an unusual poly-heteronuclear complex salt 4 is reported, which has been isolated as a byproduct in the synthesis of complex 3. 相似文献
614.
本文通过结合牛顿法与PRP共轭梯度法提出一修正PRP方法,新方法中包含了二阶导数信息,在适当的假设下算法全局收敛,数值算例表明了算法的有效性. 相似文献
615.
616.
Petr Vašek 《Supramolecular chemistry》2013,25(7):529-536
Interactions of a new porphyrin–β-cyclodextrin conjugate (1) with a number of aromatic compounds have been studied after covalent immobilization of 1 onto a solid matrix of 3-aminopropylated silica particles. The effects of both porphyrin and β-cyclodextrin moieties on interactions with achiral aromatic compounds were studied and the influence of the achiral porphyrin spacer on chiral recognition of binaphthyl derivatives by the β-cyclodextrin moiety of 1 is discussed. 相似文献
617.
The aim of the paper was to investigate the effect of ultrasonic emulsification treatment on the fabrication mechanism and stability of the emulsion. The covalent conjugate made with rice bran protein hydrolysate (RBPH) and ferulic acid (FA) was used as the emulsifier. The effects of high intensity ultrasound (HIU) power with different level (0 W, 150 W, 300 W, 450 W and 600 W) on the stability of emulsion were evaluated. The results showed that ultrasonic emulsification can significantly improve the stability of the emulsions (p < 0.05). The emulsion gained better stability and emulsifying property at 300 W. It was able to fabricate emulsion with smaller particle size, more uniform distribution and higher interfacial protein content. It was confirmed by fluorescent microscopy and cryo-scanning electron microscopy (cryo-SEM) furtherly. And it was also proved that the emulsion treated by proper HIU treatment at 300 W had better storage stability. Excessive HIU treatment (450 W, 600 W) had negative effects on the stability of emulsion. The stability of emulsion (300 W) against different environmental stresses was further explored, which established a theoretical basis for the industrial application of emulsion in food industry. 相似文献
618.
Although nitrogen-containing heterocycles and sulfonamides both play crucial roles in the chemical and pharmaceutical industries, surprisingly little research exists that examines the bifunctional N-(2-(pyridin-2-yl)ethyl)sulfonamide scaffold for any potential applications. Retrosynthetic analysis indicates that this skeleton would be well suited for a conjugate addition reaction. However, the ability of 2-vinylpyridine to behave as an acceptor, and of sulfonamides to behave as donors, has very limited literature precedent, and thus required some preliminary investigations into their mutual reactivity. Herein outlines our laboratory's discovery of a novel and efficient solvent-free 1,4-aza-conjugate addition reaction between sulfonamides and 2-vinylpyridines that provides expedient access to various N-(2-(pyridin-2-yl)ethyl)sulfonamide derivatives. The products, possessing multiple sites of Brønsted acidity and basicity in close proximity, could display a wide array of valuable host–guest properties and should thus be investigated for potent pharmaceutical or agrochemical properties.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
619.
Shin-ichi Hirashima Kosuke Nakashima Yuki Fujino Ryoga Arai Takaaki Sakai Masahiro Kawada Yuji Koseki Miho Murahashi Norihiro Tada Akichika Itoh Tsuyoshi Miura 《Tetrahedron letters》2014
A diaminomethylenemalononitrile organocatalyst with a cinchona motif efficiently promotes the enantioselective conjugate addition of acetylacetone to various nitroalkenes to yield the corresponding addition products in high to excellent yields with up to 89% ee. 相似文献
620.
Brad P. Morgan 《Journal of organometallic chemistry》2008,693(1):11-16
A rhodium complex [ClRh(CO)(L1)] featuring a wide bite angle diphosphine ligand (L1 = 1,3-bis(2-diphenylphosphinomethylphenyl)benzene) has been synthesized and structurally characterized. L1 supports a bite angle (P-M-P angle, β) of 171.4° in the trans-square planar complex. L1 was tested in Rh-catalyzed 1,4-addition reactions of arylboronic acids (six examples) to α,β-unsaturated ketones (five examples). In mixed aqueous/cyclohexane solution at 60 °C, addition reactions proceed in up to quantitative yield with a 1:1 arylboronic acid/enone ratio. Yields as high as 77% can be acquired even when one of the coupling partners is sterically encumbered 2,4,6-trimethylphenylboronic acid. 相似文献