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Rhodium Catalyzed Enantioselective Desymmetrizations Of Oxabicyclic Alkenes And Alkene Difunctionalization Via Nickel Catalyzed Arylcyanation
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Book Synopsis Rhodium-Catalyzed Enantioselective Desymmetrizations of Oxabicyclic Alkenes and Alkene Difunctionalization Via Nickel-Catalyzed Arylcyanation by : Andy Wei Jen Yen
Download or read book Rhodium-Catalyzed Enantioselective Desymmetrizations of Oxabicyclic Alkenes and Alkene Difunctionalization Via Nickel-Catalyzed Arylcyanation written by Andy Wei Jen Yen and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Development of Rhodium-Catalyzed Reactions for The Enantioselective Desymmetrization and Carbonylation of Meso Alkenes by : Frederic Menard
Download or read book Development of Rhodium-Catalyzed Reactions for The Enantioselective Desymmetrization and Carbonylation of Meso Alkenes written by Frederic Menard and published by . This book was released on 2010 with total page 674 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the discovery of catalytic reactions that create carbon-carbon bonds stereoselectively between substrates bearing an alkene and organoboronic acids reagents. Chiral rhodium(I) catalysts were found to react with various meso-symmetrical substrates, thereby resulting in enantioselective desymmetrization reactions. The methodologies presented herein allow the rapid synthesis of several chiral functionalized molecules; including branched homoallylic alcohols, cyclopentenyl hydrazines, and ketohydrazines.Finally, Chapter 4 outlines the development of a mild catalytic acylation of pi systems. This mode of reactivity was optimized to promote the desymmetrization of [2.2.1]-diazabicycles via a formal allylic substitution with acyl anions as nucleophiles. The method yields densely functionalized trans-2-ketocyclopent-3-enyl hydrazides. In addition, preliminary studies demonstrate that the rhodium(I)-catalyzed acyl anion addition is also possible with other pi electrophiles. For example, with alkyne, it provided a synthesis of cyclopentenones that complements the Pauson-Khand reaction. Overall, the catalytic transformations reported herein give access to seven classes of products stereoselectively; starting from simple reagents.The thesis is divided according to three main transformations: asymmetric allylic substitution of allylic carbonates, asymmetric ring-opening of [2.2.1]-diazabicyles, and carbonylation of alkenes or alkynes. Chapter 2 details the investigations of a ligand-controlled catalytic process to prepare either trans-2-arylcyclopent-3-enols (up to 94% ee), or trans-4-arylcyclopent-2-enols (up to 99% ee) as the major products starting from cyclic meso allylic dicarbonates. This rhodium-catalyzed methodology was extended to include linear allylic dicarbonates, thereby yielding chiral 2-arylbut-3-enols with up to 95% ee.An enantioselective desymmetrization of strained alkenes by ring-opening of meso bicyclic hydrazines is described in Chapter 3. The reaction allows one to prepare trans-2-arylcyclopent- 3-enyl hydrazides with up to 99% ee. In addition, an enantioselective hydroarylation process was identified to yield 5-aryl-2,3-diazabicyclo[2.2.1]heptanes. Mechanistic investigations showed that the reaction proceeds via an unusual C-H activation/1,4-migration of the rhodium catalyst.
Book Synopsis Development of Copper-catalyzed Enantioselective Alkene Difunctionalization Reactions Via Radical Intermediates by :
Download or read book Development of Copper-catalyzed Enantioselective Alkene Difunctionalization Reactions Via Radical Intermediates written by and published by . This book was released on 2015 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
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.
