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1.
Arghya Sadhukhan Dr. Noor‐ul H. Khan Tamal Roy Dr. Rukhsana I. Kureshy Dr. Sayed H. R. Abdi Dr. Hari C. Bajaj 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5256-5260
A chiral cobalt(III) complex ( 1 e ) was synthesized by the interaction of cobalt(II) acetate and ferrocenium hexafluorophosphate with a chiral dinuclear macrocyclic salen ligand that was derived from 1R,2R‐(?)‐1,2‐diaminocyclohexane with trigol bis‐aldehyde. A variety of epoxides and glycidyl ethers were suitable substrates for the reaction with water in the presence of chiral macrocyclic salen complex 1 e at room temperature to afford chiral epoxides and diols by hydrolytic kinetic resolution (HKR). Excellent yields (47 % with respect to the epoxides, 53 % with respect to the diols) and high enantioselectivity (ee>99 % for the epoxides, up to 96 % for the diols) were achieved in 2.5–16 h. The CoIII macrocyclic salen complex ( 1 e ) maintained its performance on a multigram scale and was expediently recycled a number of times. We further extended our study of chiral epoxides that were synthesized by using HKR to the synthesis of chiral drug molecules (R)‐mexiletine and (S)‐propranolol. 相似文献
2.
Chengjun Jiang 《Kinetics and Catalysis》2011,52(5):691-696
The highly enantioselective hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by bimetallic chiral (salen)Co
and (salen)Co(III)-OAc mixture provides a simple and effective method for the synthesis of enantiomerically enriched terminal
epoxides (ee > 99%) and diols. At the equimolar amounts of bimetallic chiral (salen)Co and (salen)Co(II)-OAc, the catalytic activity increases
more than two times in comparison with (salen)Co(III)-OAc used alone. The mixed catalytic system can be recycled and reused.
No significant loss of catalytic activity was observed after three runs. 相似文献
3.
Schaus SE Brandes BD Larrow JF Tokunaga M Hansen KB Gould AE Furrow ME Jacobsen EN 《Journal of the American Chemical Society》2002,124(7):1307-1315
The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)Co(III) complex 1 x OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H(2)O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to > or = 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H(2)O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (k(rel)) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, k(rel) values for the HKR exceed 50, and in several cases are well in excess of 200. 相似文献
4.
The asymmetric hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by new easily synthesized dimeric chiral (salen)Co bearing Al, provides a practical and straightforward method for the synthesis of enantiomerically enriched terminal epoxides (>99% ee) and diols. An inorganic acid, HCl is applied first time for the asymmetric ring opening reaction of terminal epoxides. Reactions are conveniently carried out at room temperature under an air atmosphere. 相似文献
5.
Oh CR Choo DJ Shim WH Lee DH Roh EJ Lee SG Song CE 《Chemical communications (Cambridge, England)》2003,(9):1100-1101
In the chiral Co(III)(salen)-catalysed HKR of racemic epoxides, in the presence of ionic liquids, Co(II)(salen) complex is oxidised without acetic acid to catalytically active Co(III)(salen) complex during reaction and, moreover, this oxidation state is stabilised against reduction to Co(II) complex which enables the reuse of the recovered catalyst for consecutive reactions without extra reoxidation. 相似文献
6.
Although application of light-fluorous techniques facilitates the isolation of reaction products from the hydrolytic kinetic resolution (HKR) of terminal epoxides catalysed by cobalt complexes of salen ligands, the extension of the original fluorous biphasic approach to this reaction is far from being a trivial exercise. The nature of the counter anion has a dramatic effect on the catalytic activity of heavily fluorinated chiral (salen) cobalt(III) complexes. Excellent enantioselectivities are obtained in the fluorous biphasic HKR of 1,2-hexene oxide when fluorinated anions are introduced (e.e.s up to 99% both for the diol and the epoxide), with C8F17COO- affording reaction rates even higher than those observed with non-fluorous systems. 相似文献
7.
Rahul B. Kawthekar 《合成通讯》2013,43(8):1236-1248
Novel bimetallic chiral Co (salen) complexes bearing transition‐metal salts have been synthesized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity in hydrolytic kinetic resolution (HKR) of racemic terminal epoxides and consequently provided enantiomerically enriched epoxides (up to 99% ee). 相似文献
8.
Gill CS Venkatasubbaiah K Phan NT Weck M Jones CW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(24):7306-7313
The Co(III)--salen-catalyzed (salen=N,N'-bis(salicylidene)ethylenediamine dianion) hydrolytic kinetic resolution (HKR) of racemic epoxides has emerged as a highly attractive and efficient method of synthesizing chiral C(3) building blocks for intermediates in larger, more complex molecules. HKR reaction rates have displayed a second order dependency on the concentration of active sites, and thus researchers have proposed a bimetallic transition state for the HKR mechanism. Here we report the utilization of pendant Co(III)--salen catalysts on silica supported polymer brushes as a catalyst for the HKR of epichlorohydrin. The novel polymer brush architecture provided a unique framework for promoting site-site interactions as required in the proposed bimetallic transition state of the HKR mechanism. Furthermore, the polymer brushes mimic the environment of soluble polymer-based catalysts, whereas the silica support permitted facile recovery and reuse of the catalyst. The polymer brush catalyst displayed increased activities over the soluble Jacobsen Co--salen catalyst and was observed to retain its high enantioselectivities (>99 %) after each of five reactions despite decreasing activities. Analysis indicated decomposition of the salen ligand as an underlying cause of catalyst deactivation. 相似文献
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11.
Nielsen LP Stevenson CP Blackmond DG Jacobsen EN 《Journal of the American Chemical Society》2004,126(5):1360-1362
The mechanism of the hydrolytic kinetic resolution (HKR) of terminal epoxides was investigated by kinetic analysis using reaction calorimetry. The chiral (salen)Co-X complex (X = OAc, OTs, Cl) undergoes irreversible conversion to (salen)Co-OH during the course of the HKR and thus serves as both precatalyst and cocatalyst in a cooperative bimetallic catalytic mechanism. This insight led to the identification of more active catalysts for the HKR of synthetically useful terminal epoxides. 相似文献
12.
Park J Lang K Abboud KA Hong S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(7):2236-2245
A series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-urea hydrogen-bonding interactions. These bis-urea (salen)Co catalysts resulted in rate acceleration (up to 13 times) in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in THF by facilitating cooperative activation, compared to the monomeric catalyst. In addition, one of the bis-urea (salen)Co(III) catalyst efficiently resolves various terminal epoxides even under solvent-free conditions by requiring much shorter reaction time at low catalyst loading (0.03-0.05 mol %). A series of kinetic/mechanistic studies demonstrated that the self-association of two (salen)Co units through urea-urea hydrogen bonds was responsible for the observed rate acceleration. The self-assembly study with the bis-urea (salen)Co by FTIR spectroscopy and with the corresponding (salen)Ni complex by (1)H NMR spectroscopy showed that intermolecular hydrogen-bonding interactions exist between the bis-urea scaffolds in THF. This result demonstrates that self-assembly approach by using non-covalent interactions can be an alternative and useful strategy toward the efficient HKR catalysis. 相似文献
13.
Zheng Hong ZHOU Zhao Ming LI Bing LIU Kang Ying LI Li Xin WANG Guo Feng ZHAO Qi Lin ZHOU Chu Chi TANG State Key Laboratory of Elemento-Organic Chemistry Institute of Elemento-Organic Chemistry Nankai University Tianjin 《中国化学快报》2006,(2)
As an important strategy for the formation of 1,2-bifunctionalized systems theasymmetric ring-opening of epoxides with different nucleophiles has drawn muchattention from the organic chemists. A wide variety of nucleophiles are utilized in theaforemention… 相似文献
14.
The (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides is a bimetallic process with a rate controlled by partitioning between a nucleophilic (salen)Co-OH catalyst and a Lewis acidic (salen)Co-X catalyst. The commonly used (salen)Co-OAc and (salen)Co-Cl precatalysts undergo complete and irreversible counterion addition to epoxide during the course of the epoxide hydrolysis reaction, resulting in quantitative formation of weakly Lewis acidic (salen)Co-OH and severely diminished reaction rates in the late stages of HKR reactions. In contrast, (salen)Co-OTs maintains high reactivity over the entire course of HKR reactions. We describe here an investigation of catalyst partitioning with different (salen)Co-X precatalysts and demonstrate that counterion addition to epoxide is reversible in the case of the (salen)Co-OTs. This reversible counterion addition results in stable partitioning between nucleophilic and Lewis acidic catalyst species, allowing highly efficient catalysis throughout the course of the HKR reaction. 相似文献
15.
Zhenghong Zhou Zhaoming Li Qilin Zhou Chuchi Tang 《Journal of organometallic chemistry》2006,691(26):5790-5797
A series of chiral bis-Schiff bases were synthesized starting from (1R,2R)-(+)-diaminocyclohexane, (+)-cis-1,2,2-trimethyl-1,3-diaminocyclopentane, (R)-2,2′-diamino-1,1′-binaphthalene, and (1S,2S)-diphenyl-1,2-ethanediamine. The enantioselective ring-opening of meso epoxides with dithiophosphorus acids catalyzed by a (salen)Ti(IV) complex formed in situ upon the treatment of Ti(OPr-i)4 and the aforementioned chiral Schiff base was realized. The resulting products were obtained with low to good enantioselectivities (up to 73% ee). The (salen)Ti(IV) complex containing the backbone of 1,2-diaminocyclohexane exhibited the best enantioselectivity. The substituents in dithiophosphorus acids and those on the salen aromatic ring have a significant influence on the reaction. Moderate enantioselectivity were obtained for the (salen)Ti(IV) complex catalyzed ring-opening of racemic monosubstituted epoxides. High regioselectivity was observed for the alkyl substituted epoxides, whereas poor regioselectivity was obtained for the aryl substituted ones. 相似文献
16.
Chiral nanoporous metal-organic frameworks are constructed by using dicarboxyl-functionalized chiral Ni(salen) and Co(salen) ligands. The Co(salen)-based framework is shown to be an efficient and recyclable heterogeneous catalyst for hydrolytic kinetic resolution (HKR) of racemic epoxides with up to 99.5% ee. The MOF structure brings Co(salen) units into a highly dense arrangement and close proximity that enhances bimetallic cooperative interactions, leading to improved catalytic activity and enantioselectivity in HKR compared with its homogeneous analogues, especially at low catalyst/substrate ratios. 相似文献
17.
《Tetrahedron: Asymmetry》2003,14(22):3589-3592
The hydrolytic kinetic resolution of racemic terminal epoxides utilizing chiral (salen)Co(III) catalysts provides practical access to enantiopure epoxides and diols. However, general issues surrounding catalyst activation combined with the specific problem of racemization of epichlorohydrin served to make the large-scale production of (R)- or (S)-epichlorohydrin difficult and uneconomical. A process for the large-scale production and isolation of active (salen)Co(III)OAc catalyst and a method of catalyst reduction after reaction using ascorbic acid have been developed to overcome these issues. 相似文献
18.
研究了3-(1-萘氧基)-1,2-环氧丙烷[(R,S)-1]在Salen Co(Ⅲ)催化下的水解动力学拆分(HKR)。以转化率和ee值为指标,考察了催化剂用量、底物用量、反应温度、反应时间、溶剂种类等对HKR反应的影响。最佳HKR条件为:(R,S)-1 10 mmol,w[Salen Co(Ⅲ)]=0.75%,THF 1 mL,水0.5 eq,于25℃水解40 h,(R,S)-1的转化率为49.5%,(S)-1的ee为99.5%。 相似文献
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Crosslinked polymeric salen-Co(III) complexes derived from a novel dialdehyde and a trialdehyde were synthesized and employed in the hydrolytic kinetic resolution (HKR) of terminal epoxides. Up to 99% ee were obtained with only 0.16-0.02 mol% of catalyst (based on catalytic unit). 相似文献