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Palladium Catalyzed Reductive Cross Coupling Reactions And The Analysis Of Site Selectvity In Rhodium Catalyzed C H Amination Reactions
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Book Synopsis Palladium-catalyzed Reductive Cross-coupling Reactions and the Analysis of Site-selectvity in Rhodium-catalyzed C-H Amination Reactions by : Ryan James DeLuca
Download or read book Palladium-catalyzed Reductive Cross-coupling Reactions and the Analysis of Site-selectvity in Rhodium-catalyzed C-H Amination Reactions written by Ryan James DeLuca and published by . This book was released on 2014 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Oxidative Cross-Coupling Reactions by : Aiwen Lei
Download or read book Oxidative Cross-Coupling Reactions written by Aiwen Lei and published by John Wiley & Sons. This book was released on 2016-11-14 with total page 243 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first handbook on this emerging field provides a comprehensive overview of transition metal-catalyzed coupling reactions in the presence of an oxidant. Following an introduction to the general concept and mechanism of this reaction class, the team of authors presents chapters on C-C cross-coupling reactions using organometallic partners, C-Heteroatom bond forming reactions via oxidative couplings, and C-H couplings via C-H activation. The text also covers such groundbreaking topics as recent achievements in the fields of C-C and C-X bond formation reactions as well as C-H activation involving oxidative couplings. With its novel and concise approach towards important building blocks in organic chemistry and its focus on synthetic applications, this handbook is of great interest to all synthetic chemists in academia and industry alike.
Book Synopsis Rhodium Catalysis in Organic Synthesis by : Ken Tanaka
Download or read book Rhodium Catalysis in Organic Synthesis written by Ken Tanaka and published by John Wiley & Sons. This book was released on 2019-05-06 with total page 684 pages. Available in PDF, EPUB and Kindle. Book excerpt: An essential reference to the highly effective reactions applied to modern organic synthesis Rhodium complexes are one of the most important transition metals for organic synthesis due to their ability to catalyze a variety of useful transformations. Rhodium Catalysis in Organic Synthesis explores the most recent progress and new developments in the field of catalytic cyclization reactions using rhodium(I) complexes and catalytic carbon-hydrogen bond activation reactions using rhodium(II) and rhodium(III) complexes. Edited by a noted expert in the field with contributions from a panel of leading international scientists, Rhodium Catalysis in Organic Synthesis presents the essential information in one comprehensive volume. Designed to be an accessible resource, the book is arranged by different reaction types. All the chapters provide insight into each transformation and include information on the history, selectivity, scope, mechanism, and application. In addition, the chapters offer a summary and outlook of each transformation. This important resource: -Offers a comprehensive review of how rhodium complexes catalyze a variety of highly useful reactions for organic synthesis (e.g. coupling reactions, CH-bond functionalization, hydroformylation, cyclization reactions and others) -Includes information on the most recent developments that contain a range of new, efficient, elegant, reliable and useful reactions -Presents a volume edited by one of the international leading scientists working in the field today -Contains the information that can be applied by researchers in academia and also professionals in pharmaceutical, agrochemical and fine chemical companies Written for academics and synthetic chemists working with organometallics, Rhodium Catalysis in Organic Synthesis contains the most recent information available on the developments and applications in the field of catalytic cyclization reactions using rhodium complexes.
Book Synopsis Palladium-Catalyzed Mechanochemical Cross-Coupling Reactions by : Tamae Seo
Download or read book Palladium-Catalyzed Mechanochemical Cross-Coupling Reactions written by Tamae Seo and published by Springer Nature. This book was released on with total page 287 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Palladium-Catalyzed Coupling Reactions by : Árpád Molnár
Download or read book Palladium-Catalyzed Coupling Reactions written by Árpád Molnár and published by John Wiley & Sons. This book was released on 2013-02-14 with total page 531 pages. Available in PDF, EPUB and Kindle. Book excerpt: This handbook and ready reference brings together all significant issues of practical importance in selected topics discussing recent significant achievements for interested readers in one single volume. While covering homogeneous and heterogeneous catalysis, the text is unique in focusing on such important aspects as using different reaction media, microwave techniques or catalyst recycling. It also provides a comprehensive treatment of key issues of modern-day coupling reactions having emerged and matured in recent years and emphasizes those topics that show potential for future development, such as continuous flow systems, water as a reaction medium, and catalyst immobilization, among others. With its inclusion of large-scale applications in the pharmaceutical industry, this will equally be of great interest to industrial chemists. From the contents * Palladium-Catalyzed Cross-Coupling Reactions - A General Introduction * High-turnover Heterogeneous Palladium Catalysts in Coupling Reactions: the Case of Pd Loaded on Dealuminated Y Zeolites Palladium-Catalyzed Coupling Reactions with Magnetically Separable Nanocatalysts * The Use of Ordered Porous Solids as Support Materials in Palladium-Catalyzed Cross-Coupling Reactions * Coupling Reactions Induced by Polymer-Supported Catalysts * Coupling Reactions in Ionic Liquids * Cross-Coupling Reactions in Aqueous Media * Microwave-Assisted Synthesis in C-C and C-Heteroatom Coupling Reactions * Catalyst Recycling in Palladium-Catalyzed Carbon-Carbon Coupling Reactions * Nature of the True Catalytic Species in Carbon-Carbon Coupling Reactions with * Heterogeneous Palladium Precatalysts * Coupling Reactions in Continuous Flow Systems * Large-Scale Applications of Palladium-Catalyzed Couplings in the Pharmaceutical Industry
Book Synopsis Modern Rhodium-Catalyzed Organic Reactions by : P. Andrew Evans
Download or read book Modern Rhodium-Catalyzed Organic Reactions written by P. Andrew Evans and published by John Wiley & Sons. This book was released on 2006-03-06 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rhodium has proven to be an extremely useful metal due to its ability to catalyze an array of synthetic transformations, with quite often-unique selectivity. Hydrogenation, C-H activation, allylic substitution, and numerous other reactions are catalyzed by this metal, which presumably accounts for the dramatic increase in the number of articles that have recently emerged on the topic. P. Andrew Evans, the editor of this much-needed book, has assembled an internationally renowned team to present the first comprehensive coverage of this important area. The book features contributions from leaders in the field of rhodium-catalyzed reactions, and thereby provides a detailed account of the most current developments, including: Rhodium-Catalyzed Asymmetric Hydrogenation (Zhang) Rhodium-Catalyzed Hydroborations and Related Reactions (Brown) Rhodium-Catalyzed Asymmetric Addition of Organometallic Reagents to Electron Deficient Olefins (Hayashi) Recent Advances in Rhodium(I)-Catalyzed Asymmetric Olefin Isomerization and Hydroacylation Reactions (Fu) Stereoselective Rhodium(I)-Catalyzed Hydroformylation and Silylformylation Reactions and Their Application to Organic Synthesis (Leighton) Carbon-Carbon Bond-Forming Reactions Starting from Rh-H or Rh-Si Species (Matsuda) Rhodium(I)-Catalyzed Cycloisomerization and Cyclotrimerization Reactions (Ojima) The Rhodium(I)-Catalyzed Alder-ene Reaction (Brummond) Rhodium-Catalyzed Nucleophilic Ring Cleaving Reactions of Allylic Ethers and Amines (Fagnou) Rhodium(I)-Catalyzed Allylic Substitution Reactions and their Applications to Target Directed Synthesis (Evans) Rhodium(I)-Catalyzed [2+2+1] and [4+1] Carbocyclization Reactions (Jeong) Rhodium(I)-Catalyzed [4+2] and [4+2+2] Carbocyclizations (Robinson) Rhodium(I)-Catalyzed [5+2], [6+2], and [5+2+1] Cycloadditions: New Reactions for Organic Synthesis (Wender) Rhodium(II)-Stabilized Carbenoids Containing both Donor and Acceptor Substituents (Davies) Chiral Dirhodium(II)Carboxamidates for Asymmetric Cyclopropanation and Carbon-Hydrogen Insertion Reactions (Doyle) Cyclopentane Construction by Rhodium(II)-Mediated Intramolecular C-H Insertion (Taber) Rhodium(II)-Catalyzed Oxidative Amination (DuBois) Rearrangement Processes of Oxonium and Ammonium Ylides Formed by Rhodium(II)-Catalyzed Carbene-Transfer (West) Rhodium(II)-Catalyzed 1,3-Dipolar Cycloaddition Reactions (Austin) "Modern Rhodium-Catalyzed Organic Reactions" is an essential reference text for researchers at all levels in the general area of organic chemistry. This book provides an invaluable overview of the most significant developments in this important area of research, and will no doubt be an essential text for researchers at academic institutions and professionals at pharmaceutical/agrochemical companies.
Book Synopsis Rhodium-Catalyzed Asymmetric Ring Opening of Oxabicyclic Alkenes and Palladium-Catalyzed Carbon-Halogen Bond Forming Reactions by : Christine Le
Download or read book Rhodium-Catalyzed Asymmetric Ring Opening of Oxabicyclic Alkenes and Palladium-Catalyzed Carbon-Halogen Bond Forming Reactions written by Christine Le and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atom-economical addition reactions to unsaturated carbonâ carbon bonds represent a powerful class of transformations in organic chemistry, since a great deal of molecular complexity can be generated from simple starting materials. Highly regio- and stereoselective processes have been made possible through the use of transition metal catalysts, alongside specialized ancillary ligands and in combination with rational substrate design. One area of research in the Lautens group involves the transition metal catalyzed asymmetric ring opening (ARO) of strained alkenes, which provides access to enantioenriched carbocyclic frameworks. Although a variety of coupling partners have been applied in this transformation, the use of soft carbon nucleophiles remains limited in scope. The first chapter describes a rhodium(I)-catalyzed ARO of meso-oxabicyclic alkenes using silyl enol ethers and ketene acetals. In analogy to the Mukaiyama aldol reaction, a novel silyl migration occurs, enabling an in situ protection of the chiral alcohols obtained. Developing new reactivity from Heck-type carbopalladation processes represents another research interest in the Lautens group. Oxidative addition into a carbonâ halogen bond constitutes the first step of nearly all palladium(0)-catalyzed cross-couplings. Conversely, reductive elimination from palladium(II) to yield an organohalide product represents a rare and often thermodynamically unfavoured process. The next two chapters address challenges in the synthesis of vinyl halides using palladium(0) catalysis via the intramolecular carbohalogenation and chlorocarbamoylation of alkynes. During our investigations, we discovered that the steric bulk of both the substrate and the phosphine ligand play an important role in promoting the desired reactivity. Mechanistic insight has been gained through combined experimental and computational studies, which implicate a palladium-catalyzed stereoisomerization in both of these transformations. Under certain conditions, we demonstrate that highly stereoselective trans-additions to alkynes can be achieved, which illustrates that specific substrate/catalyst combinations can override the inherent cis-selectivity in carbometallations. In the fourth chapter, a formal palladium(II)-catalyzed alkyne chlorocarbamoylation reaction is presented, which provides access to medicinally relevant methylene oxindole scaffolds. In contrast to the analogous protocol using palladium(0) catalysts, the reaction is initiated by an alkyne chloropalladation step, followed by intramolecular cross-coupling with a carbamoyl chloride. Experimental and computational studies provide insight into the mechanism of this reaction.
Book Synopsis Metal Catalyzed Cross-Coupling Reactions and More by : Armin de Meijere
Download or read book Metal Catalyzed Cross-Coupling Reactions and More written by Armin de Meijere and published by John Wiley & Sons. This book was released on 2013-12-04 with total page 1640 pages. Available in PDF, EPUB and Kindle. Book excerpt: This three volume book is the follow-up handbook to the bestselling volume "Metal-Catalyzed Cross-Coupling Reactions", the definitive reference in the field. In line with the enormous developments in this area, this is not a new edition, but rather a new book in three volumes with over 50% more content. This new content includes C-H activation, shifting the focus away from typical cross-coupling reactions, while those topics and chapters found in de Meijere/Diederich's book have been updated and expanded. With its highly experienced editor team and the list of authors reading like an international Who's-Who in the field, this work will be of great interest to every synthetic chemist working in academia and industry.
Book Synopsis New Reactivity and Selectivity in Transition Metal-catalyzed C-C and C-N Bond Forming Processes by :
Download or read book New Reactivity and Selectivity in Transition Metal-catalyzed C-C and C-N Bond Forming Processes written by and published by . This book was released on 2015 with total page 881 pages. Available in PDF, EPUB and Kindle. Book excerpt: Part I. Palladium-Catalyzed Carbon-Carbon Bond Forming Cross-Couplings Chapter 1. Ligand-Controlled Palladium-Catalyzed Regiodivergent Suzuki-Miyaura Cross-Coupling of Allylboronates and Aryl Halides An orthogonal set of catalyst systems based on the use of two biarylphosphine ligands has been developed for the Suzuki-Miyaura coupling of 3,3-disubstituted and 3-monosubstituted allylboronates with (hetero)aryl halides. These methods allow for the regiodivergent preparation of either the ct- or the [gamma]-isomeric coupling product with high levels of site selectivity using a common allylboron building block. Preliminary investigations have demonstrated the feasibility of an enantioselective variant for the [gamma]-selective cross-coupling using chiral monodentate biarylphosphine ligands. Chapter 2. Palladium-Catalyzed Completely Linear-Selective Negishi Coupling of 3,3-Disubstituted Organozinc Reagents with Aryl and Vinyl Electrophiles A palladium-catalyzed general and completely linear-selective Negishi coupling of 3,3- disubstituted allyl organozinc reagents with (hetero)aryl and vinyl electrophiles has been developed. This method provided an effective means for accessing highly functionalized aromatic and heteroaromatic compounds bearing prenyl-type side chains. The utility of the current protocol was further illustrated in the concise synthesis of the anti-HIV natural product siamenol. Chapter 3. Palladium-Catalyzed Highly Selective Negishi Cross-Coupling of Secondary Alkylzinc Reagents with Aryl and Heteroaryl Halides The palladium-catalyzed Negishi cross-coupling of secondary alkylzinc reagents and heteroaryl halides with high levels of regioisomeric retention has been described. The development of a series of biarylphosphine ligands has led to the identification of an improved catalyst for the coupling of electron-deficient heterocyclic substrates. Preparation and characterization of oxidative addition complex (L)Pd(Ar)(Br) provided insight into the unique reactivity of palladium catalysts based on CPhos-type biarylphosphine ligands in facilitating challenging reductive elimination processes. Chapter 4. Mechanistic Studies on the Aryl-Trifluoromethyl Reductive Elimination from Pd(II) Complexes Based on Biarylphosphine Ligands A series of monoligated (L)Pd(Ar)(CF3) (L = dialkyl biarylphosphine) have been prepared and studied in an effort to shed light on the mechanism of the aryl-trifluoromethyl reductive elimination from these systems. Combined experimental and computational investigations revealed unique reactivity and binding modes of (L)Pd(Ar)(CF3) complexes derived from BrettPhos-type biarylphosphines. In contrast to a variety of C-C and C-heteroatom bond forming reductive eliminations, kinetic measurements showed this Ar-CF3 reductive elimination is largely insensitive to the electronic nature of the to-be-eliminated aryl substituent. Furthermore, the aryl group serves as the nucleophilic coupling partner in this reductive elimination process. The structure-reactivity relationship of biarylphosphine ligands was also investigated, uncovering distinct roles of the ipso-arene and alkoxy interactions in affecting these reductive elimination reactions. Part II. Copper-Catalyzed Carbon-Carbon and Carbon-Nitrogen Bond Formation via Olefin Functionalization Chapter 5. Copper-Catalyzed ortho C-H Cyanation of Vinylarenes A copper-catalyzed regioselective ortho C-H cyanation of vinylarenes has been developed. This method provides an effective means for the selective functionalization of vinylarene derivatives. A copper-catalyzed cyanative dearomatization mechanism is proposed to account for the regiochemical course of this reaction. This mechanism has been validated through density functional theory calculations. Computational studies revealed that the high level of ortho selectivity in the electrophilic cyanation event originates from a unique six-membered transition state that minimizes unfavorable steric repulsions. Chapter 6. Regio- and Stereospecific 1,3-Allyl Group Transfer Triggered by a Copper-Catalyzed Borylation/ortho-Cyanation Cascade A copper-catalyzed borylation/cyanation/allyl group transfer cascade has been developed. This process features an unconventional copper-catalyzed electrophilic dearomatization followed by the subsequent regio- and stereospecific 1,3-transposition of the allyl fragment enabled by the aromatization-driven Cope rearrangement. This method provides an effective means for the construction of adjacent tertiary and quaternary stereocenters with high levels of stereochemical purity. Chapter 7. Copper-Catalyzed Asymmetric Hydroamination of Unactivated Internal Olefins: an Effective Means to Access Highly Enantioenriched Aliphatic Amines Catalytic assembly of enantiopure aliphatic amines from abundant and readily available precursors has long been recognized as a paramount challenge in synthetic chemistry. We describe a mild and general copper-catalyzed hydroamination that effectively converts unactivated internal olefins-an important yet unexploited class of abundant feedstock chemicals-into highly enantioenriched [alpha]-branched amines (>/= 96% ee) featuring two minimally differentiated aliphatic substituents. This method provides a powerful means to access a broad range of advanced, highly functionalized enantioenriched amines of interest in pharmaceutical research and other areas.
Book Synopsis The Development and Application of Rhodium-catalyzed C-H Amination Reactions in the Synthesis of Bromopyrrole Alkaloids by : Paul Manning Wehn
Download or read book The Development and Application of Rhodium-catalyzed C-H Amination Reactions in the Synthesis of Bromopyrrole Alkaloids written by Paul Manning Wehn and published by . This book was released on 2005 with total page 1074 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Cross-Coupling Reactions by : Norio Miyaura
Download or read book Cross-Coupling Reactions written by Norio Miyaura and published by Springer. This book was released on 2003-07-01 with total page 253 pages. Available in PDF, EPUB and Kindle. Book excerpt: In 1972, a very powerful catalytic cycle for carbon-carbon bond formation was 2 first discovered by the coupling reaction of Grignard reagents at the sp -carbon. Over the past 30 years, the protocol has been substantially improved and expanded to other coupling reactions of Li,B,N,O,Al,Si,P,S,Cu,Mn,Zn,In,Sn, and Hg compounds. These reactions provided an indispensable and simple methodology for preparative organic chemists. Due to the simplicity and rel- bility in the carbon-carbon, carbon-heteroatom, and carbon-metalloid bo- formations,as well as high efficiency of the catalytic process,the reactions have been widely employed by organic chemists in various fields. Application of the protocol ranges from various syntheses of complex natural products to the preparation of biologically relevant molecules including drugs, and of sup- molecules, and to functional materials. The reactions on solid surfaces allow robot synthesis and combinatorial synthesis. Now, many organic chemists do not hesitate to use transition metal complexes for the transformation of org- ic molecules. Indeed, innumerable organic syntheses have been realized by the catalyzed reactions of transition metal complexes that are not achievable by t- ditional synthetic methods. Among these, the metal-catalyzed cross-coupling reactions have undoubtedly contributed greatly to the development of such a new area of “metal-catalyzed organic syntheses”. An excellent monograph for the cross-coupling reactions and other met- catalyzed C-C bond-forming reactions recently appeared in Metal-catalyzed Cross-coupling Reactions (Wiley-VCH,1998).
Book Synopsis Artificial Metalloenzymes and MetalloDNAzymes in Catalysis by : Montserrat Diéguez
Download or read book Artificial Metalloenzymes and MetalloDNAzymes in Catalysis written by Montserrat Diéguez and published by John Wiley & Sons. This book was released on 2018-02-21 with total page 431 pages. Available in PDF, EPUB and Kindle. Book excerpt: An important reference for researchers in the field of metal-enzyme hybrid catalysis Artificial Metalloenzymes and MetalloDNAzymes in Catalysis offers a comprehensive review of the most current strategies, developed over recent decades, for the design, synthesis, and optimization of these hybrid catalysts as well as material about their application. The contributors—noted experts in the field—present information on the preparation, characterization, and optimization of artificial metalloenzymes in a timely and authoritative manner. The authors present a thorough examination of this interesting new platform for catalysis that combines the excellent selective recognition/binding properties of enzymes with transition metal catalysts. The text includes information on the various applications of metal-enzyme hybrid catalysts for novel reactions, offers insights into the latest advances in the field, and contains an informative perspective on the future: Explores the development of artificial metalloenzymes, the modern and strongly evolving research field on the verge of industrial application Contains a comprehensive reference to the research area of metal-enzyme hybrid catalysis that has experienced tremendous growth in recent years Includes contributions from leading researchers in the field Shows how this new catalysis combines the selective recognition/binding properties of enzymes with transition metal catalysts Written for catalytic chemists, bioinorganic chemists, biochemists, and organic chemists, Artificial Metalloenzymes and MetalloDNAzymes in Catalysis offers a unique reference to the fundamentals, concepts, applications, and the most recent developments for more efficient and sustainable synthesis.
Book Synopsis Handbook of Organopalladium Chemistry for Organic Synthesis by : Ei-ichi Negishi
Download or read book Handbook of Organopalladium Chemistry for Organic Synthesis written by Ei-ichi Negishi and published by John Wiley & Sons. This book was released on 2003-11-24 with total page 1697 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organized to provide maximum utility to the bench synthetic chemist. The editor is well-known for his work in exploring, developing, and applying organopalladium chemistry. Contributors include over 24 world authorities in the field.
Book Synopsis A Theoretical Study of Pd-Catalyzed C-C Cross-Coupling Reactions by : Max García Melchor
Download or read book A Theoretical Study of Pd-Catalyzed C-C Cross-Coupling Reactions written by Max García Melchor and published by Springer. This book was released on 2016-08-23 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Find out how theoretical calculations are used to determine, elucidate and propose mechanisms for Pd-catalyzed C-C cross-coupling reactions in Max Garcia Melchor's outstanding thesis. Garcia Melchor investigates one of the most significant and useful types of reactions in modern organic synthesis; the Pd-cross coupling reaction. Due to its versatility, broad scope and selectivity under mild conditions, this type of reaction can now be applied in fields as diverse as the agrochemical and pharmaceutical industry. Garcia Melchor studies the reaction intermediates and transition states involved in the Negishi, the copper-free Sonogashira and the asymmetric version of Suzuki-Miyaura coupling. He also characterizes and provides a detailed picture of the associated reaction mechanisms. The author has won numerous prizes for this work which has led to over eight publications in internationally renowned journals.
Book Synopsis Palladium- and Nickel-catalyzed C-N Cross-coupling Reactions Featuring Soluble Organic Bases by : Joseph Michael Dennis (Jr.)
Download or read book Palladium- and Nickel-catalyzed C-N Cross-coupling Reactions Featuring Soluble Organic Bases written by Joseph Michael Dennis (Jr.) and published by . This book was released on 2020 with total page 549 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1: Breaking the Base Barrier: An Electron-Deficient Palladium Catalyst Enables the Use of a Common Soluble Base in C-N Coupling Due to the low intrinsic acidity of amines, palladium-catalyzed C-N cross-coupling plagued continuously by the necessity to employ strong, inorganic, or insoluble bases. To surmount the many Due to the low intrinsic acidity of amines, palladium-catalyzed C-N crosscoupling has been practical obstacles associated with these reagents, we utilized a commercially available dialkyl triarylmonophosphine-supported palladium catalyst that facilitates a broad range of C-N coupling reactions in the presence of weak, soluble bases. The mild and general reaction conditions show extraordinary tolerance for even highly base-sensitive functional groups. Additionally, insightful heteronuclear NMR studies using −15N-labeled amine complexes provide evidence for the key acidifying effect of the cationic palladium center. Chapter 2: Pd-Catalyzed C-N Coupling Reactions Facilitated by Organic Bases: Mechanistic Investigation Leads to Enhanced Reactivity in the Arylation of Weakly Binding Amines The ability to use soluble organic amine bases in Pd-catalyzed C-N cross-coupling reactions has provided a long-awaited solution to the many issues associated with employing traditional, heterogeneous reaction conditions. However, little is known about the precise function of these bases in the catalytic cycle or about the effect of variations in base structure on catalyst reactivity. We used 19F NMR to analyze the kinetic behavior of C-N coupling reactions facilitated by different organic bases. In the case of aniline coupling reactions employing DBU, the resting state was a DBU-bound oxidative addition complex, LPd(DBU)(Ar)X, and the reaction was found to be inhibited by base. Generally, however, depending on the binding properties of the chosen organic base, increasing the concentration of the base can have a positive or negative influence on the reaction rate. Furthermore, the electronic nature of the aryl triflate employed in the reaction directly affects the reaction rate. The fastest reaction rates were observed with electronically neutral aryl triflates, while the slowest were observed with highly electron-rich and electrondeficient substrates. We propose a model in which the turnover-limiting step of the catalytic cycle is dependent on the relative nucleophilicity of the base, compared to that of the amine. This hypothesis guided the discovery of new reaction conditions for the coupling of weakly binding amines, including secondary aryl amines, which were unreactive nucleophiles in our original protocol. Chapter 3: Use of a Droplet Platform to Optimize Pd-Catalyzed C-N Coupling Reactions Promoted by Organic Bases Recent advances in Pd-catalyzed carbon-nitrogen cross-coupling have enabled the use of soluble organic bases instead of insoluble or strong inorganic bases that are traditionally employed. The single-phase nature of these reaction conditions facilitates their implementation in continuous flow systems, high-throughput optimization platforms, and large-scale applications. In this work, we utilized an automated microfluidic optimization platform to determine optimal reaction conditions for the couplings of an aryl triflate with four types of commonly employed amine nucleophiles: anilines, amides, primary aliphatic amines, and secondary aliphatic amines. By analyzing trends in catalyst reactivity across different reaction temperatures, base strengths, and base concentrations, we have developed a set of general recommendations for Pd-catalyzed crosscoupling reactions involving organic bases. The optimization algorithm determined that the catalyst supported by the dialkyltriarylmonophosphine ligand AlPhos was the most active in the coupling of each amine nucleophile. Furthermore, our automated optimization revealed that the phosphazene base BTTP can be used to facilitate the coupling of secondary alkylamines and aryl triflates. Chapter 4: The Quest for the Ideal Base: Rational Design of a Nickel Precatalyst Enables Mild, Homogeneous C-N Cross-Coupling Palladium-catalyzed amination reactions using soluble organic bases have provided a solution to the many issues associated with heterogeneous reaction conditions. Still, homogeneous C-N crosscoupling approaches cannot yet employ bases as weak and economical as trialkylamines. Furthermore, organic base-mediated methods have not been developed for Ni(0/II) catalysis, despite some advantages of such systems over analogous Pd-based catalysts. We designed a new air-stable and easily prepared Ni(II) precatalyst bearing an electron-deficient bidentate phosphine ligand that enables the cross-coupling of aryl triflates with aryl amines using triethylamine (TEA) as base. The method is tolerant of sterically-congested coupling partners, as well as those bearing base- and nucleophile-sensitive functional groups. With the aid of density functional theory (DFT) calculations, we determined that the electron-deficient auxiliary ligands decrease both the pK[subscript a] of the Ni-bound amine and the barrier to reductive elimination from the resultant Ni(II)-amido complex. Moreover, we determined that precluding Lewis acid-base complexation between the Ni catalyst and the base, due to steric factors, is important for avoiding catalyst inhibition.
Book Synopsis The Development of Palladium-catalyzed Cross-coupling Reactions of Allylic Silanolate Salts with Aromatic Bromides by : Nathan S. Werner
Download or read book The Development of Palladium-catalyzed Cross-coupling Reactions of Allylic Silanolate Salts with Aromatic Bromides written by Nathan S. Werner and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The palladium-catalyzed cross-coupling of allylic silanolate salts with a wide variety of aromatic bromides was developed. The coupling of sodium allyldimethylsilanolate and 2-butenyldimethylsilanolate required extensive optimization to deliver the expected products in high yields. The reaction of the allyldimethylsilanolate takes place at 85 °C under 0́ligand-less0́9 conditions in 1,2-dimethoxyethane with allylpalladium chloride dimer (2.5 mol %) to afford 730́395% yields of the allylation products. Both electron-rich and sterically hindered bromides reacted smoothly, whereas electron-poor bromides cross-coupled in poor yield because of a secondary isomerization to the 1-propeneyl isomer (or concommitant polymerization). A modified protocol that employs an electron-rich phosphine ligand (SPhos), a lower reaction temperature (40 °C), and a less polar solvent (toluene) delivers the expected products from electron-poor bromides without isomerization. The 2-butenyldimethylsilanolate (E/Z, 80:20) required additional optimization to maximize the formation of the branched (gamma-coupled) product and resulted in the development of two distinct protocols for gamma-selective coupling. The first protocol took advantage of a remarkable influence of added alkenes (dibenzylideneacetone and norbornadiene) and led to good selectivities for a large number of electron-rich and electron-poor bromides in 400́383% yields. However, bromides containing coordinating groups (particularly in the 2-position) gave lower, and in one case even reversed, site-selectivity. Electron-rich aromatic bromides reacted sluggishly under this protocol and led to lower product yields. The second protocol employed a sterically bulky phosphonium tetrafluoroborate salt (t-BuCy2PH+BF48́2) and resulted in 730́394% yields and excellent site-selectivity (gamma/alpha, 25:10́3>99:1) in the coupling of electron-rich, electron-poor, sterically hindered, and heteroaromatic bromides. The use of a configurationally homogeneous (Z)-silanolate and nontransferable diethyl groups were critical to achieving excellent results. A unified mechanistic picture involving initial gamma-transmetalation followed by direct reductive elimination or sigma0́3pi isomerization can rationalize all of the observed trends. The stereochemical course of palladium-catalyzed cross-coupling reactions of an enantioenriched, alpha-substituted, allylic silanolate salt with aromatic bromides was determined. The allylic silanolate salt was prepared in high geometrical (Z/E, 94:6) and high enantiomeric (94:6 er) purity by a copper-catalyzed SN20́9 reaction of a resolved carbamate. Eight different aromatic bromides underwent cross-coupling with excellent constitutional site-selectivity and excellent stereospecificity. Stereochemical correlation established that the transmetalation event proceeds through a syn SE0́9 mechanism with is interpreted in terms of an intramolecular delivery of the arylpalladium electrophile through a key intermediate that contains a discrete Si0́3O0́3Pd linkage. The catalytic, asymmetric palladium-catalyzed cross-coupling of sodium 2-butenylsilanolate with aromatic bromides was investigated. A wide range of chiral ligands including olefin, bidentate phosphine, monodentate phosphine, and cyclic and acyclic stereogenic at phosphorus ligands were evaluated. Commonly used chiral, bidentate phosphine ligands provided ineffective palladium-catalysts for the coupling of 2-butenyldimethylsilanolate with aromatic bromides. A catalyst derived from the monodentate phosphine ligand neomenthyldiphenylphosphine (20 mol %) and Pd(dba)2 (5 mol %) provided moderate enantioselectivity (75:25 er) and modest site-selectivity (5.7:1 gamma/alpha) in the coupling. Increased site-selectivity (up to>99:1) was obtained from reactions employing bulky di or trialkylphosphine ligands.
Book Synopsis Controlling Site-selectivity in Palladium-catalysed Cross-coupling Reactions Using Non-covalent Interactions Between Ligand and Substrate by : William Golding
Download or read book Controlling Site-selectivity in Palladium-catalysed Cross-coupling Reactions Using Non-covalent Interactions Between Ligand and Substrate written by William Golding and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
