共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
《Tetrahedron: Asymmetry》2003,14(18):2771-2774
A clear positive nonlinear effect of the enantiopurity of ligand 1 on the product ee was observed in the enantioselective 1,4-conjugate addition of Et2Zn to chalcone. The experimental data of nonlinear effect meet Kagan's ML2 model. 相似文献
3.
4.
A mesoporous silica FSM-16 was found to be a recyclable oxidizing promoter of arylmethyl bromides for the preparation the corresponding carboxylic acids, aldehydes, or ketones under photoirradiation conditions. 相似文献
5.
The 1,4-addition of thio nucleophiles to chiro-inositols containing a cinnamyl Michael acceptor proceeded with excellent diastereochemical induction and good yields. Cleavage of the inositol auxiliary provides beta-thio hydrocinnamic acids in >99% ee's. 相似文献
6.
Anirban Mondal Sudipto Bhowmick Ayndrila Ghosh Tanmoy Chanda Kartick C. Bhowmick 《Tetrahedron: Asymmetry》2017,28(7):849-875
Asymmetric Michael addition reactions or 1,4-conjugate addition reactions are considered to be the fundamental C–C bond-forming reaction for the construction of chiral β-nitro, β-carbonyl and several other important structural motifs in organic synthesis. After the development of many chiral metal complexes as catalysts, a tremendous growth in the design and applications of variety of new chiral organocatalysts for asymmetric 1,4-conjugate addition reactions has been witnessed over the last two decades. Initially, asymmetric organocatalysis has been performed in organic solvents, but gradually performing the same catalysis in aqueous and semi-aqueous media became a necessity due to environmental aspects as well as to achieve better reactivity and selectivity. The structural and functional diversity of the chiral organocatalysts derived from natural and synthetic sources utilized differently the water either as the sole solvent, co-solvent or additive for optimising their best performances. In the present review, we discuss a detailed and comprehensive report on the advancement in the field of asymmetric organocatalytic 1,4-conjugate addition reactions in aqueous and semi-aqueous media. 相似文献
7.
《Tetrahedron: Asymmetry》2006,17(1):136-141
The copper-catalyzed enantioselective 1,4-conjugate addition of diethylzinc to chalcones was investigated in the presence of a catalytic amount of N,P-ferrocenyl ligands with central and planar chirality under mild conditions (0 °C→rt). It was found that chalcones with ortho-substituents (from ortho-substituted benzaldehydes and acetophenone/substituted acetophenones) led to a dramatic improvement in the enantioselectivities. The (R)- and (S)-antipodes of the addition reaction were obtained with up to 92% ee after this transformation. 相似文献
8.
The rhodium-catalyzed reaction of Sb-aryl-1,5-azastibocines with alpha,beta-unsaturated ketones and esters is described. Exclusive formation of 1,4-conjugate adduct was achieved in aqueous NMP (N-methyl-2-pyrrolidinone) in the presence of 5 mol% of [RhCl(cod)](2), and no formation of Heck adduct was observed in this condition. Reactions with various enones and enoates were also demonstrated to prove generality of the 1,4-conjugate addition. 相似文献
9.
10.
11.
The asymmetric alkylation with diethylzinc of five heterocyclic aldehydes and benzaldehyde (for comparison) has been studied in the presence of two optically active amino alcohols: (S)-2-amino-1-butanol (AB) and (1S,2R)-N,N-dibutylnorephedrine (DBNE). A number of chiral (hetero)aromatic secondary alcohols were synthesized in high yields (95–98%) with enantioselectivity up to 92% enantiomeric excess (ee) in the presence of DBNE catalyst. Optically active thienyl and 4-pyridyl derivatives were prepared for the first time by catalytic asymmetric alkylation. The influence of the amount of DBNE on the enantioselectivity was investigated. In contrast to benzaldehyde, 2-furan- and 2-thiophene-carbaldehydes, in the case of 3- and 4-pyridinecarbaldehydes the ee values depend directly on the catalyst concentration. © 1998 John Wiley & Sons, Ltd. 相似文献
12.
G. Yu. Ishmuratov E. R. Latypova P. Ya. Kharisov R. R. Muslukhov A. A. Bannova R. F. Talipov G. A. Tolstikov 《Russian Journal of Organic Chemistry》2008,44(5):652-656
(R)-4-Menthenone compared with common cyclic enones exhibits considerably lower reactivity in 1,4-conjugate addition of organometallic reagents, is inert in Michael reactions and pyrazoline formation evidently due both to the distorted polarization in the enone system and to steric hindrances from the α-isopropyl group in the cyclohexene ring. 相似文献
13.
Hicham ZilaoutAdri van den Hoogenband Jelle de VriesJos H.M. Lange Jan Willem Terpstra 《Tetrahedron letters》2011,52(45):5934-5939
An unprecedented rhodium-catalyzed 1,4-conjugate addition of arylboronic acids with ethenesulfonamides resulting in the corresponding 2-arylethanesulfonamides is described. The amino substituent, the applied arylboronic acid, the type of Rh-catalyst, and the experimental conditions all affected the reaction outcome. 相似文献
14.
One of the most efficient and reliable approaches to construct C–C bonds involves the conjugate addition of carbon nucleophiles to electron-deficient ketones. Yet, 1,6-conjugate additions of extended conjugated systems largely remain underexplored due to difficulties in controlling the regioselectivity. Herein, we report umpolung aldehydes as carbanion equivalents for highly regioselective 1,6-conjugate addition reactions to unsaturated ketones, with preliminary studies of the enantioselective variant. The synergy of ruthenium(ii) catalyst and electron-rich, bidentate phosphine ligand is essential for the reactivity and selectivity under mild reaction conditions.Highly regioselective 1,6-conjugate addition was developed using hydrazone as carbanion equivalent catalyzed by ruthenium under mild conditions. 相似文献
15.
Isoleucine-catalyzed direct enantioselective aldol additions between enolizable aldehydes are reported. Intermediate acetal structures dictate the configurative outcome and were supported by a hydrogen bond. This direct isoleucine-catalyzed aldol addition represents a welcome complement to both proline- and histidine-catalyzed aldol additions of enolizable aldehydes. 相似文献
16.
The 1,4-addition of diethylzinc and dimethylzinc to 5,6-hydro-2H-pyran-2-one using new chiral diphosphite-copper catalysts gave products in up to 98% ee. 相似文献
17.
18.
《Tetrahedron: Asymmetry》2000,11(14):2971-2979
Enantioselective addition reactions of diethylzinc to aldehydes were performed by catalytic reactions with chiral 1,4-aminoalcohols. Optically active 1,4-aminoalcohols were synthesized from (+)-camphor and (−)-fenchone through four steps involving iodine-mediated lactonization of 3-hydroxy acids. 相似文献
19.
《Tetrahedron: Asymmetry》2006,17(1):107-111
A variety of enantiopure proline derived pyrrolidinium (HX)n salts have been found to catalyse the 1,4-conjugate addition of N-methylpyrrole to cyclopent-1-ene carbaldehyde with, in some cases, high diastereo- and enantioselectivity. Parameters such as water activity, choice of acidic cocatalyst (HX)n and also the amount of cocatalyst used turned out to be crucial for the diastereo- and enantioselectivity of the reaction. 相似文献
20.
Tim den Hartog Derk Jan van Dijken Adriaan J. Minnaard Ben L. Feringa 《Tetrahedron: Asymmetry》2010,21(11-12):1574-1584
A novel iterative approach to the synthesis of the naturally ubiquitous syn deoxypropionate motif is reported. The route comprises a new Horner–Wadsworth–Emmons reagent to prepare α,β,γ,δ-bisunsaturated thioesters. Next, two Me-substituents are introduced in high yield, regio- and enantioselectivity using sequential asymmetric Cu-catalyzed 1,6-conjugate addition, base-catalyzed olefin isomerization and Cu-catalyzed enantioselective 1,4-conjugate addition. After reduction to the aldehyde these transformations can be repeated to install three or more Me groups with a syn 1,3-relationship. 相似文献