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11.
Experimental and Theoretical Studies on the Rearrangement of 2‐Oxoazepane α,α‐Amino Acids into 2′‐Oxopiperidine β2,3,3‐Amino Acids: An Example of Intramolecular Catalysis 下载免费PDF全文
Dr. Diego Núñez‐Villanueva Dr. M. Ángeles Bonache Laura Lozano Dr. Lourdes Infantes Prof. José Elguero Prof. Ibon Alkorta Prof. M. Teresa García‐López Dr. Rosario González‐Muñiz Dr. Mercedes Martín‐Martínez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2489-2500
Enantiopure β‐amino acids represent interesting scaffolds for peptidomimetics, foldamers and bioactive compounds. However, the synthesis of highly substituted analogues is still a major challenge. Herein, we describe the spontaneous rearrangement of 4‐carboxy‐2‐oxoazepane α,α‐amino acids to lead to 2′‐oxopiperidine‐containing β2,3,3‐amino acids, upon basic or acid hydrolysis of the 2‐oxoazepane α,α‐amino acid ester. Under acidic conditions, a totally stereoselective synthetic route has been developed. The reordering process involved the spontaneous breakdown of an amide bond, which typically requires strong conditions, and the formation of a new bond leading to the six‐membered heterocycle. A quantum mechanical study was carried out to obtain insight into the remarkable ease of this rearrangement, which occurs at room temperature, either in solution or upon storage of the 4‐carboxylic acid substituted 2‐oxoazepane derivatives. This theoretical study suggests that the rearrangement process occurs through a concerted mechanism, in which the energy of the transition states can be lowered by the participation of a catalytic water molecule. Interestingly, it also suggested a role for the carboxylic acid at position 4 of the 2‐oxoazepane ring, which facilitates this rearrangement, participating directly in the intramolecular catalysis. 相似文献
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A series of new heteromultinuclear FeI/RuII clusters are described. The complexes (η6-arene)RuFe2S2(CO)6 (arene = p-cymene 1 , C6Me6 2 ) and Fe2[μ-S (Cp*Ru)(CO)2]2(CO)6 (Cp* = η5-C5Me5) ( 3 ) were prepared by the reduction reactions of (μ-S)2Fe2(CO)6 with 2 equiv of LiHBEt3, followed by treatment (μ-SLi)2Fe2(CO)6 with ruthenium-arene complexes Ru2(μ-Cl)2Cl2(η6-arene)2 or Cp*Ru (CO)2Cl in 22–33% yields. Further reactions of 1 and 2 with 1 equiv of triphenylphosphine in the presence of the decarbonylating agent Me3NO·2H2O, afforded the corresponding monophosphine-substituted FeI/RuII complexes (η6-arene)RuFe2S2(CO)5(Ph3P) (arene = p-cymene 4 , C6Me6 5 ) in 75% and 78% yields. While treatment of parent complex 1 or 2 with 1 equiv of diphosphine Ph2PCH2PPh2 (dppm) in xylene at reflux temperature resulted in the formation of the diphosphine-bridged RuFe2S2(CO)9 derivate RuFe2S2(CO)7(dppm) ( 6 ). The possible pathway for the formation was proposed. Two isomers of novel macrocyclic complexes involve the (η6-arene) Ru-bridged quadruple-butterfly Fe/S clusters [{μ-S (CH2)3S-μ}{(μ-CS2)Fe2(CO)6}2]2[(η6-arene)Ru]2 (arene = p-cymene 7a and 7b , C6Me6 8a and 8b ) were isolated by reactions of two μ-CS2-containing dianion [{μ-S (CH2)3S-μ}{(μ-S=CS)Fe2(CO)6}2]2− with [Ru2(μ-Cl)2Cl2(η6-arene)2], in which the propylene groups are attached to two S atoms by ee and ea types of bonds respectively. All the new complexes 1 – 8 have been characterized by elemental analysis, spectroscopy, and particularly for 1 – 6 , 7b and 8a by X-ray crystallography. In addition, the electrochemical properties of representative complexes 1 – 4 and 6 have been investigated. 相似文献
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Medical treatment and vaccination decisions are often sequential and uncertain. Markov decision process is an appropriate means to model and handle such stochastic dynamic decisions. This paper studies the near‐optimality of a stochastic SIRS epidemic model that incorporates vaccination and saturated treatment with regime switching. The stochastic model takes white noises and color noise into account. We first prove some priori estimates of the susceptible, infected, and recovered populations. Moreover, we establish some sufficient and necessary conditions of the near‐optimality by Pontryagin stochastic maximum principle. Our results show that the two kinds of environmental noises have great impacts on the infectious diseases. Finally, we illustrate our conclusions through numerical simulations. 相似文献
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This paper deals with the chemotaxis-growth system: , , in a smooth bounded domain with zero-flux boundary conditions, where μ, δ, and τ are given positive parameters. It is shown that the solution exponentially stabilizes to the constant stationary solution in the norm of as provided that and any given nonnegative and suitably smooth initial data fulfills , which extends the condition in [8]. 相似文献
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Mathematical Programming - We study the worst-case performance guarantee of locally optimal solutions for the problem of minimizing the total weighted and unweighted completion time on parallel... 相似文献
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Muñoz-Villamizar A. Santos J. Grau P. Viles E. 《Central European Journal of Operations Research》2021,29(4):1219-1230
Central European Journal of Operations Research - Environmental efficiency should not be treated independently of production efficiency. Several studies have demonstrated that lean management can... 相似文献