Investigations Into the Palladium and Rhodium Catalyzed Ring Opening Reactions of C1-Substituted Oxabicyclic Alkenes PDF Download
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Author: Michael Edmunds
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Languages : en
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Author: Michael Edmunds
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Languages : en
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Author: Christine Le
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Languages : en
Pages : 0
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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.
Author: Raheem Mohammed Abdul
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Languages : en
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Author: Kelsey Jack
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Languages : en
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Author: Jane Panteleev
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Languages : en
Pages : 1112
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Author: Christopher Wicks
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Languages : en
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Oxabenzonorbornadiene (OBD) and derivatives thereof have become key substrates of interest within synthetic organic chemistry and natural product synthesis as they enable the formation of multiple stereocenters in a single transformation. The present work expands on previous studies to investigate various intramolecular transformations, and regiochemical implications regarding ring-opening reactions of asymmetric oxabicyclic alkenes. Acid-catalyzed intramolecular ring-opening reactions of cyclopropanated oxabenzonorbornadiene (CPOBD) derivatives were investigated to afford novel medium-sized ring systems in moderate to good yields and good to excellent regioselectivity. Similarly, a Ni catalyzed intramolecular ring-opening reaction of alkyl halide tethered OBD compounds was optimized, thus generating a naphthalene derivative in excellent yields. Lastly, iridium-catalyzed ring-opening reactions of unsymmetrical C1-substituted OBD derivatives is presented using alcohols and water as nucleophiles which allows for the selective synthesis of previously inaccessible substrates.
Author: Lei Zhang
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Languages : en
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This thesis describes the development of rhodium-catalyzed asymmetric ring opening of strained alkenes and the subsequent use of rhodium and palladium catalysis in the development of domino reactions. The contents are divided into 4 chapters. Chapter 1 describes the rhodium-catalyzed asymmetric ring opening (ARO) of strained bicyclic alkenes using silyl enolates. The development of this method achieved a highly enantioselective addition of alkyl fragments onto bicyclic alkenes, affording broad scope, mild reaction conditions, and high functional group tolerance. The synthetic utility of the method was demonstrated through functionalization of the ARO products to a number of core scaffolds of natural products. Chapter 2 describes the development of a domino rhodium/palladium-catalyzed synthesis of dihydroquinolines. The use of two different ligands in the reaction led to a mechanistic investigation that revealed metal-ligand interactions that were crucial to the success of this domino reaction. The mechanistic insights facilitated reaction optimization, leading to an expansion of the reaction scope, including the synthesis of chromenes. Chapter 3 describes the importance of time resolution and ligand interference in the development of enantioselective domino rhodium/palladium catalysis employing chiral and achiral ligands. The development of this method provided access to chiral C4-substituted dihydroquinolinones in a direct manner, affording high yields and enantioselectivities. Current work on developing multicomponent enantioselective rhodium/palladium catalysis is also disclosed. Chapter 4 describes the development of multi-metal-catalyzed multicomponent reactions (MC)2R. The development of a highly compatible rhodium/palladium catalyst system allowed the incorporation of a third catalyst, copper, achieving a three-component one-pot reaction. Current work on the development of the use of other metal combinations to achieve (MC)2R is also disclosed.
Author: Montserrat Diéguez
Publisher: John Wiley & Sons
ISBN: 3527804072
Category : Technology & Engineering
Languages : en
Pages : 431
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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.
Author: Carl Bernard Ziegler
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Category : Alkenes
Languages : en
Pages : 192
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Author: Keith Fagnou
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Languages : en
Pages : 0
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Oxabenzonorbornadienes were shown to undergo asymmetric ring opening with a variety of alcohol, phenol and activated amine nucleophiles in the presence of catalytic amounts of [Rh(COD)Cl]2 and chiral diphosphine ligands. The product dihydronaphthalenols were produced in 73-99%ee. Extension of this methodology to 'o'-halophenols required changing the rhodium source to [Rh(CO)2Cl]2. These products were applied to the synthesis of benzodihydrofurans. In order for carboxylates and unactivated amines to induce ring opening, the addition of a proton source was required. Enantioselectivities of up to 74% and 81% were observed for the amine and the carboxylate ring opened products respectively. These products were applied towards the synthesis of 1,4-dihydronaphthalenols. Vinyl Epoxides were shown to undergo diastereoselective ring opening reaction with alcohols and aromatic amine nucleophiles in the presence of catalytic amounts of [Rh(CO)2Cl]2. The 'trans '-1,2-alkoxyalcohols and aminoalcohols were produced in >80% yield and >20:1 diastereoselectivity.
