共查询到20条相似文献,搜索用时 15 毫秒
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Marian Mikoßajczyk Piotr ßyżwa Józef Drabowicz 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):357-358
Addition of α-phosphonate carbanions to (S)-sulfinimines 2 gives N-sulfinyl-β-aminophosphonates 3 with a high diastereoselectivity (up to 10:1). The major diastereomer of 3 (R=Ph) was converted into (+)-(R)-β-amino-β-phenylethanephosphonic acid 5. 相似文献
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Some chiral oxazaborolidinones were prepared from L-α-amino acids reacting with borane and used as a new type of catalysts for asymmetric reduction of acetophenone with borane to afford R-(+)-1-phenyl ethanol with 23–76%ee in high yield. 相似文献
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Loïc Roupnel Régis Guillot Didier Gori Baby Viswambharan Cyrille Kouklovsky Valérie Alezra 《Helvetica chimica acta》2021,104(10):e2100127
We describe here an asymmetric aldol reaction based on the principle of Memory of Chirality. From α-amino acids such as leucine and methionine, we have synthesized in two steps quaternary α-amino acid derivatives with high diastereoselectivity and enantioselectivity, using the chirality of the initial α-amino acid as the only chirality source. Furthermore, we were able to determine the relative and absolute configurations of the aldol products thanks to crystallographic structures and thus showed that the relative configuration depended on the aldehyde employed. We proposed a stereoselectivity explanation and obtained also quaternary β-hydroxy α-amino acids after acidic hydrolysis. 相似文献
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ZHANG Zhi-Hui LI Shuo XU Pen-gFei 《有机化学》2003,23(Z1):418-418
β-hydroxy-α-amino acids constitute an important class of compounds as naturally occurring amino acids and as components of many complex natural products possessing a wide range of biological activities. [1] As a consequence of the essential role played by these amino acids in the biological systems and their utility as synthetic building blocks, a number of useful strategies have been devised for their preparation. [2] 相似文献
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A series of β-amino alcohols derived from (1R, 2S)-2-amino-1,2-diphenylethanol and substituted salicylaldehydes as novel chiral tridentate ligands has been applied to an asymmetric Reformatsky reaction of aldehydes with ethyl iodoacetate in the presence of ZnMe2. This novel catalytic system produced the desired β-hydroxyl esters with moderate to good enantioselectivities (up to 81% ee) and yields for many aldehydes, including aromatic, heteroaromatic, conjugated, and aliphatic aldehydes. 相似文献
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Abstract The direct asymmetric aldol reaction catalyzed by the simple and commercially available chiral primary diamines, (1S,2S)-1,2-diphenylethane-1,2-diamine and (1R,2R)-1,2-diphenylethane-1,2-diamine, is presented. The catalyst system is a primary amine with Br?nsted acid–catalyzed direct aldol reaction of p-nitrobenzaldehyde and cyclohexanone with high chemo- and stereoselectivity on water, which furnishes the corresponding β-hydroxyketone with up to 94% ee. 相似文献
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Nadezhda V. Stoletova Andrey D. Moshchenkov Alexander F. Smol'yakov Zalina T. Gugkaeva Victor I. Maleev Dmitry Katayev Vladimir A. Larionov 《Helvetica chimica acta》2021,104(1):e2000193
Perfluoroalkylated α-amino acids (PFAAs) are a unique class of compounds for biochemistry and pharmaceutical science. In this context, we report the successful intermolecular coupling of the Belokon’s chiral dehydroalanine Ni(II) complex with a variety of perfluoroalkyl iodides. A 4-cyanopyridine/B2Pin2 catalytic system generates perfluoroalkyl radicals, which after trapping by the ligand sphere of a chiral Ni(II) complex provide the diastereomeric complexes with up to >20 : 1 dr (seven examples). The obtained major (S,S)-diastereomers were easily isolated by simple silica column chromatography in 33–54 % yields. The perfluoroalkylated α-AA was subsequently released from the obtained Ni(II) complex through aqueous HCl treatment. The chiral auxiliary ligand ((S)-BPB=(S)-2-(N-benzylprolyl)aminobenzophenone) can be easily recycled after the acidic complex decomposition and reused for the synthesis of the starting dehydroalanine Ni(II) complex. 相似文献
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Cangsong Liao Florian P. Seebeck 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(18):7251-7254
This report describes a modular enzyme-catalyzed cascade reaction that transforms l - or d -α-amino acids to β-methyl-α-amino acids. In this process an α-amino acid transaminase, an α-keto acid methyltransferase, and a halide methyltransferase cooperate in two orthogonal reaction cycles that mediate product formation and regeneration of the cofactor pyridoxal-5′-phosphate and the co-substrate S-adenosylmethionine. The only stoichiometric reagents consumed in this process are the unprotected l - or d -α-amino acid and methyl iodide. 相似文献
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The application of Wolff rearrangement of the diazoketones derived from α-amino acids has been well documented.1 It has been generally observed that if the rearrangement is performed in aqueous solution, homologated acid is the expected products, while if the reaction is run in methanol or ammonia, the corresponding homologated ester or amide will be obtained. In connection with other synthetic work, we unexpectedly observed that the Wolff rearrangement of diazoketone 1 in anhydrous methanol gave exclusively γ-lactam 3 in excellent yield.(Scheme 1) The formation of this intramolecular cyclization product was apparently due to the nucleophilic attack of the intermediate ketene 2 by the tosyl protected amino group. Although the solvent methanol can serve as nucleophile, the exclusive formation of γ-lactam indicates the intermolecular nucleophilic attack of the ketene intermediate 2 by methanol is not effective enough to compete with intramolecular nucleophilic attack by the tosyl protected amino group. This observation aroused our interest in the generality of this reaction and its potential as a novel method for the direct synthesis of γ-lactams. We report here the results of the investigation of Wolff rearrangement of several diazoketones derived from N-tosyl protected α-amino acids and β-amino acids. 相似文献
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The reactions of tetraphenylporphine (H2TPP) with copper(II) chelates in DMSO were studied. -Amino acids (glycine, -alanine, valine, leucine, tyrosine, and glutamine) were used as chelating ligands. The study of the reaction kinetics showed that Cu(II) chelates with alanine and the other amino acids are less reactive in these reactions than acetylacetonates, -nitroso--naphtholates, and hydroxyquinolates. The exception is a Cu(II) complex with tyrosine. The relationship between the structure of the above chelates and the rate of their reactions with porphyrin was determined. 相似文献
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The first histidine catalyzed direct aldol reactions of ketones with nitrobenzaldehydes in water and in poly(ethylene glycol) (PEG) were reported. It reveals that histidine is a good aldol catalyst for synthesis of β-hydroxylketones in water and in PEG, giving good to excellent yields of the respective products. Better enantioand regioselectivity were achieved using low molecular weight PEG as the media. The results show that histidine and PEG-200 or -300 may constitute a promising environmentally benign system for asymmetric synthesis of β-hydroxylketones. 相似文献
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ZW Jiao SY Zhang C He YQ Tu SH Wang FM Zhang YQ Zhang H Li 《Angewandte Chemie (International ed. in English)》2012,51(35):8811-8815
Spiro compounds: An organocatalytic asymmetric method for the C?sp?3?H functionalization of the α?position of racemic cyclic ethers has been developed. The transformation, mediated by catalytic amounts of an imidazolidinone and strong acid, involves a tandem 1,5-hydride transfer/cyclization and provides access to a structurally diverse series of chiral spiroethers with high levels of enantioselectivity. 相似文献
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α-Bromomethyl-α,β-unsaturated ketones can be prepared easily by the successive addition of α,β-unsaturated ketones and then aldehydes to B-bromo-9-borabicyclo[3.3.1]nonane. 相似文献
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Metal triflates have been used to catalyze synthesis of β-enamino ketones or pyrroles from amines and 1,3-dicarbonyl or 1,4-dicarbonyl compounds under solvent-free conditions, respectively. Among different metal triflates screened, 0.5 mol% Ga(OTf)3 efficiently promoted the reactions to give excellent yields. In addition, the catalyst could be recovered easily after the reactions and reused without evident loss in activity. 相似文献
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A comparative systematic analysis of the features of Brönsted behavior of pseudo CH acids(according to Eigen's classification) is made. The analysis is based on combined use of experimental data onpK
a, Ggas, logk
D of CH acids (Ggas is the free energy of acid ionization in the gas phase, logk
D isthe logarithm of the rate constant of hydrogen exchange in a protic solvent). The modified nucleophilicKabachnik constants - are applicable to correlations for all the three kinds of acidity of pseudo CH acids. The electrostatic solvation makes an insignificant contribution to variation of pK
a and weakening of the substituent effect in going from the gas phase to dimethyl sulfoxide, and also to differentiation of the kinetic acidity. The coefficient in the Brönsted equation and the ratio between the rate constants in the correlations, which characterize the degree of proton transfer in the reaction transition state, have much in common from the physical viewpoint. The results of correlation analysis, demonstrating intramolecular uniformity of the interactions, are fully consistent with the conclusion made in the previous part of this work about the solvation uniformity of the interactions, resulting in the absence of thermodynamic deviations from the Brönsted relationship. 相似文献
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Main observation and conclusion
Asymmetric hydrogenation reaction is one of the most efficient synthetic methods to form useful chiral compounds for synthetic c... 相似文献
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Focusing on the steric and electronic properties of the resonance-stabilized amidine framework, a cationic metal-bisamidine complex was designed as a conjugated combined Lewis-Br?nsted acid catalyst. The chiral Zn(II)-bisamidine catalyst prepared from the 2,2'-bipyridyl derived bisamidine ligand, ZnCl2, and AgSbF6 promoted asymmetric Mukaiyama aldol reaction of α-ketoester and α,α-disubstituted silyl enol ether to afford the α-hydroxyester having sequential quarternary carbons in good yield, albeit with low enantioselectivity. Addition of 1.0 equivalent of the fluoroalcohol having suitable acidity and bulkiness dramatically increased the enantioselectivity (up to 68% ee). DFT calculations suggested that this additive effect would be caused by self-assembly of the fluoroalcohol on the Zn(II)-bisamidine catalyst. 相似文献