排序方式: 共有173条查询结果,搜索用时 15 毫秒
41.
Rsuini U. Gutirrez Mayra Hernndez-Montes Aarn Mendieta-Moctezuma Francisco Delgado Joaquín Tamariz 《Molecules (Basel, Switzerland)》2021,26(13)
An efficient synthesis of ketimines was achieved through a regioselective Hg(I)-catalyzed hydroamination of terminal acetylenes in the presence of anilines. The Pd(II)-catalyzed cyclization of these imines into the 2-substituted indoles was satisfactorily carried out by a C-H activation. In a single-step approach, a variety of 2-substituted indoles were also generated via a Hg(I)/Pd(II)-catalyzed, one-pot, two-step process, starting from anilines and terminal acetylenes. The arylacetylenes proved to be more effective than the alkyl derivatives. 相似文献
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Jielin Zhang Eleonora Grandi Haigen Fu Thangavelu Saravanan Laura Bothof Pieter G. Tepper Andy‐Mark W. H. Thunnissen Gerrit J. Poelarends 《Angewandte Chemie (International ed. in English)》2020,59(1):429-435
Aspartic acid derivatives with branched N‐alkyl or N‐arylalkyl substituents are valuable precursors to artificial dipeptide sweeteners such as neotame and advantame. The development of a biocatalyst to synthesize these compounds in a single asymmetric step is an as yet unmet challenge. Reported here is an enantioselective biocatalytic synthesis of various difficult N‐substituted aspartic acids, including N‐(3,3‐dimethylbutyl)‐l ‐aspartic acid and N‐[3‐(3‐hydroxy‐4‐methoxyphenyl)propyl]‐l ‐aspartic acid, precursors to neotame and advantame, respectively, using an engineered variant of ethylenediamine‐N,N′‐disuccinic acid (EDDS) lyase from Chelativorans sp. BNC1. This engineered C–N lyase (mutant D290M/Y320M) displayed a remarkable 1140‐fold increase in activity for the selective hydroamination of fumarate compared to that of the wild‐type enzyme. These results present new opportunities to develop practical multienzymatic processes for the more sustainable and step‐economic synthesis of an important class of food additives. 相似文献
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Lukas Brieger Christian Unkelbach Prof. Dr. Carsten Strohmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(71):17780-17784
The incorporation of heavy alkali metals into substrates is both challenging and essential for many reactions. Here, we report the formation of THF-solvated alkali metal benzyl compounds [PhCH2M ⋅ (thf)n] (M=Na, Rb, Cs). The synthesis was carried out by deprotonation of toluene with the bimetallic mixture n-butyllithium/alkali metal tert-butoxide and selective crystallization from THF of the defined benzyl compounds. Insights into the molecular structure in the solid as well as in solution state are gained by single crystal X-ray experiments and NMR spectroscopic studies. The compounds could be successfully used as alkali metal mediating reagents. The example of caesium showed the convenient use by deprotonating acidic C−H as well as N−H compounds to gain insight into the aminometalation using these reagents. 相似文献
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Dochnahl M Löhnwitz K Pissarek JW Biyikal M Schulz SR Schön S Meyer N Roesky PW Blechert S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(23):6654-6666
A series of symmetrical and unsymmetrical N,N'-disubstituted aminotroponimines (ATIHs) have been prepared. Substituents ranging from linear to cyclic alkyl groups, chelating ethers, and aryl groups were employed. The corresponding aminotroponiminate zinc complexes were then synthesized and characterized by a number of techniques, including by X-ray crystallography. Herein we report on the investigations into their activity in the intramolecular hydroamination of nonactivated alkenes. We also demonstrate that complexes bearing ligands with cyclic alkyl groups show superior activity in a number of selected reactions with functionalized aminoalkenes. 相似文献
46.
Tobisch S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(32):9127-9136
The regulation of ring-substituent diastereoselectivity in the intramolecular hydroamination/cyclisation (IHC) of alpha-substituted aminodienes by constrained geometry CGC-lanthanide catalysts (CGC=[Me(2)Si(eta(5)-Me(4)C(5))(tBuN)](2-)) has been elucidated by means of a reliable DFT method. The first survey of relevant elementary steps for the 1-methyl-(4E,6)-heptadienylamine substrate (1) and the [{Me(2)Si(eta(5)-Me(4)C(5))(tBuN)}Sm{N(TMS)(2)}] starting material (2) identified the following general mechanistic aspects of Ln-catalysed aminodiene IHC. The substrate-adduct 3-S of the active CGC-Ln-amidodiene compound represents the catalyst's resting state, but the substrate-free form 3' with a chelating amidodiene functionality is the direct precursor for cyclisation. This step proceeds with almost complete regioselectivity through exocyclic ring closure by means of a frontal trajectory, giving rise to the CGC-Ln-azacycle intermediate 4. Subsequent protonolysis of 4 is turnover limiting, whilst the ring-substituent diastereoselectivity is dictated by exocyclic ring closure. Unfavourable close interatomic contacts between the substrate's alpha-substituent and the catalyst backbone have been shown to largely govern the trans/cis selectivity. Substituents of sufficient bulk in the alpha-position of the substrate have been identified as being vital for stereochemical induction. The present study has indicated that the diastereoselectivity of ring closure can be considerably modulated. The variation of the lanthanide's ionic radius and introduction of extra steric pressure at the substrate's alpha-position and/or the CGC N centre have been identified as effective handles for tuning the selectivity. The quantification of these factors reported herein represents the first step toward the rational design of improved CGC-Ln catalyst architectures and will thus aid this process. 相似文献
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Tobisch S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(52):14974-14986
The present study comprehensively explores alternative mechanistic pathways for intramolecular hydroamination of 2,2-dimethyl-4-penten-1-amine (1) by [{To(M)}MgMe] (To(M)=tris(4,4-dimethyl-2-oxazolinyl)phenylborate) (2) with the aid of density functional theory (DFT) calculations. A single-step amidoalkene → cycloamine conversion through a concerted proton transfer associated with N-C ring closure has been explored as one possible mechanism; its key features have been described. This non-insertive pathway evolves via a six-centre TS structure featuring activation of the olefin unit towards nucleophilic amido attack outside the immediate vicinity of the metal centre by amino proton delivery and describes a viable mechanistic variant for alkaline-earth metal-mediated aminoalkene hydroamination. However, herein is presented sound evidence for the operation of the Mg-N amido σ-bond insertive mechanism, its turnover-limiting activation barrier is found to be 5.0 kcal mol(-1) lower than for the non-insertive mechanism, for the cyclohydroamination of 2,2-disubstituted 4-aminoalkenes by a [{To(M)}Mg-NHR] catalyst. The operative mechanism involves rapid equilibria of the {To(M)}Mg-amidoalkene resting state 3 with its amine adduct, easily accessible and thermodynamically disfavoured, hence reversible, 1,2-olefin insertion into the Mg-N amido σ-bond with ring closure at 3, linked to turnover-limiting Mg-C azacycle tether aminolysis by an adduct substrate molecule, followed by facile cycloamine liberation to regenerate the active catalyst species 3. The following aspects are in support of this scenario: 1) the derived rate law is consistent with the experimentally obtained empirical rate law; 2) the reasonable agreement between the computationally estimated and the observed value of the primary KIE; 3) the assessed effective activation barrier for turnover-limiting aminolysis matches empirically determined Eyring parameters remarkably well; and 4) the observed resistance of isolated 3 to undergo amidoalkene cycloamine/cycloamido transformation until further quantities of substrate is added is consistently explained. The herein unveiled insights into the structure-reactivity relationships will undoubtedly govern the rational design of alkaline-earth metal-based catalysts and likely facilitate further advances in the area. 相似文献
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Christos E. Kefalidis Constantinos A. Tsipis 《Journal of computational chemistry》2012,33(20):1689-1700
A detailed analysis of the reaction profiles of the hydroamination reaction between ethylene and ammonia catalyzed by the diplatinum(II) [{Pt(NH2)(μ‐H)(PPh3)}2] complex is presented herein using density functional theory computational techniques. The coordinatively unsaturated 14e T‐shaped [Pt(NH2)(PPh3)H] species resulted from the dissociation of the diplatinum [{Pt(NH2)(μ‐H)(PPh3)}2] precatalyst are identified as the active catalytic species. All possible reaction pathways that constitute the entire catalytic cycle have exhaustively been investigated. Overall, the rate‐determining step of all catalytic cycles constructed was found to be the oxidative addition of ammonia that leads to the regeneration of the catalyst. According to the energy span model, the outer‐sphere mechanism for the hydroamination of ethylene with ammonia catalyzed by the diplatinum complexes is favored over the inner‐sphere one, whereas TOF values are in favor of the inner‐sphere mechanism. © 2012 Wiley Periodicals, Inc. 相似文献