Rasta Resin–PPh3–NBniPr2 and its Use in One‐Pot Wittig Reaction Cascades

A new triarylphosphine–tertiary amine bifunctional polymeric reagent has been prepared and used effectively in a variety of one‐pot Wittig reactions. The design of this reagent resolved a deficiency of a previously reported related material, and allowed it to perform more efficiently in such reactions. Furthermore, it was readily recyclable, and was also successfully applied in cascade processes involving one‐pot Wittig reactions followed by either a conjugate reduction or a reductive aldol reaction. In these reaction cascades, the phosphine oxide groups generated in the Wittig reaction served as the catalyst for the subsequent reaction.     

Formation and reactivity of the addition products of alkoxides and thiolate anions to vinyl selenones

Vinyl selenones react with sodium methanethiolate in methanol to give the product of conjugate addition and subsequent displacement of the selenonyl group. On the contrary, the same reaction carried out with alkoxide anions affords the conjugate addition products in excellent yields. These β-alkoxy alkyl phenyl selenones are stable compounds which can react in several ways with loss of the selenonyl group. Their reactions with MeONa or MeSNa have been investigated both in MeOH and in DMF. The products observed derive from substitution and elimination processes as well as from retro Michael reactions followed by nucleophilic substitution of the vinyl selenone thus generated. These results indicate that the ArSeO₂ is a strong electron attracting group with peculiar properties. Beside making acidic the α-hydrogen atoms it activates the carbon-carbon double bond towards the addition of anionic reagents and it acts as a good leaving group in nucleophilic substitution, both aliphatic and vinylic, and in elimination reactions. The appropriate choice of the reagent and of the solvent allows to direct the reaction towards the desired products. Useful synthetic applications of these reactions are presented.     

Conjugate Addition vs Heck Reaction: A Theoretical Study on Competitive Coupling Catalyzed by Isoelectronic Metal (Pd(II) and Rh(I))

Density functional theory studies have been carried out to investigate the mechanism of the Pd(II)(bpy)- and Rh(I)(bpy)-catalyzed conjugate additions and their competitive Heck reactions involving α,β-unsaturated carbonyl compounds. The critical steps of the mechanism are insertion and termination. The insertion step favors 1,2-addition of the vinyl-coordinated species to generate a stable C-bound enolate intermediate, which then may isomerize to either an oxa-π-allyl species or an O-bound enolate. The termination step involves a competition between β-hydride elimination, leading to a Heck reaction product, and protonolysis reaction that gives a conjugate addition product. These two pathways are competitive in the Pd(II)-catalyzed reaction, while a preference for protonolysis has been found in the Rh(I)-catalyzed reaction. The calculations are in good agreement with the experimental observations. The potential energy surface and the rate-determining step of the β-hydride elimination are similar for both Pd(II)- and Rh(I)-catalyzed processes. The rate-determining steps of the Pd(II)- and Rh(I)-catalyzed protonolysis are different. Introduction of an N- or P-ligand significantly stabilizes the protonolysis transition state via the O-bound enolate or oxa-π-allyl complex intermediate, resulting in a reduced free energy of activation. However, the barrier of the β-hydride elimination is less sensitive to ligands. For the Rh(I)-catalyzed reaction, protonolysis is calculated to be more favorable than the β-hydride elimination for all investigated N and P ligands due to the significant ligand stabilization to the protonolysis transition state. For the Pd(II)-catalyzed reaction, the complex with monodentate pyridine ligands prefers the Heck-type product through β-hydride elimination, while the complex with bidentate N and P ligands favors the protonolysis. The theoretical finding suggests the possibility to control the selectivity between the conjugate addition and the Heck reaction by using proper ligands.     

Mechanisms and Beyond: Elucidation of Fluxional Dynamics by Exchange NMR Spectroscopy

Detailed mechanistic information is crucial to our understanding of reaction pathways and selectivity. Dynamic exchange NMR techniques, in particular 2D exchange spectroscopy (EXSY) and its modifications, provide indispensable intricate information on the mechanisms of organic and inorganic reactions and other phenomena, for example, the dynamics of interfacial processes. In this Review, key results from exchange NMR studies of small molecules over the last few decades are systemised and discussed. After a brief introduction to the theory, the key types of dynamic processes are identified and fundamental examples given of intra- and intermolecular reactions, which, in turn, could involve, or not, bond-making and bond-breaking events. Following that logic, internal molecular rotation, intramolecular stereomutation and molecular recognition will first be considered because they do not typically involve bond breaking. Then, rearrangements, substitution-type reactions, cyclisations, additions and other processes affecting chemical bonds will be discussed. Finally, interfacial molecular dynamics and unexpected combinations of different types of fluxional processes will also be highlighted. How exchange NMR spectroscopy helps to identify conformational changes, coordination and molecular recognition processes as well as quantify reaction energy barriers and extract detailed mechanistic information by using reaction rate theory in conjunction with computational techniques will be shown.     

两亲分子组装介导的化学反应及相关生命起源化学

化学反应会受其所处微环境影响,因此不同分子间相互作用对反应进程的调控不容忽视.水溶液作为优良的反应介质,其应用常受到反应物溶解性差的限制.在水溶液中引入胶束或囊泡等两亲分子组装,可在一定程度上克服这种不足.这些均匀分散的动态组装,提供了有别于本体水溶液的微环境,以非共价的方式,将单体结合到其极性表面或疏水内核.通过加速...     

A kinetic model for pyrolysis of CF2HCl

Thermal decomposition of CF₂HCl has been modeled using 2,269 thermally activated reactions and 63 chemically activated processes. Thermochemical properties for the species involved are calculated using statistical mechanics and group contribution theory, and reaction rate constants are determined using transition state theory. The theoretical predictions, obtained without fitting any parameter values, afree closely with available experimental data. Also, the reactions that control the distribution of reaction products are identified, and this, in turn, permits simplification of the reaction set. Sensitivity studies show that uncertainties in the calculations do not alter the predicted trends in behavior or the main reaction pathways. © 1995 John Wiley & Sons, Inc.     

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.     

Ultrasound-irradiated Michael addition of amines to ferrocenylenones under solvent-free and catalyst-free conditions at room temperature

A facile Michael addition of ferrocenylenones with aliphatic amines under ultrasound irradiation in the absence of solvent and catalyst at room temperature can afford 1-ferrocenyl-3-amino carbonyl compounds rapidly in high yields, which is also efficient in the aza-Michael reaction of other α,β-unsaturated carbonyl compounds such as chalcone, carboxylic ester, etc. However, aromatic amines do not undergo the conjugate addition at all, and the reactions under existing methods do not proceed or take place in low yield after a long reaction time. Apart from experimental simplicity, generality and selectivity, the advantages of this methodology are the rapid, environmentally benign and less expensive processes, which will contribute to the progress of green chemistry.     

Intermediates Formed in the Reactions of Organocuprates with α,β‐Unsaturated Nitriles

Conjugate additions of organocuprates are of outstanding importance for organic synthesis. To improve our mechanistic understanding of these reactions, we have used electrospray ionization mass spectrometry for the identification of the ionic intermediates formed upon the treatment of LiCuR₂ ? LiCN (R=Me, Bu, Ph) with a series of α,β‐unsaturated nitriles. Acrylonitrile, the weakest Michael acceptor included, did not afford any detectable intermediates. Fumaronitrile (FN) yielded adducts of the type Li_n?1Cu_nR_2n(FN)_n^?, n=1–3. When subjected to fragmentation in the gas phase, these adducts were not converted into the conjugate addition products, but re‐dissociated into the reactants. In contrast, the reaction with 1,1‐dicyanoethylene furnished the products of the conjugate addition without any observable intermediates. Tri‐ and tetracyanoethylene proved to be quite reactive as well. The presence of several cyano groups in these substrates opened up reaction pathways different from simple conjugate additions, however, and led to dimerization and substitution reactions. Moreover, the gas‐phase fragmentation behavior of the species formed from these substrates indicated the occurrence of single‐electron transfer processes. Additional quantum‐chemical calculations provided insight into the structures and stabilities of the observed intermediates and their consecutive reactions.     

Asymmetric phase-transfer reactions under base-free neutral conditions

Although quaternary onium salt-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles proceeded smoothly in the presence of lipophilic quaternary onium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate additions, aldol reaction, sulfenylation, and chlorination under the influence of chiral bifunctional onium bromides as key catalysts.     

Electrochemical reactions at the electrode/solution interface:Theory and applications to water electrolysis and oxygen reduction

Theoretical simulations on complex electrochemical processes have been developed on the basis of the understanding in electrochemistry,which has benefited from quantum mechanics calculations.This article reviews the recent progress on the theory and applications in electrocatalysis.Two representative reactions,namely water electrolysis and oxygen reduction,are selected to illustrate how the theoretical methods are applied to electrocatalytic reactions.The microscopic nature of these electrochemical reaction...     

Reactive orbital energy theory serving a theoretical foundation for the electronic theory of organic chemistry

It is established that the reactive orbital energy theory (ROET) theoretically reproduces the rule-based electronic theory diagrams of organic chemistry by a comparative study on the charge transfer natures of typical organic carbon–carbon and carbon–heteroatom bond formation reactions: aldol, Mannich, α-aminooxylation, and isogyric reactions. The ROET, which is an expansion of the reaction electronic theories (e.g., the frontier orbital theory) in terms of orbital energies, elucidates the reactive orbitals driving reactions and the charge transferability indices of the reactions. Performing the ROET analyses of these reactions shows that the charge transfer directions given in the rule-based diagrams of the electronic theory are reproduced even for the functional groups of charge transfer destinations in all but only two processes for 38 reaction processes. The ROET analyses also make clear the detailed orbital-based pictures of these bond formation reactions: that is, the use of the out-of-plane antibonding π orbitals in acidic conditions (enol-mode) and in-plane antibonding π orbitals in basic conditions (enolate-mode), which explain the experimentally assumed mechanisms such as the π-bond formations in acidic conditions and σ-bond formations at α-carbons in basic conditions. Furthermore, the ROET analyses explicate that the methyl group initially accepts electrons and then donates them to the bond formations in the target reactions. It is, consequently, suggested that the ROET serves a theoretical foundation for the electronic theory of organic chemistry.     

L-脯氨酸催化不对称有机反应的研究进展

综述了L-脯氨酸作为有机小分子催化剂在若干不对称有机反应(如Aldol反应,Mannich反应,共轭加成等)中的研究进展.参考文献33篇.     

杂环反铂(Ⅱ)抗癌药物水解反应机理的DFT研究

用DFT-B3LYP方法和IEF-PCM溶剂化模型研究了反铂抗癌药物trans-[PtCl2(piperidine)(Am)](Am=2-picoline(1),3-picoline(2),4-picoline(3)),trans-[PtCl2(piperidine)(piperazine)](4),trans-[PtCl2(pipera-zine)2](5)and trans-[PtCl2(iminoether)2](6)的水解过程.水解反应是药物与DNA靶分子作用的关键活化步骤.全优化和表征了一水解和二水解反应经由一般的SN2路径过程所有物种的势能面稳定点.结果发现反应过程遵循已经建立的平面正方形配合物的配体取代反应理论,即取代反应通常通过一个三角双锥过渡态结构的铂配体交换反应发生.得到的过渡态结构与以前的相关工作一致,所有反应都是吸热反应;所有体系的二水解能垒都高于一水解.与顺铂相比,这些配合物都有更快的水解反应速率;并与以前类似的反铂配合物的研究做了比较.研究结果提供了这些配合物水解反应过程的详细能量变化,对理解药物与DNA靶分子的作用机理和新型反铂抗癌药物的设计有帮助.     

Studies of the Anodic Oxidation of 1,4-Diazabicyclo

The title compound (1) was studied at platinum and gold electrodes in acetonitrile. A reversible oxidation peak occurs at +0.30 V vs the standard potential for ferrocenium ion/ferrocene. This process is followed by a second irreversible anodic peak that is due to the oxidation of the initially formed radical cation to the dication. The principal ultimate product of the first oxidation, the conjugate acid of 1, is also oxidized over the range of potentials corresponding to the second anodic peak. The rate of disappearance of the radical cation of 1 has been determined by cyclic voltammetry. The results are best interpreted in terms of parallel pseudo-first-order decay (k(1) = 0.6 s(-)(1)) and second-order reactions. The first of these second-order reactions is either proton transfer from the radical cation to neutral 1 or hydrogen atom abstraction by the radical cation from neutral 1, reactions that give the same products (k(2) = 100 M(-)(1) s(-)(1)) and are kinetically indistinguishable. The other second-order reaction is the hydrogen-atom-transfer disproportionation of the radical cation giving the conjugate acid of 1 and the immonium ion (k(3) = 100 M(-)(1) s(-)(1)). Both second-order processes must be included to account for the results. The present results are thought to be the first experimental evidence for the occurrence of hydrogen-atom-transfer disproportionation of amine radical cations.     

Some Novel Types of Nitrosugars

The stereochemistry of the reaction of the conjugate base of nitromethane with aldehydosugars was shown to depend on the reaction conditions and the structure of the glycosyl group. Some reactions of a novel type of synthetic intermediates in carbohydrate chemistry, the gem-bromonitroenoses are described.     

The synthesis and stereoselective conjugate addition reactions of α-alkoxyorganocuprate reagents

α-Alkoxyorganocuprate reagents have been prepared from α-alkoxyorganostannanes. The cuprates undergo diastereoselective conjugate addition reactions with cyclohexenone with up to 8:92 selectivity. The effects of trimethylsilyl chloride on the chemical yields and the diastereoselectivity of the reaction are described.     

Pd-NHC catalyzed conjugate addition versus the Mizoroki-Heck reaction

Ace of base: A catalytic system is presented that, solely by choice of the base, selectively switches between conjugate addition and the Mizoroki-Heck reaction of aryl halides with Michael acceptors (see scheme; R, R' = alkyl, aryl). For conjugate addition reactions, this avoids the preparation and use of organometallics.     

Mechanism and stereoselectivity of a dual amino-catalyzed robinson annulation: rare duumvirate stereocontrol

Computational study of the mechanisms and stereoselectivities of a dual amino-catalyzed synthesis of cyclohexenones containing all-carbon γ-quaternary and ?-tertiary stereocenters is reported. Extensive conformational search with density functional theory optimizations, the high-accuracy SCS-MP2/cc-pV∞Z energies, and PCM solvation corrections were used to characterize all intermediates and transition states. Six mechanisms were considered, all consistent with available experiments. The reaction proceeds via sequential Michael and Mannich conjugate additions whereby the primary amine activates the aldehyde and the catalyst activates the pentenone. We have discovered a rare duumvirate stereocontrol: the Michael reaction sets the enantioselectivity, but both the Michael and the Mannich reactions control the diastereoselectivity.     

On the origins of diastereoselectivity in the conjugate additions of the antipodes of lithium N-benzyl-(N-α-methylbenzyl)amide to enantiopure cis- and trans-dioxolane containing α,β-unsaturated esters

"Matching" and "mismatching" effects in the doubly diastereoselective conjugate additions of the antipodes of lithium N-benzyl-(N-α-methylbenzyl)amide to enantiopure cis- and trans-dioxolane containing α,β-unsaturated esters have been investigated. High levels of substrate control were established first upon conjugate addition of achiral lithium N-benzyl-N-isopropylamide to both tert-butyl (S,S,E)-4,5-O-isopropylidene-4,5-dihydroxyhex-2-enoate and tert-butyl (4R,5S,E)-4,5-O-isopropylidene-4,5-dihydroxyhex-2-enoate. However, upon conjugate addition of lithium (R)-N-benzyl-(N-α-methylbenzyl)amide and lithium (S)-N-benzyl-(N-α-methylbenzyl)amide to these substrates, neither reaction pairing reinforced the apparent sense of substrate control. These reactions do not, therefore, conform to the classical doubly diastereoselective "matching" or "mismatching" pattern usually exhibited by this class of reaction. A comparison of these reactions with the previously reported doubly diastereoselective conjugate addition reactions of lithium amide reagents to analogous substrates is also discussed.