共查询到20条相似文献,搜索用时 15 毫秒
1.
Since the pioneering finding by List and Barbas III and their coworkers that L-proline could work as a catalyst in the intermolecular direct aldol reaction, the concept of small organic molecules as catalysts has received great attention. However, new organic molecule which have better catalysis ability are reported scarcely. Our groups1 found L-Prolinamides 1 to be active catalysts for the direct aldol reaction of 4-nitrobenaldehyde with neat acetone at room temperature. The enantioselecti… 相似文献
2.
[reaction: see text] L-Proline-based small peptides have been developed as efficient catalysts for the asymmetric direct aldol reactions of hydroxyacetone with aldehydes. Chiral 1,4-diols 7, which are disfavored products in similar aldol reactions catalyzed by either aldolases or L-proline, were obtained in high yields and enantioselectivities of up to 96% ee with peptides 3 and 4 in aqueous media. 相似文献
3.
4.
A homochiral metal-organic triangle Co-Pro1 was achieved via self-assembly by incorporating a L-proline moiety within the corresponding ligand. Co-Pro1 comprised L-proline moieties as asymmetric catalytic active sites and a helical-like cavity, it worked as an asymmetric catalyst to prompt aldol reactions with size-, stereo- and enantioselectivity. 相似文献
5.
[reaction: see text] L-proline failed to act as an organocatalyst in the homoaldol reaction of ethyl pyruvate; however, it reacted with the ester to give an azomethine ylide that in turn underwent 1,3-dipolar cycloaddition with a second molecule of pyruvate. Direct catalytic homoaldol reaction of ethyl pyruvate was performed using an (S)-(+)-1-(2-pyrrodinylmethyl)pyrrolidine/trifluoroacetic acid combination as organocatalyst. The use of polymer-supported reagents allowed for the lactonization of the aldol and isolation of the isotetronic acid derivative in hydroxy-free form. 相似文献
6.
WANG Rui WEI Zhonglin GUO Jing FENG Yusha XU Enjie DUAN Haifeng LIN Yingjie YANG Qingbiao DU Jianshi LI Yaoxian 《高等学校化学研究》2018,34(2):180-185
Chiral organocatalysts of 4-adamantane amide based on L-proline with double hydrogen potential were synthesized and used in asymmetric aldol reactions. The reactions were evaluated in toluene under -20℃. A series of aldol products was obtained from moderate to good yields(up to 98%) with excellent diastereoselectivities(up to >99:1) and enantioselectivities(up to >99%). The aldol products in the system were separated by α-cyclodextrin via host-guest interaction and determined by chiral HPLC. The catalyst could be reused up to five times. The 4-substitution position played an important role in diastereoselectivity and enantioselectivity. 相似文献
7.
Chen XH Luo SW Tang Z Cun LF Mi AQ Jiang YZ Gong LZ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(2):689-701
An organocatalyst prepared from (2R,3R)-diethyl 2-amino-3-hydroxysuccinate and L-proline exhibited high regio- and enantioselectivities for the direct aldol reactions of hydroxyacetone and fluoroacetone with aldehydes in aqueous media. It was found that water could be used to control the regioselectivity. The presence of 20-30 mol% of the catalyst afforded the direct aldol reactions of a wide range of aldehydes with hydroxyacetone to give the otherwise disfavored products with excellent enantioselectivities, ranging from 91 to 99% ee, and high regioselectivities. Aldolizations of fluoroacetone with aldehydes mediated by 30 mol% of the organocatalyst in aqueous media preferentially occurred at the methyl group, yielding products with high enantioselectivities (up to 91% ee); however, these additions took place dominantly at the fluoromethyl group in THF. Optically active 3,5-disubstituted tetrahydrofurans and (2S,4R)-dihydroxy-4-biphenylbutyric acid were prepared by starting from the aldol reaction of hydroxyacetone. Theoretical studies on the role of water in controlling the regioselectivity revealed that the hydrogen bonds formed between the amide oxygen of proline amide, the hydroxy of hydroxyacetone, and water are responsible for the regioselectivity by microsolvation with explicit one water molecule as a hydrogen-bond donor and/or an acceptor. 相似文献
8.
A diastereo- and enantioselective aldol reaction between aldehydes and a synthetically useful ketomalonate 1c as a hydrated form was developed, and either anti- or syn-aldol adducts having a chiral tetrasubstituted carbon center were obtained in high enantioselectivities by use of a tetrazole analogue of L-proline (S)-2 or an axially chiral amino sulfonamide (S)-3 as catalyst. 相似文献
9.
Chandrasekhar S Narsihmulu Ch Reddy NR Sultana SS 《Chemical communications (Cambridge, England)》2004,(21):2450-2451
We demonstrate for the first time, L-proline as a chiral catalyst for transfer aldol reaction between aldehydes and diacetone alcohol. 相似文献
10.
[reaction: see text] Using L-proline as catalyst in the asymmetric aldol reaction and a series of benzamides and naphthamides, we have accomplished a dynamic kinetic resolution that simultaneously establishes the stereochemistry of the atropisomeric amide's chiral axis and a stereogenic center. The enantioselectivities ranged from 82% to 95% and the diastereoselectivities from 2.1:1 to 7.0:1. 相似文献
11.
A simple and efficient composite catalyst of L-proline–polyethyleneglycol(PEG)–SiO2 was developed for the asymmetric aldol reaction between acetone and p-nitrobenzaldehyde. With 10 mol% L-proline, the composite catalyst showed much better yield and enantioselectivity than the pristine L-proline over 1.5 h. Clear effects of the molecular weight of PEG and the properties of silica supports on the yield and enantioselectivity were observed, and the optimized catalyst can be reused for four cycles with stable performance. 相似文献
12.
13.
MBHA resin-supported tripeptide catalyst system containing L-proline unit has been developed for use in the direct asymmetric aldol reaction of acetone and aldehydes,which afford the corresponding products with satisfactory isolated yields and enantiomeric excesses. 相似文献
14.
15.
The aldol reaction catalyzed by L-proline has been monitored and the accepted mechanism confirmed by intercepting and characterizing, for the first time, all the proposed intermediates by ESI-MS/MS. 相似文献
16.
We have prepared a range of well-defined copolymers of styrene and L-proline functionalized styrene (5-11 kDa) using reversible addition-fragmentation chain transfer (RAFT) polymerization techniques and explored their use in supported catalysis. Upon deprotection of the L-proline functionalities, the solution self-assembly of these copolymers was investigated in mixed solvent systems. The resulting assemblies were characterized by dynamic light scattering, transmission electron microscopy (on graphene oxide substrates, along with cryo-TEM and tomography), and scanning electron microscopy. The application of these functional assemblies as supported catalysts for the aldol condensation reaction was explored using cyclohexanone and 4-nitrobenzaldehyde. The rate and selectivity of solution catalysis in our self-assembled system were comparable to those of L-proline, and a significant advantage of our system was that the polymer support could be utilized at lower catalyst loadings with comparable activity and also could be recycled a number of times while maintaining activity and selectivity. 相似文献
17.
A proline functionalized fiber catalyst was employed for aldol reactions in water. In the presence of the fiber catalyst, the aldol reactions proceeded smoothly at 40℃ and the products were obtained in excellent yields which were higher than those obtained for the reactions catalyzed by L-proline or trans-4-hydroxy-L-proline. This newly developed fiber catalyst is applicable to the reactions of a wide range of aromatic aldehydes and exhibits excellent reusability(up to 6 times) without any additional treatment. 相似文献
18.
在复杂的天然产物合成和生物合成中,醇醛缩合反应是一类重要的碳-碳键形成反应.不对称催化直接Aldol反应由于其原子经济性,操作简捷,符合绿色化学的要求等,成为近年来不对称合成研究的热点之一. 相似文献
19.
Li HJ Tian HY Chen YJ Wang D Li CJ 《Chemical communications (Cambridge, England)》2002,(24):2994-2995
Asymmetric Mukaiyama aldol reactions in aqueous media (water-ethanol = 9:1) were catalyzed by chiral gallium catalysts with semi-crown ligands to give aldol products with good yields, syn-diastereoselectivities and enantioselectivities. 相似文献
20.
Direct asymmetric intermolecular aldol reactions catalyzed by amino acids and small peptides 总被引:1,自引:0,他引:1
Córdova A Zou W Dziedzic P Ibrahem I Reyes E Xu Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(20):5383-5397
In nature there are at least nineteen different acyclic amino acids that act as the building blocks of polypeptides and proteins with different functions. Here we report that alpha-amino acids, beta-amino acids, and chiral amines containing primary amine functions catalyze direct asymmetric intermolecular aldol reactions with high enantioselectivities. Moreover, the amino acids can be combined into highly modular natural and unusual small peptides that also catalyze direct asymmetric intermolecular aldol reactions with high stereoselectivities, to furnish the corresponding aldol products with up to >99 % ee. Simple amino acids and small peptides can thus catalyze asymmetric aldol reactions with stereoselectivities matching those of natural enzymes that have evolved over billions of years. A small amount of water accelerates the asymmetric aldol reactions catalyzed by amino acids and small peptides, and also increases their stereoselectivities. Notably, small peptides and amino acid tetrazoles were able to catalyze direct asymmetric aldol reactions with high enantioselectivities in water, while the parent amino acids, in stark contrast, furnished nearly racemic products. These results suggest that the prebiotic oligomerization of amino acids to peptides may plausibly have been a link in the evolution of the homochirality of sugars. The mechanism and stereochemistry of the reactions are also discussed. 相似文献