Author: Youliang Wang
Publisher:
ISBN: 9781369340693
Category :
Languages : en
Pages : 241
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Book Description
Despite the tremendous advance in homogeneous gold catalysis in the past decade or so, the functionalization of unactivated C(sp3)-H bonds, a highly desirable and yet challenging streamlining synthetic strategy, has so far rarely been realized in this 'gold rush'. My graduate work was focused on the development of new strategies of gold catalysis to access highly reactive gold intermediates and harness their reactivities in insertion into unactivated C(sp3)-H bonds. Three approaches are discussed in this dissertation: (1) via gold vinylidenes: fully functionalized gold vinylidenes generated from simple TMS-terminated alkynones facilely insert into unactivated alkyl groups to furnish versatile 2-bromocyclopentenones; (2) via 'gold benzyne': gold-catalyzed cycloisomerizations of enediynes provide access to hypothetical 'gold benzyne' species, which exhibit reactivities distinctively different from transition metal-free benzynes, including insertions into unactivated C(sp3)-H bonds and regiospecific nucleophilic additions; (3) via oxidatively generated gold carbene: gold carbenes generated upon the oxidation of alkynones are demonstrated for the first time to be capable of inserting into unactivated C(sp 3)-H bonds to yield cylcopentanones and cyclobutanones.
Author: Andrei K. Yudin
Publisher: John Wiley & Sons
ISBN: 3527633405
Category : Science
Languages : en
Pages : 541
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Book Description
Written by an experienced editor widely acclaimed within the scientific community, this book covers everything fromo9xygen to nitrogen functionalities. From the contents: Palladium-Catalyzed Syntheses of Five-Member Saturated Heterocyclic and of Aromatic Heterodynes Palladium-Catalysis for Oxidative 1, 2-Difunctionalization of Alkenes Rhodium-Catalyzed Amination of C-H-Bonds Carbon-Heteroatom Bond Formation by RH(I)-Catalyzed Ring-Opening Reactions Transition Metal-Catalyzed Synthesis of Lactones and of Monocyclic and Fused Five-Membered Aromatic heterocycles the Formation of Carbon-Sulfur and Carbon-Selenium bonds by Substitution and Addition reactions catalyzed by Transition Metal Complexes New Reactions of Copper Acetylides Gold Catalyzed Addition of Nitrogen, Sulfur and Oxygen Nucleophiles to C-C Multiple Bonds. The result is an indispensable source of information for the Strategic Planning of the Synthetic routes for organic, catalytic and medicinal chemists, as well as chemists in industry.
Author: Antoine Simonneau
Publisher: Springer
ISBN: 9783319360973
Category : Science
Languages : en
Pages : 0
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Book Description
Antoine Simonneau's thesis highlights the development of new cycloisomerization reactions through the activation of alkynes with gold complexes. First Simonneau describes 1,6-enynes and their direct conversion into allenes through 1,5-hydride or ester migration processes. The author and his team used appropriate propargylic functional groups to achieve this conversion. This study shows that O-tethered 1,6-enynes carrying a strained cycloalkane at the propargylic position could undergo a cyclopropanation/ring expansion cascade reaction. The author employed this rearrangement as the starting point in the design of a new macro cycle synthesis. The next part of the thesis focuses on the cycloisomerization of diynes involving as the first step of the process the rearrangement of one alkyne partner into an allene thanks to a gold-catalyzed 1,3-shift of a propargylic ester. The thesis discloses a new cycloisomerization pattern featuring a 1,5-carbonyl transfer, giving rise to unprecedented cross-conjugated diketones. In the final part of the research, Simmoneau investigates the gold-catalyzed cycloisomerization mechanism of 1,6-enynes and questions the intermediacy of gold acetylides. By the means of NMR and mass spectrometry analysis, theoretical treatment and solution experiments, it was possible to rule out the involvement of these species in the catalytic cycle. This thesis has led to a number of publications in high-impact journals.
Author: Takahiko Akiyama
Publisher: John Wiley & Sons
ISBN: 1119736412
Category : Science
Languages : en
Pages : 798
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Book Description
Catalytic Asymmetric Synthesis Seminal text presenting detailed accounts of the most important catalytic asymmetric reactions known today This book covers the preparation of enantiomerically pure or enriched chemical compounds by use of chiral catalyst molecules. While reviewing the most important catalytic methods for asymmetric organic synthesis, this book highlights the most important and recent developments in catalytic asymmetric synthesis. Edited by two well-qualified experts, sample topics covered in the work include: Metal catalysis, organocatalysis, photoredox catalysis, enzyme catalysis C–H bond functionalization reactions Carbon–carbon bond formation reactions, carbon–halogen bond formation reactions, hydrogenations, polymerizations, flow reactions Axially chiral compounds Retaining the best of its predecessors but now thoroughly up to date with the important and recent developments in catalytic asymmetric synthesis, the 4th edition of Catalytic Asymmetric Synthesis serves as an excellent desktop reference and text for researchers and students, from upper-level undergraduates all the way to experienced professionals in industry or academia.
Author: Ramesh Giri
Publisher:
ISBN:
Category : Catalysis
Languages : en
Pages : 1280
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Book Description
Carbon-hydrogen (C-H) bonds are ubiquitous in organic molecules. Utilization of such abundant chemical moieties as functional group equivalents could shorten route to synthetic targets and provide chemists with new disconnections in retrosynthesis. As such regio- and stereoselective functionalization of unactivated C-H bonds has remained one of the major challenges in organic chemistry. The majority of the transition metals have been rigorously examined for their efficacy in transforming unactivated C-H bonds (pKa >35) into useful functional groups or into C-C bonds. Among those metals, palladium is particularly effective in activating both aromatic (sp2) and aliphatic (sp3) C-H bonds. This thesis explores the reactivity of palladium catalysts in both of these areas. The research herein was conducted using directing groups for C-H cleavage with special focus on utilizing simple functionality such as carboxylic acids. Chapter one details different types of directing groups and their utility in a variety of reactions. Chapters two and three contain details of research on C-heteroatom (C-I and C-O) and C-C bond formation, respectively, with palladium acetate as a catalyst. The iodination and acetoxylation reactions proceed under mild conditions and moderate to excellent levels of diastereoselectivity (up to 99.9%) have been observed with both sp2 and sp3 C-H bonds using oxazoline as the directing group. Mechanistic investigations have been carried out in order to understand the high level of stereoselection and, in this process, a number of palladacycle intermediates have been characterized by X-ray crystallography which led us to assign the absolute stereochemistry of C-H activation. Moreover, the iodination protocol could also be extended to prepare diiodides as intermediates for cyclopropanation which provides a new disconnection approach to construct cyclopropanes. Chapter two discusses C-C bond formation via cross-coupling reactions with organoboron reagents and carbon monoxide using the carboxylic acids as the directing group. Detailed mechanistic investigation along with characterization of intermediate palladacycle formed from sodium toluate have revealed an unprecendented directing ability of carboxylate groups in which the carbonyl oxygen, rather than the O-anion, directs palladium for C-H cleavage.
Author: LeGrande M. Slaughter
Publisher: Springer
ISBN: 3319137220
Category : Science
Languages : en
Pages : 292
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Book Description
The series Topics in Current Chemistry presents critical reviews of the present and future trends in modern chemical research. The scope of coverage is all areas of chemical science including the interfaces with related disciplines such as biology, medicine and materials science. The goal of each thematic volume is to give the non-specialist reader, whether in academia or industry, a comprehensive insight into an area where new research is emerging which is of interest to a larger scientific audience. Each review within the volume critically surveys one aspect of that topic and places it within the context of the volume as a whole. The most significant developments of the last 5 to 10 years are presented using selected examples to illustrate the principles discussed. The coverage is not intended to be an exhaustive summary of the field or include large quantities of data, but should rather be conceptual, concentrating on the methodological thinking that will allow the non-specialist reader to understand the information presented. Contributions also offer an outlook on potential future developments in the field. Review articles for the individual volumes are invited by the volume editors. Readership: research chemists at universities or in industry, graduate students.
Author: Nathan David Shapiro
Publisher:
ISBN:
Category :
Languages : en
Pages : 596
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Book Description
Historically, chemists have been motivated by problems in total synthesis or by a desire to develop reactions of broad utility. In answer to these challenges, several approaches to fundamental research have been developed. In chapter 1, we describe how our reactivity-driven approach has led to the discovery of numerous synthetic tools. The development of new synthetically useful methodology often rests on an understanding of the mechanistic underpinnings of the desired transformation. This is particularly true when this knowledge forms the basis for subsequent mechanistic proposals. The coordination of an alkyne to a cationic Au(I) complex represents the prototypical mechanistic starting place for many Au(I)-catalyzed reactions. In chapter two, we describe the isolation and characterization of a gold(I)-coordinated alkyne. The crystal structure of this compound is compared to related Ag(I) and Cu(I) compounds. With these structures in hand, we can begin to understand the unique ability of Au(I) complexes to serve as effective %pi;-activation catalysts, especially in understanding why gold is often more effective than copper or silver. In addition to being able to activate %pi;-bonds toward nucleophilic attack, it has been proposed that gold is also capable of stabilizing adjacent carbocations. Such species (i.e. [L-Au-CR2]+) have been referred to as gold-carbenoids or gold-stabilized carbocations. In chapter 3, we describe a bonding model for these intermediates that suggests that while the gold-carbon bond order is generally less than or equal to one, this bond includes both %sigma;- and %pi;-type bonding. Furthermore, the position of a given Au-stabilized intermediate on a continuum ranging from gold-stabilized singlet carbene to gold-coordinated carbocation is dictated by both the carbene substituents and the ancillary ligand. This model provides an explanation for observed ancillary ligand effects and should enable more efficient reaction optimization. In chapter 4, a series of gold(I)-catalyzed rearrangement reactions of alkynyl sulfoxides, sulfimides and sulfur ylides are reported. Homopropargyl sulfoxides are rearranged to benzothiepinones or benzothiopines, while %alpha;-thioenones are formed in the reaction of propargyl sulfoxides. It is proposed that these reactions proceed via an %alpha;-carbonyl gold-carbenoid intermediate formed through gold-promoted oxygen atom transfer from sulfoxide to alkyne. In chapter 5, the development of a convenient gold(III)-catalyzed synthesis of azepines from the intermolecular annulation of propargyl esters and %alpha;, %beta;-unsaturated imines is discussed. Mechanistic experiments suggest that this formal [4 + 3]-cycloaddition reaction proceeds via a stepwise process involving intermolecular trapping of a gold-carbenoid intermediate and subsequent intramolecular trapping of the resulting allyl-gold intermediate. In chapter 6, we discuss the gold(III)-catalyzed [3+3]-cycloaddition reaction of propargyl esters and azomethine imines. This reaction provides a rapid entry into a wide range of substituted tetrahydropyridazine derivatives from simple starting materials. A mechanism similar to that proposed in chapter 5 is discussed, along with a detailed description of the consequences of this mechanism on the diastereoselectivity of the annulation reaction. In addition, a strategy for rendering this reaction asymmetric is presented.
Author: Pierre H. Dixneuf
Publisher: Springer
ISBN: 3319246305
Category : Science
Languages : en
Pages : 269
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Book Description
The series Topics in Organometallic Chemistry presents critical overviews of research results in organometallic chemistry. As our understanding of organometallic structure, properties and mechanisms increases, new ways are opened for the design of organometallic compounds and reactions tailored to the needs of such diverse areas as organic synthesis, medical research, biology and materials science. Thus the scope of coverage includes a broad range of topics of pure and applied organometallic chemistry, where new breakthroughs are being achieved that are of significance to a larger scientific audience. The individual volumes of Topics in Organometallic Chemistry are thematic. Review articles are generally invited by the volume editors. All chapters from Topics in Organometallic Chemistry are published OnlineFirst with an individual DOI. In references, Topics in Organometallic Chemistry is abbreviated as Top Organomet Chem and cited as a journal.
Author: Malina Michalska
Publisher:
ISBN:
Category :
Languages : en
Pages : 68
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Book Description
The research project is centred on the development of new gold catalyzed transformations in N-acyliminium ion chemistry. The objective of our first part of the project is to develop an enantioselective gold-catalyzed 5 exo-dig intramolecular hydroalkoxylation/aza-Ferrier-Petasis rearrangement sequence. This sequence could give an asymmetric and atom economic expeditious access to the structure of hydropyrrolizidines, which are known to be potential biologically active compounds. A second part of the project is devoted to the development of the first catalytic alkynylation of cyclic N-acyliminium ions using N,O-acetals. This type of reaction is potentially an important transformation, giving rise to propargylic amine derivatives amenable to further interesting synthetic manipulations en route to nitrogen-containing natural products and some analogs. Considering our objectives, key features is the use of TMS alkynes in conjunction with gold complexes that have been paired with poorly nucleophilic counter-ions. To broaden the scope of catalysis based on gold, it is important to extend the range of substrates and functional groups that can be activated by gold complexes. A final section is devoted to the sequential catalysis which designs the promotion of catalytic multistep processes. In this way, two fundamentally distinct chemical transformations are catalytically promoted in a single flask. This research area allows the rapid and efficient reach of complex molecular frameworks with improved yields and resource efficiency. Therefore, this is an exciting theme in modern organic synthesis that has recently stimulated the report of numerous excellent contributions.
Author: Aaron D. Lackner
Publisher:
ISBN:
Category :
Languages : en
Pages : 534
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Book Description
Abstract Development of Gold-Catalyzed Oxidative Alkene Heteroarylation and of Enantioselective Reactions Enabled by Phase Separation by Aaron Daniel Lackner Doctor of Philosophy in Chemistry University of California, Berkeley Prof. F. Dean Toste, Chair As with many bodies of research compiled through the course of a graduate career, this thesis reflects an uneven progression of aim based on the accumulation of unexpected results. Three main topics will be discussed in this thesis' chapters that may appear somewhat disparate. In particular, a significant conceptual gap exists between the first topic, oxidative gold catalysis, and the second topic, chiral anion phase-transfer catalysis. However, these fields are united by the realization that the characteristics of a reagent integral to the former might also be uniquely suitable for implementation in the latter. Chapter 1 discusses the development of a redox-active Au(I)-Au(III) catalytic system for the functionalization of alkenes. Based on early precedent, we hoped to show that the strong dicationic oxidant Selectfluor could generate a catalytically active cationic Au(III) center that enables reactivity that cannot be achieved through Au(I) catalysis, terminating in an arylation rather than protonation to return the catalyst. Methods for the intra- and intermolecular heteroarylation of alkenes were developed and experiments were performed suggesting an unusual reaction mechanism. Attempts to expand the types of transformations that could be accomplished under this mode of reactivity unexpectedly led us to consider instead the properties of Selectfluor and how it could be effectively employed as a reagent in enantioselective transformations. Chapter 2 addresses this very topic. The dicationic nature of the electrophilic fluorination reagent Selectfluor imparts on it many favorable qualities, but solubility in organic solvents is not one of them. Using a concept developed earlier within our laboratories, we hoped to show that this insolubility could be used to suppress racemic background reaction in enantioselective fluorination reactions, a class of transformation that remains largely underdeveloped in the literature. Lipophilic chiral phosphate anions, which can undergo anion exchange with the reagent salt, serve to solubilize the cationic fluorinating agent, rendering it both chiral and available for reaction with a suitable substrate. This mode of reactivity, chiral anion phase-transfer catalysis, was used to develop the enantioselective fluorocyclization of alkenes. Studies in the use of another type of cationic electrophile for the enantioselective oxidation of alcohols will also be discussed. An extension of the concept of phase-separation for suppression of unwanted reactivity was applied to the deracemization of chiral amines, which is presented in Chapter 3. Single-operation deracemization, in which a racemic substrate is dynamically resolved to its enantioenriched form, generally employs an oxidant to destroy a stereocenter and a reductant to reform it, as well as a chiral element to impart enantioselectivity on at least one of these steps. The highly reactive nature of oxidants and reductants towards one another has thus far precluded the development of such a deracemization by purely chemical means. We hypothesized that by separating the oxidant, substrate, and reductant into different phases, we could use a single catalyst to promote both the oxidation and subsequent enantioselective reduction of chiral substrates. This concept was used in the development of a deracemization protocol for 3H indolines and other chiral amine substrates.
