A formal synthesis of martinelline via a combination of two types of radical reactions

A formal synthesis of martinelline has been accomplished via two types of radical reactions as the key steps. These are the radical addition-cyclization-elimination of an oxime ether carrying an unsaturated ester and a C-C bond formation through a radical 1,5-hydrogen atom translocation.     

Towards click chemistry: Multicomponent reactions via combinations of name reactions

In this report, we try to show the importance of incorporation of name reactions in the sequential cascade reaction in which significantly decreasing the number of steps towards an ideal and practical multi-step synthesis of natural products as well showing virtually all the advantages already mentioned for “Click Chemistry”. In addition, since the chiral inductions are desired for most of these sequential name reactions, their asymmetric catalyzed reactions were also described.     

tert-Butyl isocyanide revisited as a convertible reagent in the Groebke-Blackburn reaction

tert-Butyl isocyanide can serve as the convertible reagent in Groebke-Blackburn multi-component reactions. The effective removal of the tert-butyl group from the resulting imidazo[1,2-a]azines and -azoles is achieved on a gram scale in two steps without chromatographic purification.     

A DFT study on a mutipathways,one product reaction: Initially divergent radical reactions reconverge to form a single product

The mechanism for initially divergent radical reactions reconverging to form a single product is studied using density functional theory calculations. The calculation results suggest that there are six possible pathways from reactants to products. The free energy barriers of the rate‐determining steps of each pathway are almost equal. Thus, different from usual reaction, the selectivity of this reaction is determined by the relative value of free energy barriers of the two competitive reactions, that is, cyclization and bimolecular trapping, rather than that of rate‐determining steps. In all reaction pathways, cyclization reaction is more competitive than bimolecular trapping reaction due to its low free energy barrier. In addition, the free energy barriers of bimolecular trapping reaction between Bu₃SnH and reactants are all lower than that of NC? C₆H₁₁. However, Bu₃SnH is not always suitable due to its large steric repulsion. © 2014 Wiley Periodicals, Inc.     

A facile approach to the synthesis of securinega alkaloids: stereoselective total synthesis of (−)-allonorsecurinine

A concise stereoselective total synthesis of alkaloid (−)-allonorsecurinine is described utilizing classical reactions such as Grignard, Aldol and Horner-Wittig reactions as the key steps.     

Construction of the reaction networks for heterogeneous catalytic reactions: Fischer—Tropsch synthesis and related reactions

The key approaches to the generation of reaction networks for the synthesis of products from CO and H₂ are considered. The selection rules for the elementary steps on the surface of heterogeneous catalysts are formulated. Data on the surface compounds and steps related to reactions of CO and H₂ are analyzed and a set of transforms (models of elementary steps) for generation of the reaction network are selected. Eight variants of generation of reaction networks for the formation of C1 products with different sets of transforms (12 to 31) were tested in computer experiments, and eight reaction networks comprising 34 substances and 132 to 1647 elementary steps were obtained. The pathways to CO₂, CH₄, and CH₃OH and pairs of compounds CH₄, CO₂ and CH₄, HCOOH obtained from the reaction network (220 elementary steps) are compared with the published schemes.     

Preparation of enantiomerically pure (E)-β-sulfinylenones from β-ketoesters

Enantiomerically pure (E)-β-sulfinylenones are smoothly prepared from β-ketoesters in three steps with good overall yield. Since they can be the substrates of many diastereoselective reactions, they represent versatile precursors of a wide range of chiral building blocks. We propose a rationale to explain the formation of (E)-β-sulfinylenones from the corresponding δ-enol-methylethers.     

A simple metal free highly diastereoselective synthesis of heteroaryl substituted (±) cyclohexanols by a branched domino reaction

A self diastereoselective, simple metal free and efficient branch domino reaction gave multiple heteroaryl substituted (±) cyclohexanols with five chiral centres in >95% yields. The reactions that occur are Claisen Schmidt condensation followed by Michael addition and Aldol reactions of heteroaryl carbaldehydes and acetyl pyridine derivatives. Mechanistic study of the reactions shows excellent self diastereoselectivity (dr > 99%) in the intermediate steps which results selectively in the formation of one set of enantiomers out of sixteen possible enantiomeric pairs. The self diastereoselectivity of reaction in all the steps dominates due to the steric hindrance induced by the bulky heteroaryl groups. The stereochemistry of the synthesized compounds is established using single crystal XRD.     

Short synthesis of bis-NHC-Pd catalyst derived from caffeine and its applications to Suzuki, Heck, and Sonogashira reactions in aqueous solution

A short and efficient synthesis of a bis-NHC-palladium catalyst simply prepared from caffeine in two steps was reported. The air and moisture stable Pd catalyst can be used as a good catalyst in running Suzuki-Miyaura, Mizoroki-Heck, and Sonogashira reactions in aqueous solution.     

Lowering Energy Barriers in Surface Reactions through Concerted Reaction Mechanisms

Any technologically important chemical reaction typically involves a number of different elementary reaction steps consisting of bond‐breaking and bond‐making processes. Usually, one assumes that such complex chemical reactions occur in a step‐wise fashion where one single bond is made or broken at a time. Using first‐principles calculations based on density functional theory we show that the barriers of rate‐limiting steps for technologically relevant surface reactions are significantly reduced if concerted reaction mechanisms are taken into account.     

Ab-Initio Molecular Dynamics Simulation of Condensed-Phase Reactivity: The Electrolysis of Amino Acids and Peptides

Electrolysis is a potential candidate for a quick method of wastewater cleansing. However, it is necessary to know what compounds might be formed from bioorganic matter. We want to know if there are toxic intermediates and if it is possible to influence the product formation by the variation in initial conditions. In the present study, we use Car–Parrinello molecular dynamics to simulate the fastest reaction steps under such circumstances. We investigate the behavior of amino acids and peptides under anodic conditions. Such highly reactive situations lead to chemical reactions within picoseconds, and we can model the reaction mechanisms in full detail. The role of the electric current is to discharge charged species and, hence, to produce radicals from ions. This leads to ultra-fast radical reactions in a bulk environment, which can also be seen as redox reactions as the oxidation states change. In the case of amino acids, the educts can be zwitterionic, so we also observe complex acid–base chemistry. Hence, we obtain the full spectrum of condensed-phase chemistry.     

SurfKin: An ab initio kinetic code for modeling surface reactions

In this article, we describe a C/C++ program called SurfKin (Surface Kinetics) to construct microkinetic mechanisms for modeling gas–surface reactions. Thermodynamic properties of reaction species are estimated based on density functional theory calculations and statistical mechanics. Rate constants for elementary steps (including adsorption, desorption, and chemical reactions on surfaces) are calculated using the classical collision theory and transition state theory. Methane decomposition and water–gas shift reaction on Ni(111) surface were chosen as test cases to validate the code implementations. The good agreement with literature data suggests this is a powerful tool to facilitate the analysis of complex reactions on surfaces, and thus it helps to effectively construct detailed microkinetic mechanisms for such surface reactions. SurfKin also opens a possibility for designing nanoscale model catalysts. © 2014 Wiley Periodicals, Inc.     

A concise and stereoselective total synthesis of L-783,290

A stereoselective total synthesis of L-783,290 has been achieved involving Alder–Rickert reaction, ring closing metathesis, and chemoselective oxidation as key steps. This approach has successfully demonstrated a linear sequence of reactions, which are highly stereoselective for the construction of the resorcylic acid unit.     

A concise and straightforward approach to total synthesis of (+)-Strictifolione and formal synthesis of Cryptofolione via a unified strategy

We describe a concise and straightforward approach to the total syntheses of (+)-Strictifolione and Cryptofolione in the longest linear sequences of four steps and six steps from 3-phenyl propanal and trans-cinnamaldehyde, respectively. The route utilized a titanium tetraisopropoxide/(R)-[1,1'-binaphthalene]-2,2'-diol catalyzed Mukaiyama aldol reaction, indium(0)-promoted Barbier reaction, and olefin cross-metathesis as the key reactions.     

An interpretation of the kinetics of ethylene oxidation over silver based on separate studies of kinetics of the reaction steps

The kinetics of the separate reaction steps, corresponding to the stepwise redox mechanism of ethylene oxidation over silver, was studied. The results are used for the interpretation of the kinetics of overall catalytic reactions by taking into account an influence of the adsorption of oxygen on the surface properties of silver.     

Novel regio- and stereo-selectivity: synthesis of dihydropyrrolo[1,2-f]phenanthridines via isocyanide-based multicomponent reaction

The novel one-pot three-component reactions of the zwitterions generated in situ from three isocyanides and 2-arylidenemalononitriles with phenanthridine via 1,3-dipolar cycloaddition are described. The reactions afforded the corresponding dihydropyrrolo[1,2-f]phenanthridine derivatives in good yields without using any catalyst and activation. The stereochemistry of the final products was confirmed by single-crystal X-ray diffraction analysis.     

基于表面占位效应和合理动力学模型的电催化火山关系

电催化在水电解、燃料电池等能源和环境领域起着至关重要的作用.电催化火山关系是预测和理解催化剂活性趋势的通用和标准工具.N?rskov等提出的基于最大反应自由能(ΔG0max)的现代电催化火山关系理论,由于未充分考虑电极电位、中间体及毒物的表面占位以及溶液pH等对电催化动力学的影响,在高活性催化剂的准确预测方面存在局限....     

Microwave-assisted benzyne-click chemistry: preparation of 1H-benzo[d][1,2,3]triazoles

The benzotriazoles were prepared by three-component and two-component microwave-assisted [3+2] cycloadditions of various azides to benzyne, 3-methoxybenzyne, and 4,5-difluorobenzyne. In the three-component reaction, the aryne is generated, in the presence of an azide prepared in situ, by the reaction of an o-(trimethylsilylaryl) triflate with either CsF or KF/18-Crown-6. However, in the two-component reactions, a freshly prepared azide is added to the reaction vessel prior to aryne generation. Good to excellent yields of benzotriazoles were obtained in 15-20 min when the microwave-assisted reactions were carried out at 125 °C. These reaction times are significantly faster than similar reactions carried out using conventional heating.     

Synthetic studies of venturicidins: stereoselective synthesis of the C15-C27 segment based on two types of stereospecific epoxide opening reactions

The C15-C27 segment of venturicidins was stereoselectively synthesized by using two types of stereospecific methyl substitution reactions of epoxides and subsequent stereocontrolled methylation reactions of lactone derivatives as the key steps.     

BF3·Et2O catalyzed diastereoselective nucleophilic reactions of 3-silyloxypiperidine N,O-acetal with silyl enol ether and application to the asymmetric synthesis of (+)-febrifugine

The asymmetric BF₃·Et₂O catalyzed nucleophilic reactions of 3-silyloxypiperidine N,O-acetal 10 with silyl enol ethers derived from ketones are described. (+)-Febrifugine 1, an antimalarial alkaloid, was successfully synthesized based on this nucleophilic substitution. In addition, N,O-acetal 10 was synthesized from l-benzyl glutamate in 11 steps.