The Effect of Pressure on Organic Reactions

The utility of high pressure for the understanding of chemical reactions and its application in organic synthesis is shown for cycloadditions (inter‐ and intramolecular Diels‐Alder reactions, 1,3‐dipolar and [2+2] cycloadditions), cheletropic reactions and pericyclic rearrangements (Cope and Claisen rearrangements and electrocyclizations). The origin of the effect of pressure on chemical reactions is discussed. Especially, the change in the packing coefficient during cyclization of chains and the effect of electrostriction on reactions, in which charged species are generated, contribute substantially to a volume contraction leading to a powerful pressure‐induced acceleration of such reactions. Finally, the effect of pressure on free‐radical reactions (homolytic bond dissociations and quinone oxidations) is described.     

On the mechanisms of cyclic and bicyclic fatty acid monomer formation in heated edible oils

Using recent literature data reporting definite chemical structures for cyclic fatty acid monomers (CFAM), we present new insights into cyclization and rearrangement mechanisms that may be involved in the formation of CFAM and their further transformation into bicyclic fatty acid monomers (BFAM) during the frying process. The existence of structural similarities between CFAM and the unsaturated fatty acids from which they were formed, and between structurally related BFAM and CFAM, led us to examine various possible concerted reactions and thermal rearrangements. These structural similarities as well as the limited number of isomers formed provide evidence for concerted routes that are concordant with all identified structures formed from oleic, linoleic and linolenic acids. The proposed reaction pathways account for the presence of BFAM as well as their most probable structures.     

The Stereochemistry of the Cope Rearrangement: Qualitative Theory (OCAMS) and Computation (AM1)

Contrary to common preconceptions, orbital correlation diagrams can be useful for deducing the mechanism and stereochemistry of degenerate sigmatropic rearrangements. The correlation lines have to be drawn between the reactant and the postulated transition state, rather than between the homomeric reactant and product. In the case of the Cope rearrangment, this is done most economically with Orbital Correspondence Analysis in Maximum Symmetry (OCAMS), by drawing correspondence lines between molecular orbitals of the reactant and those of a formal superposition (STS) of alternative transition structures (TS) in a symmetry point group that includes those of both as subgroups. The alternative boat (C_2v) and chair (C_2h) transition structures postulated for the degenerate Cope rearrangement of 1,5-hexadiene are formally combined to an STS of D_2h symmetry. OCAMS then selects its C_2h component, indicating that the pathway via the chair-like transition state is preferred, in agreement with experimental and computational results for both the Cope rearrangement and the isoelectronic Claisen rearrangement. Rearrangement through the less favored boat pathway is shown to arise from a changed electronic configuration in the transition state. Computational evidence is presented showing that the unexpectedly facile rearrangement of polycyclic molecules like semibullvalene and barbaralane, which are constrained to react via the boat pathway, is primarily due to steric and stereoelectronic factors that are explicable in molecular orbital terms, rather than to the incursion of a biradicaloid transition state.     

Zirconocene and Si-tethered diynes: a happy match directed toward organometallic chemistry and organic synthesis

Characterizing reactive organometallic intermediates is critical for understanding the mechanistic aspects of metal-mediated organic reactions. Moreover, the isolation of reactive organometallic intermediates can often result in the ability to design new synthetic methods. In this Account, we outline synthetic methods that we developed for a variety of diverse Zr/Si organo-bimetallic compounds and Si/N heteroatom-organic compounds through the detailed study of zirconacyclobutene-silacyclobutene fused compounds. Two basic components are involved in this chemistry. The first is the Si-tethered diyne, which owes its rich reactive palette to the combination of the Si-C bond and the C≡C triple bond. The second is the low-valent zirconocene species Cp(2)Zr(II), which has proven very useful in organic synthesis. The reaction of these two components affords the zirconacyclobutene-silacyclobutene fused compound, which is the key reactive Zr/Si organo-bimetallic intermediate discussed here. We discuss the three types of reactions that have been developed for the zirconacyclobutene-silacyclobutene fused intermediate. The reaction with nitriles (the C≡N triple bond) is introduced in the first section. In this one-pot reaction, up to four different components can be combined: the Si-tethered diyne can be reacted with three identical nitriles, with differing nitriles, or with a nitrile and other unsaturated organic substrates such as formamides, isocyanides, acid chlorides, aldehydes, carbodiimides, and azides. Several unexpected multiring, fused Zr/Si organo-bimetallic intermediates were isolated and characterized. A wide variety of N-heterocycles, such as 5-azaindole, pyrrole, and pyrroloazepine derivatives, were obtained. We then discuss the reaction with alkynes (the C≡C triple bond). A consecutive skeletal rearrangement, differing from that observed in the reactions with nitriles, takes place in this reaction. Finally, we discuss the reaction with the C═X substrates (where X is O or N), including ketones, aldehydes, and isocyanides. Oxa- and azazirconacycles are formed via a new skeletal rearrangement. Our results show that the zirconocene and the Si-tethered diyne cooperate as a "chemical transformer" after treatment with various substrates, leading to a diverse range of cyclic Zr/Si organo-bimetallic compounds. This mechanism-derived synthesis of organometallic and organic compounds demonstrates that the investigation of metal-mediated reactions and the isolation of reactive organometallic intermediates not only contribute to the understanding of complex reactions but can also lead to the discovery of synthetically useful methods.     

The combined C-H functionalization/Cope rearrangement: discovery and applications in organic synthesis

The development of methods for the stereoselective functionalization of sp(3) C-H bonds is a challenging undertaking. This Account describes the scope of the combined C-H functionalization/Cope rearrangement (CHCR), a reaction that occurs between rhodium-stabilized vinylcarbenoids and substrates containing allylic C-H bonds. Computational studies have shown that the CHCR reaction is initiated by a hydride transfer to the carbenoid from an allyl site on the substrate, which is then rapidly followed by C-C bond formation between the developing rhodium-bound allyl anion and the allyl cation. In principle, the reaction can proceed through four distinct orientations of the vinylcarbenoid and the approaching substrate. The early examples of the CHCR reaction were all highly diastereoselective, consistent with a reaction proceeding via a chair transition state with the vinylcarbenoid adopting an s-cis conformation. Recent computational studies have revealed that other transition state orientations are energetically accessible, and these results have guided the development of highly stereoselective CHCR reactions that proceed through a boat transition state with the vinylcarbenoid in an s-cis configuration. The CHCR reaction has broad applications in organic synthesis. In some new protocols, the CHCR reaction acts as a surrogate to some of the classic synthetic strategies in organic chemistry. The CHCR reaction has served as a synthetic equivalent of the Michael reaction, the vinylogous Mukaiyama aldol reaction, the tandem Claisen rearrangement/Cope rearrangement, and the tandem aldol reaction/siloxy-Cope rearrangement. In all of these cases, the products are generated with very high diastereocontrol. With a chiral dirhodium tetracarboxylate catalyst such as Rh(2)(S-DOSP)(4) or Rh(2)(S-PTAD)(4), researchers can achieve very high levels of asymmetric induction. Applications of the CHCR reaction include the effective enantiodifferentiation of racemic dihydronaphthalenes and the total synthesis of several natural products: (-)-colombiasin A, (-)-elisapterosin B, and (+)-erogorgiaene. By combining the CHCR reaction into a further cascade sequence, we and other researchers have achieved the asymmetric synthesis of 4-substituted indoles, a new class of monoamine reuptake inhibitors.     

硫酰氟的制备及在有机合成中的应用

硫酰氟作为广谱的熏蒸剂和杀虫剂,性能优异,应用较为广泛.而其独特的物理化学性质,在有机合成化学中的应用近年来也被相继报道.通过对硫酰氟物理化学性质进行介绍,并且对合成硫酰氟的方法、生产情况进行了简要的总结归纳,同时对以硫酰氟作为反应物及化学反应中间体,在有机合成中用于构建磺酰氟、烷基胺、脱氢化等应用进行介绍.期望通过硫...     

Synthesis of Cryptochiral (R,R)-2,3-Dideuterooxirane as Stereochemical Reference Compound and Chemical Correlation with D-(+)-Glyceraldehyde

Chirality plays a pivotal role in chemistry and biology, e.g., structure-specific targeting in drug development or the lock-and-key theory of enzyme interactions. Determining absolute configurations of chiral molecules is essential to understanding such mechanisms and to developing chemical processes involving chiral compounds. In particular, this becomes obvious in the understanding of chemical reaction networks in the context of the origins of life. A stereochemical reference compound that can be correlated with sugars, amino acids, etc. is of great interest. Here, we present the synthesis of enantiopure (R,R)-2,3-dideuterooxirane, of which the absolute configuration has been unambiguously determined by foil-induced Coulomb explosion imaging, and the correlation with the configuration of D-(+)-glyceraldehyde.     

盐酸替罗非班的合成研究

以4-(4-哌啶基)-1-氯丁烷、L-酪氨酸等为原料经过7步反应得到盐酸替罗非班。此合成路线操作简易,总收率达21.6%,中间体及最终产物结构均经过MS和1H NMR确证。     

Quantum chemical studies of zeolite proton catalyzed reactions

Theoretical chemistry applied to zeolite acid catalysis is becoming an important tool in the understanding of the adsorption and interaction of guest molecules with the zeolitic lattice. Especially the understanding of the mechanisms by which zeolite catalyzed chemical reactions proceed becomes possible. It is shown here that the old interpretation of carbonium and carbenium ions as intermediates for zeolite catalyzed reactions has to be replaced by a new approach in terms of positively charged transition states that are strongly stabilized by the zeolitic lattice. The large deprotonation energy of the acidic zeolite is overcome by stabilization of the intermediate or transition state positive charge by the negative charge left in the lattice. The zeolitic sites responsible for the adsorption and/or reaction of guest molecules are the Brønsted-acid and Lewis-base sites. We also show that different transition states are responsible for different kinds of reactions, such as cracking, dehydrogenation, etc.     

几种典型的选择性烷基化反应在精细化工中的应用

本文概述了三种典型的烷基化反应的特点及其研究进展,重点介绍了它们在精细化工中的重要性和应用情况。指出芳香族化合物、苯酚及吡嗪类化合物的选择性烷基化反应是精细化学品化学研究的重要方向,并分析了它们在选择性烷基化反应方面存在的问题和解决方法。     

The chemistry and physics of coking

The causes of coke formation during petroleum refining are only now beginning to be understood. They are closely related to the mechanism of the thermal decomposition of the petroleum Constituents and to changes in the character of the liquid medium. It was formerly believed that coke formation was, a polymerization reaction whereupon the chemical precursors to coke immediately formed macromolecules when subject to the processing temperatures. This is not so. And it is the initial stages of the thermal decomposition which determine the ultimate path of the reaction. Coke formation is a complex process involving both chemical reactions and thermodynamic behavior. Reactions that contribute to this process are cracking of side chains from aromatic groups, dehydrogenation of naphthenes to form aromatics, condensation of aliphatic structures to form aromatics, condensation of aromatics to form higher fused-ring aromatics, and dimerization or oligomerization reactions. Loss of side chains always accompanies thermal cracking, and dehydrogenation and condensation reactions are favored by hydrogen deficient conditions.     

Mechanisms of hydrocarbon conversion reactions on heterogeneous catalysts: analogies with organometallic chemistry

Catalysis is central to most industrial processes for chemical manufacturing. As catalytic processes have become more complex and more demanding, selectivity has become the central issue in their design. Selectivity is defined by the relative rates of competing reaction pathways available to crucial intermediates, and can be controlled by subtle changes in the nature of the catalyst, the reactants, and/or the reaction conditions. In order to be able to do this in a systematic manner, a good understanding of the catalytic reaction mechanisms is needed. Here a connection is drawn between the key elementary steps comprising hydrocarbon conversion reactions on surfaces and those known to occur on discrete organometallic complexes. This way, the hydrogenation, dehydrogenation, hydrogenolysis, chain growth, and isomerization reactions typical in heterogeneous catalysis are redefined in terms of hydride elimination, oxidative addition, reductive elimination, migratory insertion, and 1, 2-shift elementary steps, among others. It is suggested that the knowledge already available from organometallic chemistry can be used to further advance the understanding of the surface science involved in heterogeneous catalysis. Thanks to the commonality of the chemistry involved, a better synergy could also be established between homogeneous and heterogeneous catalytic development. These ideas are discussed in this article in a critical and personal way.*Invited contribution to the special volume entitled The Interface between Heterogeneous and Homogeneous Catalysis, stemming from contributions at the recent International Symposium on Relations between Heterogeneous and Homogeneous Catalysis, and dedicated to the memory of Robert L. Burwell.     

The impact of surface science on the commercialization of chemical processes

Surface science developed instruments for atomic- and molecular-scale studies of catalyst surfaces, their composition and structure, both in a vacuum and at high pressures, under reaction conditions (bridging the pressure gap). Surfaces ranging from single crystals, nanoparticles and thin films to porous high surface area catalytic materials have been studied. Classes of surface structure sensitive and insensitive reactions have been identified by surface science studies, including ammonia synthesis, hydrodesulfurization, reforming, combustion and hydrogenation. Rates of reactions often vary by orders of magnitude between using the right and the wrong surface structures. The roles of many promoters that modify the catalyst surface structures and bonding of adsorbates have been verified. Surface reaction intermediates could be identified and the mobility of adsorbates and the adsorbate induced reconstruction of the catalysts attest to the dynamic nature of the catalytic systems during the reaction turnover. The important active sites for catalysis include the low coordination surface step, kink, oxygen and chloride ion vacancies sites and sites at oxide-metal interfaces. Uncovering the molecular ingredients of heterogeneous catalysts will have a major impact on the understanding of reaction selectivity to help the evolution of green chemistry and selective reaction of many types.     

用于合成叔胺的脂肪族环氧化物的合成

随着我国裂解制乙烯的工业不断壮大,副产物C4烯烃的产量大幅提高,如何有效利用大量生产的C4烯烃是我国亟待解决的问题。实验组以省部级项目"C4烯烃叠合生产高碳烯烃关键技术开发"为背景,研究C4烯烃下游产品的开发利用。本课题以烯烃环氧化胺化路线合成叔胺,主要研究高碳烯烃在胺化过程中环氧化物的合成,将C4烯烃最终转化到精细化工领域,在有效的解决我国大量C4烯烃的同时,提高了精细化工产品的利用率。烯烃的环氧化物在有机化学中应用广泛,它即可以做一些有机合成反应的中间体,也可以作为有机原料,在有机合成,如药物、精细产品、高分子化合物的合成方面应用非常广泛。因此,烯烃环氧化胺化路线不仅可以实现烯烃到脂肪胺的转化,还可以拓宽高碳烯烃的有效利用途径。     

Theoretical Studies of Species Related to Acrolein Hydrogenation

Abstract  

Unsaturated alcohols, usually produced from selective hydrogenation of unsaturated aldehydes, are important fine chemical intermediates used to synthesize pharmaceuticals and flavoring materials. Acrolein, the smallest member in α, β-unsaturated aldehydes, is the model system for studying selective hydrogenation of α, β-unsaturated aldehydes. So far most theoretical work is about adsorption and reactions of acrolein and its related species on surfaces. In the present paper we systematically studied the geometries, electronic structures, stability and transformation of various species derived from stepwise hydrogenation of acrolein in the gas phases. We identified the most stable intermediates for each system and determined the energy barrier for intermolecular conversion between isomers for various species with different content of hydrogen. All these results are valuable and informative for understanding the surface chemistry of hydrogenation of α, β-unsaturated aldehydes.     

Externally stimulated click reactions for macromolecular syntheses

Over the last decade, click chemistry reactions, that are fast, simple to use, easy to purify, versatile, regiospecific, and give high product yields have gained significant importance for synthetic chemistry. The design of these synthetic tools that can be controlled by external stimuli such as microwave, ultrasound, light or electric pulses is a research area with strong interest for modern chemistry. In this contribution, the potential of externally stimulated click reactions in the preparation of various macromolecular structures are discussed along with the selected examples. Considering classical click reactions, external stimulation provides a number of advantages and goals, such as programmable synthesis and precise control over complex and multicomponent systems. Furthermore, these click reactions bring some improvements or overcome existing problems of present click reactions, such as toxicity, irreversible oxidation of catalyst and lack of spatiotemporal control over the reaction initiation. Due to these features, externally stimulated click reactions have various applications in a wide variety of research areas, including materials sciences, polymer chemistry, and pharmaceutical science. The next generation click reactions enable chemists to finally harness available chemical diversity for the sequence-programmable synthesis and modification of macromolecular materials.     

Catalysis of stannane-mediated radical chain reactions by benzeneselenol

The discovery and development of the catalysis of stannane-mediated radical chain reactions by benzeneselenol, generated in situ by reduction of diphenyl diselenide with tributyltin hydride, are described. The catalytic sequence is discussed in terms of polarity reversal catalysis of radical chain reactions, and applications to synthesis are presented. These include the prevention of numerous radical rearrangement reactions, the ability to intervene in certain multistep radical rearrangements, especially aryl and vinyl radical cyclizations, at intermediate stages with advantages to the product profile, and the effective trapping of allyl-, benzyl-, and cyclohexadienyl-type radicals, permitting inter alia the isolation of aryl cyclohexadienes and their application in synthesis.     

Critical perspective: named reactions discovered and developed by women

Named organic reactions. As chemists, we're all familiar with them: who can forget the Diels-Alder reaction? But how much do we know about the people behind the names? For example, can you identify a reaction named for a woman? How about a reaction discovered or developed by a woman but named for her male adviser? Our attempts to answer these simple questions started us on the journey that led to this Account. We introduce you to four reactions named for women and nine reactions discovered or developed by women. Using information obtained from the literature and, whenever possible, through interviews with the chemists themselves, their associates, and their advisers, we paint a more detailed picture of these remarkable women and their outstanding accomplishments. Some of the women you meet in this Account include Irma Goldberg, the only woman unambiguously recognized with her own named reaction. Gertrude Maud Robinson, the wife of Robert Robinson, who collaborated with him on several projects including the Piloty-Robinson pyrrole synthesis. Elizabeth Hardy, the Bryn Mawr graduate student who discovered the Cope rearrangement. Dorothee Felix, a critical member of Albert Eschenmoser's research lab for over forty years who helped develop both the Eschenmoser-Claisen rearrangement and the Eschenmoser-Tanabe fragmentation. Jennifer Loebach, the University of Illinois undergraduate who was part of the team in Eric Jacobsen's lab that discovered the Jacobsen-Katsuki epoxidation. Keiko Noda, a graduate student in Tsutomu Katsuki's lab who also played a key role in the development of the Jacobsen-Katsuki epoxidation. Lydia McKinstry, a postdoc in Andrew Myers's lab who helped develop the Myers asymmetric alkylation. Rosa Lockwood, a graduate student at Boston College whose sole publication is the discovery of the Nicholas reaction. Kaori Ando, a successful professor in Japan who helped develop the Roush asymmetric alkylation as a postdoc at MIT. Bianka Tchoubar, a critically important member of the organic chemistry community in France who developed the Tiffeneau-Demjanov rearrangement. The accomplishments of the women in this Account illustrate the key roles women have played in the discovery and development of reactions used daily by organic chemists around the world. These pioneering chemists represent the vanguard of women in the field, and we are confident that many more of the growing number of current and future female organic chemists will be recognized with their own named reactions.     

基因组再造与重排构建细胞工厂

细胞工厂能利用微生物细胞制备人类所需能源、药物和化学品。底盘细胞和外源代谢路径的适配是构建高效细胞工厂的核心难题。基因组再造指利用化学合成的核苷酸分子“自下而上”构建生物基因组,基因组诱导重排指通过在全基因组尺度进行DNA序列与结构的人为调控。基因组再造和诱导重排实现了对生命体的创造,增强了模式底盘细胞的遗传稳定性和操作柔性。基因组的适度精简和密码子简化改善细胞对底物、能量的利用效率,提高细胞生理性能的预测性和可控性。基因组重排可诱导染色体发生随机删除、复制、移位和倒置等结构变异,可产生大量性状优良的模式底盘细胞,进而加速代谢路径优化,提高路径和底盘细胞的适配性,为人工细胞工厂快速构建和优化提供了新策略。     

Propane Aromatization over HZSM‐5 and Ga/HZSM‐5 Catalysts

The selective transformation of light alkanes to aromatics that are more valuable and versatile feedstocks for the chemical industry is one of the major challenges of catalytic chemistry. The complexity of the aromatization chemistry makes it difficult to unravel reaction mechanisms and, mechanistic information is largely developed from observed product distributions. This article reviews the current mechanistic understanding for the conversion of propane to aromatic compounds over HZSM‐5 and Ga/HZSM‐5 catalysts based on experimental as well as theoretical studies.

Following a general discussion of acidity and confinement effects in these systems, this review focuses on understanding specific reactions occurring on Brønsted acid sites in HZSM‐5. Mechanistic details available from Density Functional Theory (DFT) calculations, as well as kinetic modeling efforts for various complex hydrocarbon systems are critically reviewed. A detailed, tabulated review of the literature compares the catalytic performance of gallium modified ZSM‐5 catalysts and subsequently the promotional effect of gallium as an additive is critically discussed in terms of the nature of the active sites, as well as the new reaction pathways introduced by gallium addition.