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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.
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.
Author: A. Stephen K. Hashmi
Publisher: John Wiley & Sons
ISBN: 3527319522
Category : Science
Languages : en
Pages : 419
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Book Description
With its impressive features, gold has led to completely new reaction types in recent years, which in turn have strongly influenced both organic catalysis and material science. Other fields where a significant amount of new results has been obtained include nanotechnology, self assembly/supramolecular systems and biochemical/medicinal chemistry. As a result, gold is one of the hottest topics in catalysis at the moment, with an increasing amount of research being carried out in this field. While focusing on homogeneous catalysis, this monograph also covers the main applications in heterogeneous catalysis. Following a look at the gold-catalyzed addition of heteroatom nucleophiles to alkynes, it goes on to discuss gold-catalyzed additions to allenes and alkenes, gold-catalyzed benzannulations, cycloisomerization and rearrangement reactions, as well as oxidation and reduction reactions. The whole is finished off with a section on gold-catalyzed aldol and related reactions and the application of gold-catalyzed reactions to natural product synthesis. Of interest to synthetic chemists and inorganic chemists, as well as organic chemists working in homogeneous catalysis, physical and technical chemists.
Author: Veronique Michelet
Publisher: World Scientific
ISBN: 1783265558
Category : Science
Languages : en
Pages : 564
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Book Description
Research on designing new catalytic systems has been one of the most important fields in modern organic chemistry. One reason for this is the predominant contribution of catalysis to the concepts of atom economy and green chemistry in the 21st century. Gold, considered catalytically inactive for a long time, is now a fascinating partner of modern chemistry, as scientists such as Bond, Teles, Haruta, Hutchings, Ito and Hayashi opened new perspectives for the whole synthetic chemist community. This book presents the major advances in homogeneous catalysis, emphasizing the methodologies that create carbon-carbon and carbon-heteroatom bonds, the applications that create diversity and synthesize natural products, and the recent advances and challenges in asymmetric catalysis and computational research.It provides readers with in-depth information about homogeneous gold-catalyzed reactions and presents several explanations for the scientific design of a catalyst. Readers will be able to understand the entire gold area and find solutions to problems in catalysis.Gold Catalysis — An Homogeneous Approach is part of the Catalytic Science Series and features prominent authors who are experts in their respective fields.
Author: Laura Prati
Publisher: CRC Press
ISBN: 9814669296
Category : Science
Languages : en
Pages : 521
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Book Description
Since the first report on alcohol oxidation in 1998, many studies have highlighted some peculiarity of gold with respect to other metals. Some analogies have been found between gas and liquid phases, but the big challenge to operate in a condensed phase lies in the role of the solvent in tuning the reactant-catalyst contact. Liquid-phase oxidation
Author: Rebecca Lyn K. C. LaLonde
Publisher:
ISBN:
Category :
Languages : en
Pages : 672
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Book Description
The addition of nitrogen, oxygen, and carbon nucleophiles to carbon-carbon unsaturated bonds is an atom economical method of generating structural complexity from simple starting materials. As soft Lewis acids with high oxidation potentials, gold(I)-complexes are attractive catalysts for these types of transformations. Although many reactions catalyzed by gold(I) have now been reported, we identified two conspicuous deficiencies: few of enantioselective methods and a lack of nucleophilic additions to alkenes. This dissertation will describe advances on both fronts. First, we will discuss the discovery and characterization of chiral phosphinegold(I)-bis-p-nitrobenzoate complexes which catalyze the asymmetric hydroamination of allenes. Second, the isolation of proposed alkene hydroamination intermediates will be reported. Chapter 1. A brief perspective on the current resurgence of homogeneous gold(I)-catalysis will be presented, with an emphasis on the development of enantioselective reactions. Chapter 2. The metal catalyzed asymmetric hydroamination of allenes has been an unsolved problem in syntheic chemistry for many years. In this chapter, we describe our efforts to apply chiral biarylposphinegold(I) complexes to this transformation. Over the course of this work, we characterized a polymeric mono-cationic complex (R)-[BINAP(Au2Cl)]BF4, and uncovered a dramatic counterion effect. This discovery led to the utilization of phosphinegold(I)-bis-p-nitrobenzoate complexes for the asymmetric hydroamination of allenes. The catalysts were applied to the enantioselective formation of vinyl pyrrolidines and piperidines in 70-99% enantiomeric excess. The structure of a bis-p-nitrobenzoategold(I) complex, (R)-ClMeOBiPHEP(AuOPNB)2, was verified by X-ray crystallography. Chapter 3. Chiral ligands and counterions were employed in the gold(I)-catalyzed enantioselective intramolecular additions of hydrazines and hydroxylamines to allenes. Chiral phosphinegold(I)-bis-p-nitrobenzoate complexes are versatile catalysts for the enantioselective hydroamination of allenes. The addition of oxygen nucleophiles, however, required the use of chiral anions. These complementary methods allow access to chiral vinyl isoxolidines, tetrahydrooxazines, and differentially protected pyrazolidines. Chapter 4. This chapter will describe the first direct experimental evidence for the elementary step of gold-promoted nucleophilic addition to an alkene. Alkylgold(I) complexes were formed from the gold(I)-promoted intramolecular addition of various amine nucleophiles to alkenes. Deuterium-labeling studies and X-ray crystal structures provided support for a mechanism involving anti-addition of the nucleophile to a gold-activated alkene. This mechanism was verified by DFT analysis. Ligand studies indicated that the rate of aminoauration was drastically increased by use of electron-poor arylphosphines, which were also shown to be favored in ligand exchange experiments. Attempts at protodeauration led only to recovery of the starting olefins, though the gold could be removed under reducing conditions to provide the purported hydroamination products. The reactivity of alkylgold complexes with zinc and palladium are described. An unexpected oxidation to gold(III) was also uncovered. Chapter 5. Investigations into the gold(I)-catalyzed addition of carbon nucleophiles to allenes will be discussed. One such reaction, a gold(I)-catalyzed 5-endo-trig reaction, worked with a variety of carbon nucleophiles, incuding silyl enol ethers, [beta]-ketoesters and dinitriles. This transformation opens access to a variety of substituted cyclopentenes. These carbocycles are complementary to the products available through the Conia-ene and 5-endo-dig methodology. In addition, we demonstrate the transfer of chirality from an allene precursor, producing a quaternary stereocenter with a vicinal tertiary center. We also report a gold(I)-catalyzed 5-endo/exo-trig cyclization of substrates which contain two-carbon linkers between the pendant nucleophile and allene. Investigations into the mechanism of this cyclization are included, as well as attempts to isolate a proposed allylgold(I) intermediate. Chapter 6. A synopsis of our results will be presented, with a perspective on the evolving field of gold(I)-catalysis.
Author: Geoffrey C Bond
Publisher: World Scientific
ISBN: 1908979852
Category : Science
Languages : en
Pages : 383
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Book Description
Gold has traditionally been regarded as inactive as a catalytic metal. However, the advent of nanoparticulate gold on high surface area oxide supports has demonstrated its high catalytic activity in many chemical reactions. Gold is active as a heterogeneous catalyst in both gas and liquid phases, and complexes catalyse reactions homogeneously in solution. Many of the reactions being studied will lead to new application areas for catalysis by gold in pollution control, chemical processing, sensors and fuel cell technology. This book describes the properties of gold, the methods for preparing gold catalysts and ways to characterise and use them effectively in reactions. The reaction mechanisms and reasons for the high activities are discussed and the applications for gold catalysis considered./a
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:
Publisher:
ISBN:
Category :
Languages : en
Pages : 233
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Book Description
Chapter 1 A mild, versatile, and convenient method for the efficient oxytrifluoromethylation of unactivated alkenes based on a copper-catalyzed ligand-assisted difunctionalization strategy has been developed. This method provides access to a variety of classes of synthetically useful CF3-containing building blocks from simple starting materials. Chapter 2 A method for the efficient enantioselective oxytrifluoromethylation of alkenes has been developed using a copper catalyst system inspired by the ligand dependence observed in the racemic reaction. Mechanistic studies are consistent with a metal-catalyzed redox radical addition mechanism, in which a C-0 bond is formed via the copper-mediated enantioselective trapping of a prochiral alkyl radical intermediate derived from the initial trifluoromethyl radical addition. Chapter 3 A general and versatile method for the catalytic enantioselective oxyfunctionalization of alkenes has been developed based on a key Cu-mediated enantioselective C-0 bond forming process of prochiral alkyl radical intermediates. A wide range of radicals were found to participate this type of reaction, including azidyl, arylsulfonyl, aryl, acyloxyl and alkyl radicals. This method provides rapid access to a broad spectrum of interesting enantiomerically enriched lactones through tandem C-N/C-O, C-S/C-O, C-Cary/aIkyI/C-O or C-O/C-O bond formation, in good yields and enantiomeric excesses with good functional group compatibility.
Author: Andy Wei Jen Yen
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The synthesis of heterocycles using transition metal catalysis is a topic of broad interest in the field of organic chemistry. Transition metal catalysts allow many diverse bond disconnections to be realized, allowing for many ways to assemble heterocycles. Many of the transformations developed in the Lautens group are aimed at atom economical bond construction processes that streamline synthesis and minimize waste. The arylcyanation reaction and the asymmetric ring opening (ARO) reaction are two examples of methods developed in our group that embody this design principle. Chapter 1 of this thesis describes the development of a nickel-catalyzed arylcyanation reaction for the synthesis of 3,3-disubstituted oxindoles. This method was inspired by our work on the palladium-catalyzed arylcyanation reaction, originally developed to address challenges in the formal synthesis of (+)-corynoline. This nickel-catalyzed reaction uses an air-stable catalyst precursor to achieve a highly practical synthesis of a nitrile-containing oxindole via a domino Heck-cyanide capture cascade. Derivatizations of the nitrile group affords a series of novel heterocyclic scaffolds. Chapter 2 details the discovery and development of a novel enantioselective cycloisomerization reaction of oxabicyclic alkenes. Our work on developing the intramolecular asymmetric ring opening reaction led to the discovery of a novel epoxide synthesis. Specifically, when bridgehead substituted oxabicyclic alkenes with non-nucleophilic side chains are reacted with the [Rh(cod)2]OTf/PPF-PtBu2 catalyst in the absence of an external nucleophile, chiral epoxides are obtained. The synthesis of epoxides through cycloisomerization reactions possesses 100% atom economy and avoids the use of external oxidant. Chapter 3 describes an asymmetric ring opening reaction, specifically to address gaps in the methodology concerning amine nucleophiles. We were inspired by our group's previous attempts to use amino acid derived nucleophiles in the ARO reaction. We developed a way to incorporate amino acids into the ARO reaction by employing their 2-nitrobenzenesulfonamide (nosyl) derivatives as pronucleophiles. Intriguingly, we observed a divergence in reactivity between the diastereomeric hydroxyester products, in that one diastereomer was capable of lactonization and the other was not. This led to the enantioselective synthesis of chiral oxazinones, which are similar to the naphthoxazine class of compounds which possess dopaminergic activity.
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.
