Rhodium Catalysed Asymmetric Ring Opening of Oxabicyclic Alkenes and Diastereoselective Ring Opening of Epoxides with Heteroatom Nucleophiles PDF Download
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Languages : en
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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.
Author: A. C. Knipe
Publisher: John Wiley & Sons
ISBN: 0470061235
Category : Science
Languages : en
Pages : 644
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The only book series to summarize the latest progress on organic reaction mechanisms, Organic Reaction Mechanisms, 2003 surveys the development in understanding of the main classes of organic reaction mechanisms reported in the primary scientific literature in 2003. The 39th annual volume in this highly successful series highlights mechanisms of stereo-specific reactions. Reviews are compiled by a team of experienced editors and authors, allowing advanced undergraduates, graduate students, postdocs, and chemists to rely on the volume's continuing quality of selection and presentation.
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: Andy Wei Jen Yen
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Languages : en
Pages : 0
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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.
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Author: P. Andrew Evans
Publisher: John Wiley & Sons
ISBN: 352760409X
Category : Science
Languages : en
Pages : 496
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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.
Author: Karl B. Hansen
Publisher:
ISBN:
Category : Asymmetric synthesis
Languages : en
Pages : 200
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![Rhodium-catalyzed Ring Opening of Vinyl Epoxides and Vinyl Aziridines with Aniline Nucleophiles [microform] PDF](https://books.google.com/books/content/images/frontcover/O9tKjwEACAAJ?fife=w80-h100)
Author: Jasmine Almas
Publisher: National Library of Canada = Bibliothèque nationale du Canada
ISBN: 9780612738416
Category :
Languages : en
Pages : 288
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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.
