共查询到20条相似文献,搜索用时 0 毫秒
1.
Noureddine Khiar Cristina S Araújo Eleuterio AlvarezInmaculada Fernández 《Tetrahedron letters》2003,44(16):3401-3404
A new divergent design for the synthesis of optically pure bis-thioglycoside type I is reported. In only two steps a common chiral intermediate with up to eight free alcohols: two primary and six secondary is obtained. From this common intermediate a large number of ligands can be synthesized. A positional scanning like strategy has permitted the rapid discovery of an efficient catalyst for the palladium-catalyzed asymmetric allylation of malonate. Dynamic NMR spectroscopy of a Pd(II) complex has shown that there is an efficient stereochemical control of the sulfur configuration upon coordination to the palladium. 相似文献
2.
3.
Jean-Claude KizirianJean-Claude Caille Alexandre Alexakis 《Tetrahedron letters》2003,44(49):8893-8895
New chiral diamines were prepared, based on the cyclohexane diamine core. The two different substituents on each nitrogen allow this heteroatom to become a stereogenic center upon chelation with a metal, such as lithium. The enantioselective addition of MeLi to imines, with ee's up to 68%, illustrates the validity of this concept. 相似文献
4.
Julen MendizabalPedro de March Josep RecasensAlbert Virgili Ángel Álvarez-LarenaJosé Elguero Ibon Alkorta 《Tetrahedron》2012,68(47):9645-9651
Herein we report a protocol for the enantioselective synthesis of the three stereoisomers of 1,1′-(1,1′-binaphthalene-2,2′-diyl)bis(2,2,2-trifluoroethanol) and their characterization. These compounds, that combine axial and central chirality, might present interesting properties for enantiorecognition. Different reduction processes were applied to racemic and enantiopure 1,1′-(1,1′-binaphthalene-2,2′-diyl)bis(2,2,2-trifluoroethanone) allowing the isolation of the corresponding ketols, 2,2,2-trifluoro-1-[2′-(2,2,2-trifluoro-1-hydroxyethyl)-1,1′-binaphthalen-2-yl]ethanone, and the named diols. 相似文献
5.
A series of new C2-symmetric chiral diamides were synthesized from l-tryptophan and used as chiral ligands chelated with Cu(II) in enantioselective Henry reactions. Ligand 4a with CuCl2·2H2O (5%) showed effective catalytic efficiency in Henry reaction. High yields (up to 99%) and excellent enantioselectivities (up to 98%) were achieved for both aromatic and aliphatic aldehyde substrates. 相似文献
6.
Lianhong Xu 《Tetrahedron letters》2009,50(5):552-2204
A novel and efficient method for synthesis of (R,R)- and (S,S)-C2-symmetric 1,4-diamines was established. The key steps are a combination of Pinacol Coupling and Corey-Winter olefination. 相似文献
7.
《Tetrahedron》2004,60(2):415-427
Several o-dibenzylic diols were prepared reacting organometallics with o-phthalaldehyde at room temperature in ether. The identity of the meso and C2-symmetrical (d,l) isomers as well as their ratio were determined by chiral gas chromatography. The meso and C2 (racemic) stereoisomeric diols were easily separated by flash chromatography on silica gel. A set of 18 α,β-unsaturated acetals were then prepared reacting those, as well as commercially available 1,2, 1,3 and 1,4 diols, with the corresponding methylacetals in acidic medium. A trans-acetalisation procedure adapted to the cases of fragile allylic alcohols or unfavorable 1,6 diols-derived dioxonanes based on a Dean-Stark trapping of methanol was also employed. 相似文献
8.
The first 9- and 11-membered cis and trans C2-symmetric benzimidazol-2-ylidene palladium(II) complexes based on a trans-2,2-dimethyl-1,3-dioxalane backbone were synthesised and the configuration of the complexes was elucidated via NMR and X-ray crystallography. 相似文献
9.
A novel one-pot reductive amination of ketones using the combination Ti(OiPr)4/H2/Pd-C is reported. This practical procedure does not require any solvent, and affords C2-symmetrical secondary amines in high yields and excellent diastereoselectivities. 相似文献
10.
A rapid and efficient method for preparation of C2-symmetrical 1,3,5-triazine polycarboxylate ligands was developed. The reactions included either selective mono- or di-substitution of 2,4,6-trichloro-1,3,5-triazine with various nucleophiles containing carboxyl group(s), followed by nucleophilic displacement of the remained chloride(s) in aqueous media under microwave irradiation. Novel C2-symmetrical tripodal ligands were afforded in good yields and purities under short reaction time with simple work-up, which are potentially useful as structural directing units in metal-organic frameworks. 相似文献
11.
Taichi Kano 《Tetrahedron letters》2006,47(48):8467-8469
The anti-selective direct asymmetric Mannich reaction was found to be efficiently catalyzed by the novel pyrrolidine-based amino sulfonamide (R,R)-2 prepared from l-tartaric acid. 相似文献
12.
P. Veeraraghavan Ramachandran Debanjan Biswas Marek P. Krzeminski Guang-Ming Chen 《Tetrahedron letters》2010,51(2):332-336
An enantioselective synthesis of C2-symmetric bis-homoallylic aromatic and heteroaromatic diamines in 54-89% yields, in 73-94% de and ?98% ee has been achieved via the allylboration of the corresponding N,N′-bis(trimethylsilyl)dialdimines and N,N′-bis(diisobutylalumino)dialdimines with B-allyldiisopinocampheylborane in the presence of methanol, followed by alkaline hydrogen peroxide workup. One-pot synthesis of stable N,N′-bis(benzaldimine-triethylborane) complexes and subsequent allylboration to afford benzene diamines is also described. 相似文献
13.
A chiral organocatalyst was successfully entrapped by montmorillonite clay using the cation-exchange method. The mont-entrapped organocatalyst acted as a highly efficient and reusable heterogeneous catalyst for the asymmetric Diels-Alder reaction, without loss of its initial activity. 相似文献
14.
C-Galactosyl and C-ribosyl β-amino acids were prepared by one-pot InCl3-catalyzed Mannich-type three-component condensation (3CC) by combining the corresponding formyl C-glycoside, p-methoxybenzyl amine, and a ketene silyl acetal. In each case the reaction was highly stereoselective and afforded only one single product in good to excellent yields. 相似文献
15.
16.
Fang Fang 《Tetrahedron》2010,66(20):3593-6201
A novel class of atropos dibridged biphenyl phosphoramidites bearing a D2-symmetric biphenyl backbone was prepared and applied as chiral ligands in the copper-catalyzed allylic alkylation with Grignard reagent. The alkylation products were obtained in quantitative yields with high regioselectivities up to 94:6 of SN2′/SN2 ratio and enantiomeric excesses up to 91.1% for SN2′ products. The unique D2-symmetric backbone ligands have the advantages of easy preparation and sufficient reusability of their key intermediates from the undesired isomers. 相似文献
17.
Johan F. Billing 《Tetrahedron letters》2005,46(6):991-993
A C3-symmetric macrocycle with alternating sugar amino acid and tyrosine residues was synthesized in seven steps from tyrosine tert-butyl ester and a sugar amino acid precursor derived from D-glucosamine. An Fmoc-protected D-glucosamine derivative was oxidized at C-6 to give the sugar amino acid, which was immediately coupled to tyrosine tert-butyl ester to produce an orthogonally protected building block. This building block was subsequently elongated to the trimer via the dimer, and finally cyclized to give the C3-symmetric macrocycle. 相似文献
18.
La2Mo2O9 ceramics have been prepared from freeze-dried precursors and their properties compared to those of lantanum molybdate obtained by conventional solid state (SS) reaction. All materials have been characterized by X-ray diffraction, scanning electron microscopy and thermal analysis (TGA/DTA/DSC and dilatometry) to characterize the phase formation and phase transition. When the freeze-dried method was applied, the synthesis temperature required to obtain dense samples was much lower than that for powders obtained by SS reaction. The morphology and structure of the oxide particle are significantly dependent on the synthesis method. The grain size is smaller, whereas the density of sintered pellets is higher for the freeze-dried precursor powder when compared with the SS reaction method. Impedance spectroscopy was used to measure the electrical conductivity of La2Mo2O9 from 548 to 1123 K, in air, and to characterize the blocking effects of grain boundaries. 相似文献
19.
Optically pure C2-symmetric diols have been synthesized with moderate yields in a straightforward manner, and are used as catalysts in the enantioselective alkylation of aromatic aldehydes with diethylzinc. The addition of diethylzinc to benzaldehyde and sterically hindered 1-naphthaldehyde was achieved with excellent enantioselectivities (97–99% ee) under catalysis with (1R,2R)-1,2-bis(3,5-dibromophenyl)-ethane-1,2-diol and (1R,2R)-1,2-bis(3,5-diphenylphenyl)-ethane-1,2-diol. 相似文献