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1.
Asymmetric catalysis has always been the focus of attention for synthetic chemistry. In this review, we summarize recent advances in the synthesis and asymmetric catalysis application of chiral metal clusters, nanoclusters and nanoparticles. 相似文献
2.
Zackary Crane 《Tetrahedron》2005,61(26):6409-6417
Several ketone catalysts containing spiro ethers and lactones have been investigated for the asymmetric epoxidation of olefins. The results showed that substituents on the spiro ring of the ketone catalysts have profound effects on enantioselectivity. Results also suggested that the high enantioselectivities previously observed for conjugated cis-olefins with oxazolidinone containing ketones could be partially due to attractive interactions between the Rπ group of the olefin and the carbonyl group of the oxazolidinone. In addition, nonbonding interactions such as van der Waals forces and/or hydrophobic interactions between the olefin substituents and the nitrogen substituents of the oxazolidinone may also be involved in stereodifferentiation. The information gained provides additional understanding of factors important for ketone catalyzed epoxidations. 相似文献
3.
Enantioselective direct α-hydroxyamination and α-aminoxylation of α-branched aldehydes using a proline-derived tetrazole catalyst is described herein. α-Hydroxyamination adducts with up to 90% ee were obtained by the reaction of nitrosobenzene with unactivated α-branched aldehydes under mild reaction conditions. 相似文献
4.
Chiral 2-pyridylsulfinamides were shown to be effective catalysts in the alkylation of aryl and alkyl aldehydes with diethylzinc providing the corresponding alcohols in excellent enantioselectivity. Sulfinamide catalysts possessing solitary chirality at the sulfur center produced the product phenethyl alcohol in good enantioselectivity. Diastereomeric sulfinamides possessing chirality at the carbon-bearing nitrogen and at the sulfur of the sulfinamide increased the enantioselectivity of the product alcohols up to >99%. However, there is no effect of the match-mismatch pair of sulfinamide diastereomers on the outcome of the chiral induction of the product phenethyl alcohols. It was conclusively proved that chirality at the sulfur center is mandatory for obtaining good enantioselectivity in the reaction. 相似文献
5.
A catalytic asymmetric brominative dearomatization reaction of benzofuran derivatives was achieved by using hydroquinidine 1,4-phthalazinediyl diether [(DHQ)2PHAL] as the catalyst and N-bromoacetamide (NBAc) as the brominating reagent. A series of brominated spiro[benzofuran-2,5'-oxazoles] bearing two contiguous stereogenic centers were obtained in high yields (up to 99%) with excellent enantioselectivity (up to 97% ee). 相似文献
6.
Ricardo S. Schwab Juliano B. Azeredo Diogo S. Lüdtke Márcio W. Paixão 《Tetrahedron letters》2008,49(34):5094-5097
In this Letter, a cysteine-derived prolinamide is described to act as a robust and effective organocatalyst for enantioselective aldol reactions. 相似文献
7.
Direct catalytic asymmetric vinylogous reaction serves as a powerful tool to introduce stereocenter(s) at the γ- or/and even more remote position(s) of the vinylogous products in an atom-economical and efficient way. A variety of direct catalytic asymmetric vinylogous reactions with broad substrate scope and mild reaction conditions has been developed. Both metal catalysis and organocatalysis contributed in this field and led to the vinylogous products in high stereoselectivity. These vinylogous reactions provided efficient pathways for the synthesis of highly functionalized optically pure compounds, especially these with potential biological activity and pharmacological activity. This digest paper mainly focuses on the most recent developments in this field, including both nucleophilic addition and nucleophilic substitution. 相似文献
8.
Ahmed M Bronger RP Jackstell R Kamer PC van Leeuwen PW Beller M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(35):8979-8988
The application of phenoxaphosphino-modified Xantphos-type ligands (1-9) in the rhodium-catalyzed hydroaminomethylation of internal olefins to give linear amines is reported. Excellent chemo- and regioselectivities have been obtained through the use of 0.1 mol % [Rh(cod)2]BF(4)/0.4 mol % xantphenoxaphos (1), providing a practical and environmentally attractive synthetic route for the preparation of amines from internal alkenes. For the first time, both functionalized internal olefins and mixtures of internal and terminal olefins have been converted highly selectively into linear amines. Investigations of the effects of the calculated natural bite angles of ligands on hydroaminomethylation shows that the regioselectivity for the linear product follows a similar trend to that seen in the hydroformylation of internal alkenes with the aid of these ligands. Hydroaminomethylation and each of its individual steps were monitored by high-pressure infrared spectroscopy. The results suggest that hydroaminomethylations take place by a sequential isomerization/hydroformylation/amination/hydrogenation pathway. 相似文献
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11.
Several oxindole derivatives, of natural or synthetic origin, have been identified as medicinally appealing compounds, with a plethora of bioactivities reported. Chiral 3-hydroxy and 3-aminooxindole scaffolds have captured the attention of several research groups, due to their importance in drug discovery. In this review, we systematically address the wide variety of asymmetric catalytic methodologies employed in the preparation of these relevant chiral scaffolds, present in many biologically active compounds and/or natural products. Special focus will be given to the nature of the catalyst used. 相似文献
12.
Phosphine-catalyzed enantioselective γ-additions of rhodanines to allenoates have been developed for the first time. With the employment of chiral cyclohexane-based phosphines, a wide range of substituted rhodanine derivatives containing tertiary chiral centers were constructed in good yields and high enantioselectivities. 相似文献
13.
Pharmacologically active 4,4-diarylbutylamines like Fluspirilene and 4-amino-1,1-diarylbutan-1-ols like Difenidol were prepared in high yields via rhodium catalysed hydroaminomethylation of 1,1-diaryl-allylalcohols. Conversion of these olefins with carbon monoxide, hydrogen and secondary amines proceeds with complete regioselectivity. This group can easily be removed under acidic and hydrogenating conditions, enabling the transformation of 4-amino-1,1-diarylbutan-1-ols to 4,4-diarylbutylamines in high yields. Thus Fluspirilene was synthesised in 88% yield in four steps starting from commercially available materials. 相似文献
14.
Beno?ˆt Gadenne 《Tetrahedron letters》2004,45(44):8157-8160
New hydrophobic ionic liquids containing chiral camphorsulfonamide units were used as chiral auxiliaries in the titanium catalyzed asymmetric diethylzinc addition to benzaldehyde. The ionic catalyst system shows catalytic properties similar to those of related nonionic counterparts in terms of activity and enantioselectivity. Interestingly, the ionic ligands can easily be recycled and re-used without loss of activity or selectivity. 相似文献
15.
An efficient organocatalytic diastereo- and enantioselective method for the construction of spirocyclic oxindole derivatives bearing two spiro quaternary centers and three consecutive stereocenters via a domino Michael/cyclization process has been developed. Using commercially available quinine as catalyst, the reactions of 3-isothiocyanato oxindoles with unsaturated pyrazolones and unsaturated isoxazolones proceeded smoothly under mild reaction conditions for giving two classes of spirocyclic oxindole compounds in high to excellent yields with moderate to good diastereoselectivities and enantioselectivities. A plausible dual activation working model was tentatively proposed to account for the stereochemistry of the domino Michael/cyclization process. 相似文献
16.
Julia HermekePatrick H. Toy 《Tetrahedron》2011,67(22):4103-4109
The attachment of phosphonium ion phase tags to chiral binapthyl-based phosphoric acid catalysts, and the use of these materials in a range of organocatalytic asymmetric Friedel-Crafts reactions of indoles has been studied. Placement of the tags at the 3 and 3′ positions of the phosphoric acid, so that they could serve as steric blocking groups, failed to produce an active catalyst. However, moving the phosphonium ion groups to the 6 and 6′ positions produced an efficient and enantioselective catalyst. Aided by the presence of the phase tags, the chiral catalyst was easily removed at the end of the reactions, and could be reused several times, albeit with somewhat decreased efficiency and enantioselectivity. 相似文献
17.
A rationally designed organocatalyst for direct asymmetric aldol reaction in the presence of water has been developed. High yield (up to 99%), diastereoselectivity (up to 99:1) and enantioselectivity (up to 97%) were obtained under optimal conditions. 相似文献
18.
Santosh Singh Thakur Wenji Li Seong-Jin Kim Geon-Joong Kim 《Journal of organometallic chemistry》2006,691(9):1862-1872
A new dinuclear chiral Co(salen) complexes bearing group 13 metals have been synthesized and characterized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of epoxides with H2O, chloride ions and carboxylic acids and consequently provide enantiomerically enriched terminal epoxides (>99% ee). It also catalyzes the asymmetric cyclization of ring opened product, to prepare optically pure terminal epoxides in one step. The homogeneous dinuclear chiral Co(salen) have been covalently immobilized on MCM-41. The potential benefits of heterogenization include facilitation of catalyst separation and recyclability requiring very simple techniques. The system described is very efficient. 相似文献
19.
The current applications of ruthenium porphyrins in stoichiometric and catalytic asymmetric reactions are reported. Chiral recognition of racemic phosphines, isocyanides and amino esters has been studied by 1H-NMR. Experimental investigations of the oxidation mechanism of racemic phosphines and amino esters are described. The stereochemistry of catalytic asymmetric oxidation and cyclopropanation of olefins with optically active ruthenium porphyrins are also discussed. 相似文献
20.
Adam J. Davenport John Fawcett David R. Russell 《Journal of organometallic chemistry》2006,691(10):2221-2227
Reaction of [RhCl2Cp*]2 (Cp* = η-C5Me5) with salicyloxazolines in the presence of NaOMe gives complexes [RhCl(R-saloxaz)Cp*] (1-4) which have been fully characterised. The diastereoselectivity of complexation depends on the substituents and the absolute configuration at the metal centre is unstable in solution. Treatment of 2 with 4-methylpyridine and NaSbF6 in methanol at reflux gave [Rh(4-Mepy){(S)-iPr-saloxaz}Cp*][SbF6] (5) whilst [Rh(OH2)(Me2-saloxaz)Cp*][SbF6] (6) was prepared by reaction of 1 with AgSbF6. Three complexes, [RhCl(Me2-saloxaz)Cp*] (1), [RhCl{(S)-iPr-saloxaz}Cp*] (2), and [Rh(OH2)(Me2-saloxaz)Cp*][SbF6] (6) have been characterised by X-ray crystallography. Some of the complexes, after treatment with AgSbF6, have been tested as enantioselective catalysts for the Diels-Alder reaction of methacrolein with cyclopentadiene. 相似文献