共查询到20条相似文献,搜索用时 31 毫秒
1.
Keiko Takahashi Kenjiro Hattori 《Journal of inclusion phenomena and macrocyclic chemistry》1994,17(1):1-24
Cyclodextrins have great potential for exploitation as a useful tool for asymmetric induction. Many kinds of asymmetric reaction have been achieved in the presence of cyclodextrin under various conditions such as the solid phase, heterogeneous suspension or homogeneous aqueous or organic solution. Complexation is essential for asymmetric induction. What is necessary to improve CDs for greater asymmetric induction? 相似文献
2.
《Tetrahedron: Asymmetry》1998,9(21):3797-3817
Palladium-catalyzed asymmetric allylic alkylations were studied by using chiral sulfoxide ligands bearing nitrogen atoms as coordinating elements, such as chiral α-sulfinylacetamides, β or γ-amino sulfoxides, and β-sulfinyl sulfonamides. The effects of the chiral sulfinyl functions on the asymmetric induction were demonstrated. Use of (S)-2-pyrrolidinophenyl p-tolyl sulfoxide or (S)-2-(N-butyl-N-methylaminomethyl)phenyl p-tolyl sulfoxide as chiral ligands in the palladium-catalyzed asymmetric allylic alkylations provided the highest enantioselectivity (50 or 58% e.e., respectively) among chiral sulfoxide ligands examined by us. The participation of the sulfinyl groups in these catalytic asymmetric reactions is rationalized, and the mechanism for the asymmetric induction is proposed on the basis of the stereochemical outcome obtained. 相似文献
3.
Masakatsu Shibasaki Hiroaki Sasai Takayoshi Arai 《Angewandte Chemie (International ed. in English)》1997,36(12):1236-1256
This review focuses on a new concept in catalytic asymmetric reactions that was first realized for the use of heterobimetallic complexes. As these heterobimetallic complexes function as both a Brønsted base and as a Lewis acid, just like an enzyme, they make possible a variety of efficient catalytic asymmetric reactions. This heterobimetallic concept should prove to be applicable to a variety of new asymmetric catalyses. The first part of this review describes the development of rare-earth–alkali metal complexes such as LnM3tris(binaphthoxide) complexes (LnMB, Ln = rare-earth metal, M = alkali metal), which are readily prepared from the corresponding rare-earth trichlorides or rare-earth isopropoxides, and their application to catalytic asymmetric synthesis. By using a catalytic amount of LnMB complexes several asymmetric reactions proceed efficiently to give the corresponding desired products in up to 98% ee: LnLB-catalyzed asymmetric nitroaldol reactions (L = Li), LnSB-catalyzed asymmetric Michael reactions (S ? Na), and LnPB-catalyzed asymmetric hydrophosphonylations of either imines or aldehydes (P ? K). Applications of these heterobimetallic catalysts to the syntheses of several biologically and medicinally important compounds are also described. Spectral analyses and computational simulations of the asymmetric reactions catalyzed by the heterobimetallic complexes reveal that the two different metals play different roles to enhance the reactivity of both reaction partners and to position them. From mechanistic considerations, a useful activation of the heterobimetallic catalyses was realized by addition of alkali metal reagents. The second part describes the development of another type of heterobimetallic catalysts featuring Group 13 elements such as Al and Ga as the central metal. Among them, the AlLibis(binaphthoxide) complex (ALB) is an effective catalyst for asymmetric Michael reactions, tandem Michael–aldol reactions, and hydrophosphonylation of aldehydes. 相似文献
4.
5.
Gröger H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(24):5246-5251
Bifunctional catalysts can drastically improve the efficiency of asymmetric processes with respect to enantioselectivity and/or conversion rate. A new type of chiral bifunctional catalyst has been developed recently in the Shibasaki group that contains both Lewis acid and Lewis base moieties. These monometallic and bifunctional phosphinoyl-containing catalysts are able to coordinate both nucleophilic and electrophilic substrates in the transition state. Several successful applications of this new catalytic concept in the field of asymmetric cyanation reactions have already been reported, for example, the asymmetric hydrocyanation of aldehydes and imines as well as the asymmetric Reissert reaction. The development and principle of this catalytic concept as well as main applications thereof are reviewed in this article. 相似文献
6.
Henrik Sundén 《Tetrahedron letters》2006,47(1):99-103
The organocatalytic asymmetric epoxidation of α,β-unsaturated aldehydes with peroxides or sodium percarbonate is presented. Chiral pyrrolidine derivatives, proline and amino acid derived imidazolidinones mediate the asymmetric epoxidation of α,β-unsaturated aldehydes. For example, commercially available protected α,α-diphenyl-2-prolinol catalyzes the asymmetric formation of 2-epoxy-aldehydes in 81-95% conversion with up to 96:4 dr and 98% ee. The use of non-toxic catalysts, aqueous solvents and hydrogen peroxide or sodium percarbonate as the oxygen sources makes the reaction environmentally benign. 相似文献
7.
The synthetic modification of enantiopure hydroxymethyl-substituted pyridine derivatives leading to novel chiral ligands is described. A set of these pyridine derivatives was examined as ligands in asymmetric transformations such as enantioselective alkylations or alkynylations of aldehydes, the asymmetric copper-catalyzed Henry reaction and the asymmetric allylation of benzaldehyde with allyl(trichloro)silane. This first screening revealed that several of the pyridine derivatives prepared are effective ligands affording high yields and good enantioselectivities. The asymmetric alkylation of aldehydes with diethylzinc provided yields of up to 93% with an enantiomeric excess of up to 88%. The asymmetric Henry reaction was also efficiently catalyzed by one of the prepared ligands affording (S)-2-nitro-1-phenylethanol in 68% yield and with 70% ee. 相似文献
8.
9.
Ibrahem I Zou W Engqvist M Xu Y Córdova A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(23):7024-7029
The direct three-component asymmetric Mannich reaction catalyzed by acyclic chiral amines or amino acids is presented. Simple acyclic chiral amines and amino acids--such as alanine-tetrazole (9), alanine, valine, and serine-catalyzed the three-component asymmetric Mannich reactions between unmodified ketones, p-anisidine, and aldehydes with high chemo- and stereoselectivity, furnishing the corresponding Mannich bases with up to >99 % ee. This study demonstrates that the whole range of amino acids in nature, as well as nonproteogenic amino acid derivatives, can be considered in the design and tuning of novel, inexpensive organocatalysts for the direct asymmetric Mannich reaction. 相似文献
10.
Chiral BINOL-derived Br?nsted acids catalyze the enantioselective asymmetric Morita-Baylis-Hillman (MBH) reaction of cyclohexenone with aldehydes. The asymmetric MBH reaction requires 2-20 mol % of the chiral Br?nsted acid 2e or 2f and triethylphosphine as the nucleophilic promoter. The reaction products are obtained in good yields (39-88%) and high enantioselectivities (67-96% ee). The Br?nsted-acid-catalyzed reaction is the first example of a highly enantioselective asymmetric MBH reaction of cyclohexenone with aldehydes. 相似文献
11.
Pengyi Tang Yongqing Zhao Cailing Xu Kunpeng Ni 《Journal of Solid State Electrochemistry》2013,17(6):1701-1710
An asymmetric supercapacitor based on manganese dioxide/Au/nickel foam (MANF) electrode as positive electrode and graphene or commercial activated carbons (AC) as negative electrode was fabricated. The effect of different negative electrode materials and mass ratios of negative/positive electrodes on the electrochemical properties of the asymmetric supercapacitor was carefully investigated. The results suggest that the mass ratio of negative/positive electrode has a significant impact on the specific capacitance of the asymmetric supercapacitor. Especially, it is found that the optimal mass ratio of the negative/positive electrode is slightly lower than that calculated according to charge balance. On the other hand, the asymmetric supercapacitor with commercialized AC as negative electrode possesses higher specific capacitance and better rate capability than that of the asymmetric supercapacitor with graphene as negative electrode. The negative material has slight impact on the cycle stability of the asymmetric supercapacitor. In addition, the optimized asymmetric supercapacitor with MANF composite as positive electrode and AC as negative electrode can obtain an energy density as high as 65.9 Wh?kg?1 at a power density of 180 W?kg?1 and a cell voltage of 1.8 V in the neutral Na2SO4 aqueous solution. 相似文献
12.
Iridium-based asymmetric reduction of ketones to chiral enantiomerically enriched alcohols has recently attracted attention by a number of research groups and interest in this area is growing. This review presents the different catalytic systems based on iridium complexes that have been used in asymmetric hydrosilylation, in asymmetric transfer hydrogenation (ATH) with alcohols or formic acid derivatives as reducing agents, and in asymmetric hydrogenation (H2 as reducing agent). A large variety of chiral ligands of various denticities and bearing various combination of coordinating atoms (N, P, S, O, C, …) have been used and will be presented. The last part critically reviews the mechanistic understanding of all the above transformations with specific reference to iridium catalysts. 相似文献
13.
Aldol reaction involving chiral amines as organocatalysts through enamine formation, like class-I aldolases, is one of the thriving areas of general interest and widely applicable asymmetric reactions. There are many natural and synthetic chiral templates known to work as efficient organocatalysts, but using carbohydrate templates for chiral induction in asymmetric aldol reactions is a relatively new area developed in the recent years. This review focuses on carbohydrates alone or their conjugates with previously known chiral moieties as organocatalysts for asymmetric aldol reactions. 相似文献
14.
Regioselective asymmetric reduction of prochiral α,β-unsaturated ketones to optically active allylic alcohols was performed via hydrosilylation catalyzed by a rhodium(I) complex with (+)-BMPP, (+)-DIOP and (?)-DIOP as chiral ligands. The allylic alcohols with optical purity up to 69% e.e. were obtained in good yields. The extent of asymmetric induction was found to depend on the stereo-electronic matching of the chiral ligand, ketone and hydrosilane employed. In the asymmetric reduction of (R)-carvone, leading to carveol, the extent of asymmetric induction was found to depend markedly on the ligand/rhodium ratio. Either trans-(5R,1S)-carveol or cis-(5R,1R)-carveol was obtained with good stereoselectivity by using (?)-DIOP or (+)-DIOP as chiral ligand, and it turned out that the chiral center present in carvone had only a slight influence on the asymmetric induction by the chiral catalysts. 相似文献
15.
Yasamin Ghahramani Marzieh Mokhberi Seyyed Mojtaba Mousavi Seyyed Alireza Hashemi Fatemeh Fallahi Nezhad Wei-Hung Chiang Ahmad Gholami Chin Wei Lai 《Molecules (Basel, Switzerland)》2022,27(23)
The undesirable side effects of conventional chemotherapy are one of the major problems associated with cancer treatment. Recently, with the development of novel nanomaterials, tumor-targeted therapies have been invented in order to achieve more specific cancer treatment with reduced unfavorable side effects of chemotherapic agents on human cells. However, the clinical application of nanomedicines has some shortages, such as the reduced ability to cross biological barriers and undesirable side effects in normal cells. In this order, bioinspired materials are developed to minimize the related side effects due to their excellent biocompatibility and higher accumulation therapies. As bioinspired and biomimetic materials are mainly composed of a nanometric functional agent and a biologic component, they can possess both the physicochemical properties of nanomaterials and the advantages of biologic agents, such as prolonged circulation time, enhanced biocompatibility, immune modulation, and specific targeting for cancerous cells. Among the nanomaterials, asymmetric nanomaterials have gained attention as they provide a larger surface area with more active functional sites compared to symmetric nanomaterials. Additionally, the asymmetric nanomaterials are able to function as two or more distinct components due to their asymmetric structure. The mentioned properties result in unique physiochemical properties of asymmetric nanomaterials, which makes them desirable materials for anti-cancer drug delivery systems or cancer bio-imaging systems. In this review, we discuss the use of bioinspired and biomimetic materials in the treatment of cancer, with a special focus on asymmetric nanoparticle anti-cancer agents. 相似文献
16.
Enrique Mann 《Tetrahedron》2008,64(36):8484-8487
Deep cavitands bearing eight asymmetric centers on their upper rims are prepared from octamino resorcinarenes. The resorcinarenes are acylated with Fmoc d- and l-alanine or Fmoc glycine acid chlorides. The asymmetric centers create a chiral magnetic environment as shown by binding achiral ?-caprolactam. The chiral steric environment shows modest enantioselectivity (55% de) for chiral guests such as pinane diols bound inside the cavitand. 相似文献
17.
Chiral C?-symmetric diamines have emerged as versatile auxiliaries or ligands in numerous asymmetric transformations. Chiral 2,2'-bispyrrolidine-based salan ligands were prepared and applied to the asymmetric aryl transfer to aldehydes with arylboronic acids as the source of transferable aryl groups. The corresponding diarylmethanols were obtained in high yields with moderate to good enantioselectivitives of up to 83% ee. 相似文献
18.
Karlheinz Drauz Axel Kleeman Jürgen Martens 《Angewandte Chemie (International ed. in English)》1982,21(8):584-608
Since the stereoisomers of molecules with one or more asymmetric centers often exhibit different biological activities (e.g. thalidomide, pheromones), stereoselective synthesis as a method of preparative chemistry is rapidly attaining importance. Of the numerous drugs prepared by total synthesis that contain at least one asymmetric center, only about 20% have so far been used in sterically pure form. Amino acids constitute the greatest “chiral pool” of compounds whose enantiomers can be obtained commercially in large amounts; they are gradually being used more and more frequently as auxiliary agents or educts in asymmetric syntheses. 相似文献
19.
Asymmetric catalysis under almost‐neutral reaction conditions is key for the efficient synthesis of optically active polar molecules. We have developed catalytic enantioselective reactions of acyclic or cyclic alkenyl esters by using an (S)‐BINOL‐derived chiral tin‐dibromide reagent that possesses a bulky aryl group at the 3 or 3′ position as the chiral pre‐catalyst in the presence of a sodium alkoxide and an alcohol, in which a chiral tin alkoxide bromide is generated in situ and recycled with the assistance of an alcohol. In this Personal Account, we describe three types of asymmetric transformation that proceed through a chiral tin enolate: 1) The asymmetric aldol reaction of alkenyl esters or unsaturated lactones with aldehydes or isatins; 2) the asymmetric three‐component Mannich‐type reaction of alkenyl esters and related cycloaddition reactions; and 3) the asymmetric N‐nitroso aldol reaction of unsaturated lactones with nitrosoarenes. 相似文献
20.
An augmented van der Waals equation of state based on a perturbation theory has been applied to the calculation of high pressure vapour—liquid equilibria for systems containing polar substances. The equation of state comprises four terms, which imply the contributions from repulsion, symmetric, non-polar asymmetric, and polar asymmetric interactions. The characteristic parameters of each pure substance have been determined by three methods with the use of vapour pressures and saturated liquid densities. Mixing models for the terms of the repulsion, symmetric, and non-polar asymmetric interactions are the same as used previously. Two types of mixing models based on a three-fluid model and/or a one-fluid model are developed for the polar asymmetric term. The polar asymmetric term has a large effect on the prediction of the vapour—liquid equilibrium. With the introduction of a binary interaction parameter, the equation is found to be useful in correlating the vapour—liquid equilibria for a system containing a polar substance except near a critical region. 相似文献