Tunable, Selective C(sp3)-h Aminations Via Silver-catalyzed Nitrene Transfer Reactions

Tunable, Selective C(sp3)-h Aminations Via Silver-catalyzed Nitrene Transfer Reactions
Author: Minxue Huang
Publisher:
Total Pages: 0
Release: 2020
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ISBN:
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Abstract The ubiquitousness of amines in pharmaceuticals, agrochemicals, ligands for transition metals, biologically active natural compounds and functional materials is the strong motivation of organic chemists to develop highly efficient yet mild reactions to install valuable C-N bonds. Transition metal-catalyzed nitrene transfer is a convenient strategy to directly functionalize a hydrocarbon substrate with amine functionality. For all means of C(sp3)−H amination, one of the core issues hampering their developments is the difficulty to differentiate multiple C-H bonds that have nearly identical electronic properties and bond strengths. As described in this work, this problem is addressed through utilizing Ag catalysts based on deliberately designed ligands, which is inspired by mechanism study, to achieve tunable site-, regio-, and stereoselectivity. Chapter 1 gives a brief introduction by providing a selected review of literature on transition metal-catalyzed C(sp3)−H aminations reactions via nitrene transfer, emphasizing the common problems associated with reactivity and selectivity. Chapter 2 demonstrates both the solid and solution-state behavior of diverse Ag(I) catalysts competent for nitrene transfor through X-ray characterization and NMR studies, and discusses our understanding of how the ligand identity manipulate those behavior of corresponding Ag(I) complexes. Chapter 3 describes both computational models and experimental probes revealing possible roles of noncovalent interactions in directing the site-selectivity of silver-catalyzed C−H aminations. Chapter 4 addresses the fluxional behavior of Ag(tpa)OTf in solution potentially hampering its site-selectivity in nitrene insertion by a rigid ligand. Finally, chapter 5 provide a novel silver catalytic system which is able to tune the selectivity between [beta] or [gamma] C-H bond amindation of an easily prepared carbamate, overriding substrate control, and amidate traditionally difficult primary aliphatic C-H bonds. Further experimental and computational studies revealed some mechanistic insights into this system. Additional, synthetic utility of this methodology was proven by the late-stage functionalization of natural products and drug-like molecules, even in gram-scale.

Enhancing Selectivity and Tunability of Nitrene Transfer Reactions Through the Coordinative Malleability of Silver Complexes

Enhancing Selectivity and Tunability of Nitrene Transfer Reactions Through the Coordinative Malleability of Silver Complexes
Author: Ryan Joseph Scamp
Publisher:
Total Pages: 0
Release: 2017
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Carbon-nitrogen bonds are common to many classes of natural products and bioactive compounds. As such, efficient methods to construct nitrogenated organic scaffolds are in constant demand. Catalytic nitrene insertions are powerful methods to introduce these functionalities to hydrocarbon groups, but they presently are limited to substrate control owing to the inherent electrophilicity of nitrene intermediates, the use of catalysts with inflexible coordination environments, and a lack of understanding as to how electronic properties of metallonitrenes influence selectivity in the reaction. Chapter 1 summarizes and explores efforts by various research groups to address these issues. Our group seeks to address this problem through the use of silver, a metal displaying an array of accessible coordination geometries, to tune for chemo-, regio-, and stereoselectivity in these reactions and thus provide opportunities to divergently functionalize complex molecules. Explorations into catalyst tunability for regioselective C-H amination reactions are detailed in Chapter 2. Immediately following, Chapter 3 will expand upon this concept and illustrate how our initial conclusions informed subsequent catalyst design. Chapter 4 describes our advances in the regioselective differentiation of adjacent methylene units and the underlying mechanistic principles governing the product distribution. Finally, Chapter 5 discusses intermolecular functionalization of alkene feedstocks and the mechanistic principles fundamental to tuning for nitrene insertion into either C=C or C-H bonds.

Development of Silver-catalyzed Chemo-, Regio- and Enantioselective Nitrene Transfer Reactions Through Rational Catalyst Design

Development of Silver-catalyzed Chemo-, Regio- and Enantioselective Nitrene Transfer Reactions Through Rational Catalyst Design
Author: Minsoo Ju
Publisher:
Total Pages: 0
Release: 2020
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ISBN:
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The development of selective C-N bond forming reactions represents an important research area because amines are prevalent in biologically active natural products, pharmaceuticals, agrochemicals, and ligands. Traditionally, the reactivity and selectivity of amine-forming reactions had a strong dependence on pre-functionalized starting materials which resulted in costly chemical steps. More direct C-H amination or C=C bond aziridination reactions via transition metal-catalyzed nitrene transfer have been brought to the synthetic community's attention recently for their potential to efficiently form valuable C-N bonds. Unfortunately, the development of efficient NT methods has been met with several challenges including substrate-dependent selectivity and the need for costly transition metal catalysts. The work described herein represents a new approach to these reactions in which rationally designed silver catalysts are utilized to achieve high chemo-, regio- and ultimately, enantioselectivity in a catalyst-controlled manner. Chapter 1 serves as an introduction by providing a selected review of literature on recent asymmetric metal-catalyzed nitrene transfer reactions emphasizing the common catalyst design strategies to solve problems associated with selectivity and reactivity. Chapter 2 describes a method for chemo- and enantioselective silver-catalyzed nitrene transfer in which homoallylic carbamates are transformed into [4.1.0]-carbamate-tethered aziridines in good yields and enantiomeric excess (ee) via intramolecular aziridination. The aziridine products undergo nucleophilic ring-opening to yield enantioenriched amines with no erosion in stereochemical integrity. Chapter 3 presents two complementary silver catalysts that are capable of selecting between [Beta] or [gamma] C(sp3)-H bonds residing in similar steric/electronic environments, overriding reaction at a weaker C-H bond in favor of a stronger one, and activating primary C-H bonds. Further experimental and computational studies revealed some mechanistic insights into this system and what seems to be causing this interesting catalyst-controlled regioselectivity. Finally, Chapter 4 offers an extension of the regioselective silver-catalyzed NT, where [gamma]-propargylic-[gamma]-amino alcohol motifs are synthesized with high site- and enantioselectivity. The protocol was enabled by a new optically active bis(oxazoline) ligand designed via a rapid structure-activity relationship analysis.

Application of Nitrene Transfer Reactions for Streamlining Amine Synthesis

Application of Nitrene Transfer Reactions for Streamlining Amine Synthesis
Author: Joshua Robert Corbin
Publisher:
Total Pages: 0
Release: 2020
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ISBN:
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Metal-catalyzed nitrene transfer is a versatile strategy for the direct incorporation of C-N bonds into organic compounds through direct C-H insertion to form amines or C=C insertion to form aziridines. The identity of the metal catalyst plays a crucial role in controlling the fate of the hyperelectrophilic nitrene when multiple reaction outcomes are possible. Part One of this thesis details the development of a catalytic system based on Ag(I) supported by diverse pyridyl N-donor ligands to achieve unprecedented and tunable site-selectivity in the amination of sterically and electronically similar tertiary C(sp3)-H bonds. When ligand-control in Ag(I) catalysis failed, exchanging the metal/ligand identity to Rh2Ln frequently provided selectivity for the orthogonal site. Further work demonstrated water could be employed as the solvent in these C-H amination reactions using Ag(I) or Rh2(II,II) catalysts and sulfamate nitrene precursors. Intramolecular chemo- and regioselective aziridination of allenes using Rh2(II,II)-catalyzed nitrene transfer provides access to bicyclic methyleneaziridine intermediates that can be rapidly diversified into complex amine-containing products by forming up to four new bonds across the cumulated pi-bonds. An underexploited strategy for accessing amidoallyl cations is treating these methyleneaziridines with a mild Lewis acid to heterolytically open the strained ring. This strategy is applied in Part Two to overcome the challenges that are associated with 3-amidopentadienyl cation imino-Nazarov electrocyclizations and the method provides access to densely functionalized aminocyclopentanes with flexible substitution patterns and control over the stereochemical outcome. This thesis in its entirety demonstrates the utility of metal-nitrenes as useful oxidants in the context of the diversity-oriented synthesis of both simple and complex amines.

Organic Reaction Mechanisms 2018

Organic Reaction Mechanisms 2018
Author: Mark G. Moloney
Publisher: John Wiley & Sons
Total Pages: 692
Release: 2021-08-17
Genre: Science
ISBN: 1119532000
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Organic Reaction Mechanisms 2018, the 54th annual volume in this highly successful and unique series, surveys research on organic reaction mechanisms described in the available literature dated 2018. The following classes of organic reaction mechanisms are comprehensively reviewed: Reaction of Aldehydes and Ketones and their Derivatives Reactions of Carboxylic, Phosphoric, and Sulfonic Acids and their Derivatives Oxidation and Reduction Carbenes and Nitrenes Nucleophilic Aromatic Substitution Electrophilic Aromatic Substitution Carbocations Nucleophilic Aliphatic Substitution Carbanions and Electrophilic Aliphatic Substitution Elimination Reactions Polar Addition Reactions Cycloaddition Reactions Molecular Rearrangements Transition Metal Coupling Radical Reactions An experienced team of authors compile these reviews every year, so that the reader can rely on a continuing quality of selection and presentation.

Expanding the Scope of Intramolecular Silver-catalyzed Nitrene Transfer

Expanding the Scope of Intramolecular Silver-catalyzed Nitrene Transfer
Author: Emily Zerull Schroeder
Publisher:
Total Pages: 0
Release: 2024
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ISBN:
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Nitrene transfer (NT) is a convenient strategy to directly transform C-H bonds into more valuable C-N bonds. Intramolecular NT reactions offer access to various N-heterocycles which are common in drugs and natural products. Many of these heterocycles can also be transformed into useful building blocks such as amino alcohols or diamines. However, the high reactivity of nitrenes often results in reactions that are primarily controlled by substrate identity, rendering these reactions less useful. This work will describe our attempts to use silver catalysts to control reactions with challenging selectivity problems such as asymmetric reactions and dearomatization reactions. Chapter 1 features a broad look at the history of transition metal catalyzed NT, followed by a more in-depth discussion of intramolecular asymmetric NT variants. Chapter 2 describes the use of silver salts ligated to an unusual, quaternary-centered bis(oxazoline) (BOX) ligand, readily accessible through a modular synthetic approach, which enables site- and enantioselective nitrene transfers into benzylic, allylic and unactivated C-H bonds of carbamate esters. The resulting 1,3-aminoalcohol building blocks are delivered in good yields and moderate-to-excellent enantioselectivities. Computational models were employed to rationalize the observed stereochemical outcomes and set the stage for the predictive design of second-generation Ag-BOX catalysts. Chapter 3 presents a combination of silver-catalysts that are able to preferentially undergo either a dearomatization event to form bicyclic azepine structures or an insertion event into the benzylic C(sp3)-H bond. This chemoselective reaction requires the use of carbamimidate precursors featuring a large sulfamate protecting group, which allows the reaction to be controlled by a combination of ligand sterics and electronics.

Iron and Cobalt Catalysts

Iron and Cobalt Catalysts
Author: Wilson D. Shafer
Publisher: MDPI
Total Pages: 414
Release: 2020-06-23
Genre: Science
ISBN: 303928388X
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Since the turn of the last century when the field of catalysis was born, iron and cobalt have been key players in numerous catalysis processes. These metals, due to their ability to activate CO and CH, haev a major economic impact worldwide. Several industrial processes and synthetic routes use these metals: biomass-to-liquids (BTL), coal-to-liquids (CTL), natural gas-to-liquids (GTL), water-gas-shift, alcohol synthesis, alcohol steam reforming, polymerization processes, cross-coupling reactions, and photocatalyst activated reactions. A vast number of materials are produced from these processes, including oil, lubricants, waxes, diesel and jet fuels, hydrogen (e.g., fuel cell applications), gasoline, rubbers, plastics, alcohols, pharmaceuticals, agrochemicals, feed-stock chemicals, and other alternative materials. However, given the true complexities of the variables involved in these processes, many key mechanistic issues are still not fully defined or understood. This Special Issue of Catalysis will be a collaborative effort to combine current catalysis research on these metals from experimental and theoretical perspectives on both heterogeneous and homogeneous catalysts. We welcome contributions from the catalysis community on catalyst characterization, kinetics, reaction mechanism, reactor development, theoretical modeling, and surface science.

Alkane C-H Activation by Single-Site Metal Catalysis

Alkane C-H Activation by Single-Site Metal Catalysis
Author: Pedro J. Pérez
Publisher: Springer Science & Business Media
Total Pages: 277
Release: 2012-09-15
Genre: Science
ISBN: 9048136989
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Over the past decade, much research effort has been devoted to the design and synthesis of new reagents and catalysts that can influence carbon-hydrogen bond activation, mainly because of the prospect that C−H activation could enable the conversion of cheap and abundant alkanes into valuable functionalized organic compounds. Alkane C-H Activation by Single-Site Metal Catalysis presents the current state-of-the-art development in the catalytic systems for the catalytic trans-formations of alkanes under homogeneous conditions. Chapter 1 offers a comprehensive summary of the main discoveries realized so far. Chapter 2 reviews the so-called electrophilic activation, initiated by Shulpín in the late 60s, and the base for the Catalytica system. Chapter 3 examines the catalytic borylation of alkanes, discovered by Hartwig, whereas chapter 4 provides an updated vision of the alkane dehydrogenation reaction. Chapter 5 covers the oxygenation of C-H bonds, a field of enormous interest with bioinorganic im-plications, and finally chapter 6 presents the functionalization of alkane C-H bonds by carbene or nitrene insertion. The history of C-H bond activation, and the current research described in this book, highlight the current research and present the reader with an outlook of this field which continues to be explored by an increasingly visionary and enthusiastic group of organic, organometallic, biological and physical chemists.

C-H Bond Activation and Catalytic Functionalization II

C-H Bond Activation and Catalytic Functionalization II
Author: Pierre H. Dixneuf
Publisher: Springer
Total Pages: 213
Release: 2016-03-10
Genre: Science
ISBN: 3319293192
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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.