Synthesis And Application Of New Chiral Peptides Guanidines And Formamides As Organocatalysts For Asymmetric C C Bond Formation Reactions
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Synthesis And Application Of New Chiral Peptides Guanidines And Formamides As Organocatalysts For Asymmetric C C Bond Formation Reactions
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Author : Sunil Jagtap
language : en
Publisher:
Release Date : 2006
Synthesis And Application Of New Chiral Peptides Guanidines And Formamides As Organocatalysts For Asymmetric C C Bond Formation Reactions written by Sunil Jagtap and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
Enantioselective C C Bond Forming Reactions
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Author :
language : en
Publisher: Elsevier
Release Date : 2023-12-01
Enantioselective C C Bond Forming Reactions written by and has been published by Elsevier this book supported file pdf, txt, epub, kindle and other format this book has been release on 2023-12-01 with Science categories.
Enantioselective C-C Bond Forming Reactions: From Metal Complex-, Organo-, and Bio-catalyzed Perspectives, Volume 73 in the Advances in Catalysis series, highlights new advances in the field, with this new volume presenting interesting chapters on topics such as An introduction to Chirality, Metal-catalyzed stereoselective C-C-bond forming reactions, Enantioselective C-C bond forming reactions promoted by organocatalysts based on unnatural amino acid derivatives, Enantioselective C-C bond formation in complex multicatalytic system, Gold-based multicatalytic systems for enantioselective C-C Bond forming reactions, Novel enzymatic tools for C-C bond formation through the development of new-to-nature biocatalysis, and more. Provides the authority and expertise of leading contributors from an international board of authors Presents the latest release in Advances in Catalysis serials Updated release includes the latest information in the field
The Development Of New Direct And Asymmetric Ni Ii Catalysed Carbon Carbon Bond Forming Reactions And Their Application To Total Synthesis
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Author : Stuart Kennington
language : en
Publisher:
Release Date : 2021
The Development Of New Direct And Asymmetric Ni Ii Catalysed Carbon Carbon Bond Forming Reactions And Their Application To Total Synthesis written by Stuart Kennington and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with categories.
"This thesis focuses on the search for new methodologies for the direct, stereoselective and catalytic formation of carbon-carbon bonds through the formation of chiral nickel(II) enolate species and the application of such methods to the synthesis of natural products. The project starts with the stereocontrol coming from chiral auxiliaries, developed first by Evans and then later by Crimmins and Nagao, following the previous experience and expertise of the research group. These auxiliaries have proved to be a reliable and high yielding option to afford excellent levels of stereocontrol in various reactions. Furthermore, they can be removed after such processes to leave enantiopure synthons. However, they do have their drawbacks, one being the inability of synthesising all of the available stereoisomers from one starting material. To combat this issue, the second part of the thesis is centred around the development of a new methodology based on achiral starting materials (scaffolds) with chiral nickel(II) complexes, which both enable the reaction and control its stereochemical outcome.In the first Chapter, methods previously developed in the group were applied to the synthesis of a fragment of the marine sponge macrolide Peloruside A, which has shown to have anticancer activity, especially against leukaemia. Three key steps involve reactions based on the use of chiral auxiliaries that had been developed in the group: a nickel catalysed reaction with trimethyl orthoformate, a titanium-mediated acetate aldol reaction, and a titanium-mediated addition of an acetate enolate to an acetal. The overall yield of the synthesis of the target fragment C9-C19 was 24% over 14 steps.Chapter 2 presents a new reaction based on the addition of enolates, generated from chiral N-acyl thiazolidinethiones with an achiral nickel(II) complex, to stable carbocationic salts. This alkylation reaction was first thoroughgoingly optimised and later applied to a large range of substrates with wide success. Moreover, it was applied to a highly challenging electrophile successfully which lead to the discovery of a reversible alkylation process. The products were also transformed via the removal of the auxiliary to leave a variety of functional groups.In Chapter 3 the stereocontrol is passed from the starting material to the catalyst in an ambitious advancement of the group's chemistry. After an extensive study of potential achiral scaffolds to provide the platform for the reactions and chiral diphosphine ligands to provide the enantiocontrol, we observed the best scaffold was the 6-memberd thiazinanethione structure and the best ligand DTBM-SEGPHOS®. We were able to apply this methodology to the reaction of: trimethyl orthoformate (an oxocarbenium precursor), tropylium tetrafluoroborate (a cationic salt), a diaryl methyl ether (a carbenium precursor), and also a more complex diaryl ketal electrophile with high yields and exceptional control over the one stereocentre formed. Furthermore, using a dimethyl acetal we were able to exert some control over the relative configuration of two stereocentres whilst maintaining exceptional enantioselectivity. Calculations and elucidation of the configuration of the new stereocentre formed support our hypothesis for the mechanism for such a process. We also demonstrated the ease with which the scaffold can be removed and were able to synthesise a wide variety of synthons with differing functional groups. Finally, we were able to scale up and apply the methodology to the synthesis of Peperomin D, a five membered lactone containing two stereocentres.Finally, in the last Chapter we present a new methodology for the asymmetric aldol reaction of N-acyl thiazinanethiones with aromatic aldehydes catalysed by a chiral nickel (II) complex, which involves the simultaneous silyl protection of the adducts. This new reaction proceeds through an open transition state and leads to the anti-aldol products. We were able to optimise the reaction to achieve a high diastereoselectivity, exceptional enantioselectivity, and excellent yield. Furthermore, we were able to apply the conditions to various aromatic aldehydes and N-acyl thiazinanethiones. Finally, the scope of the reaction was expanded to three different electrophiles, opening new lines of investigation" -- TDX.
Development And Evaluation Of Chiral Catalysts For Asymmetric C C And C H Bond Forming Reactions
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Author : Christian Ebner
language : en
Publisher: Cuvillier Verlag
Release Date : 2012-03-05
Development And Evaluation Of Chiral Catalysts For Asymmetric C C And C H Bond Forming Reactions written by Christian Ebner and has been published by Cuvillier Verlag this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-03-05 with Science categories.
This work was dedicated to the development and evaluation of new chiral catalysts for asymmetric C-C and C-H bond forming reactions. In the first part of the thesis an ESI-MS screening method is described, which allows the determination of a chiral catalyst´s selectivity in the palladium catalyzed asymmetric allylic alkylation by testing its racemic form. The value of this new method was demonstrated when different new aryl-PHOX-type ligands, which are not easily accessible in their enantiopure form, were evaluated. In the second part new PHOX-type ligands were tested in the iridium-catalyzed asymmetric hydrogenation of different unsaturated compounds. Although low activities and selectivities were found in most cases, one ligand showed promising results in the hydrogenation of allylic alcohols and imines. Furthermore air- and moisture-stable secondary phosphine oxide (SPO) containing bidentate ligands were tested in the palladium-catalyzed asymmetric allylic alkylation reaction. SPO,N-ligands bearing a PHOX type backbone were inactive in this transformation as they tend to form inactive palladium-bis-ligand complexes. SPO,P ligands however, were able to promote the desired reaction in a highly selective fashion although only low activities were found. During this work as well a new organo-catalyst, based on the structure of 2,3-dihydrobenzo[1,4]oxazine, was developed which allows for the asymmetric organo-catalyzed transfer-hydrogenation of α,β-unsaturated aldehydes. This catalyst was able to reduce for the first time β, β-diaryl acrylaldehydes with very good activities and high enantioselectivities. Moreover an ESI-MS based mechanistic study on the tripeptide catalyzed conjugate addition reaction of aldehydes to nitroolefins was carried out. By this all reaction intermediates postulated for an enamine mechanism have been detected. Furthermore the attack of the enamine onto the nitroolefin was found to be the selectivity determining step in this process. The last part of this work aimed for the asymmetric α -allylation of carbonyl compounds by a tandem-catalysis approach. An intensive screening of both the organo-catalyst and the palladium-ligand led to reaction conditions which allowed for the selective mono-allylation of ketones in high yields. The formation of a quaternary center by α -allylation of α -branched aldehydes was also achieved. However, only low enantiomeric excesses were obtained in this transformation for the different catalyst systems tested.
Applications Of Chiral Guanidine Organocatalysts In Asymmetric Transformations Probing Structure Activity Relationships Of Artificial Enzyme Active Sites And Development Of Metal Free Oxidative Cyclization Reactions
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Author : Helena M. Lovick
language : en
Publisher:
Release Date : 2009
Applications Of Chiral Guanidine Organocatalysts In Asymmetric Transformations Probing Structure Activity Relationships Of Artificial Enzyme Active Sites And Development Of Metal Free Oxidative Cyclization Reactions written by Helena M. Lovick and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with Asymmetric synthesis categories.
New Methods For Carbon Carbon Bond Formation And Application To Organic Synthesis
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Author : Christopher James Dockendorff
language : en
Publisher:
Release Date : 2006
New Methods For Carbon Carbon Bond Formation And Application To Organic Synthesis written by Christopher James Dockendorff and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
Tetralins with a desired 1,4-substitution pattern were synthesized via Diels-Alder reactions between arynes and acyclic dienes. We have shown this underutilized reaction to be useful for the stereospecific synthesis of 1,4-dihydronaphthalenes which are not readily accessible via other methods. Preliminary efforts to render this reaction asymmetric are presented; excellent diastereoselectivities were observed using Oppolzer's sultam as a chiral auxiliary on the diene. A short synthesis of racemic sertraline was also carried out using the aryne Diels-Alder reaction as the key step. We have reported the rhodium-catalyzed asymmetric ring-opening reaction of oxabicyclic alkenes with aryl- and alkenylboron nucleophiles. The reactions generally proceed with excellent yield and enantioselectivity under mild conditions, giving only one diastereomer (cis adducts). The Rh(I) catalyst system utilizes the ferrocenyl bisphosphine ligand PPF-P(t-Bu) 2. This ligand is also very efficient for the ring-opening reactions with heteroatom nucleophiles, which proceed via a different mechanism and give trans products. We have recently discovered that other Rh(I) catalysts can promote the highly enantio- and regioselective desymmetrization of meso-diols via allylic substitution reactions with organoborons. Some of the limitations of the rhodium-catalyzed ring-opening reactions were overcome by the development of Pd(II) catalyst systems. These catalysts give excellent yields (albeit currently with decreased enantioselectivities relative to the rhodium reactions) under very mild conditions (undistilled methanol, room temperature, open to the air). The Pd(II) systems also work very well with azabicyclic alkenes and with heteroaryl- and ortho -substituted arylboronic acids, which all were problematic with rhodium catalysts. They also show some promise with alkylboron species. Various metal-catalyzed ring-opening reactions have been utilized to make gram-scale tetralin scaffolds for drug discovery efforts. The scaffolds were subsequently functionalized to yield libraries of amides, amines, and ureas for screening against a variety of biological targets. Several opioid receptor antagonists were subsequently identified by our industrial collaborators.
Recent Advances In Guanidine Based Organocatalysts In Stereoselective Organic Transformation Reactions
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Author : Shrawan Kumar Mangawa
language : en
Publisher:
Release Date : 2016
Recent Advances In Guanidine Based Organocatalysts In Stereoselective Organic Transformation Reactions written by Shrawan Kumar Mangawa and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with Science categories.
Tremendous efforts have been put toward the design and synthesis of newer enantioselective organocatalysts for the enanatioselective synthesis. Recently, guanidine-containing chiral organocatalysts have attracted considerable attention due to their ease of synthesis and high enantioselective catalytic activities. This chapter highlights the successive development of chiral guanidine organocatalysts in asymmetric organic transformation reactions in the past few decades.
Synthesis And Use Of C2 Symmetric Chiral Phenols For Asymmetric C C Bond Formation Using Organozinc Reagents
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Author : Lai Chu Lin
language : en
Publisher:
Release Date : 2002
Synthesis And Use Of C2 Symmetric Chiral Phenols For Asymmetric C C Bond Formation Using Organozinc Reagents written by Lai Chu Lin and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2002 with categories.
ABSTRACT: Several C2-symmetric chiral phenols were synthesized from derivatives of natural products (1R,2S)-ephedrine, (1S,2S)-pseudoephedrine and (L)-proline. The use of these ligands for asymmetric alkylation of benzaldehyde, Cu-catalyzed and Ni-catalyzed conjugate addition to chalcone using diethylzinc were explored. Moderate enantiomeric excess of 37% was obtained in the alkylation of benzaldehyde, whereas 60% ee and ̃40% ee were obtained for the Ni-catalyzed and Cu-catalyzed conjugate addition to chalcone, respectively, with moderate yields in all cases. Although these ligands were shown not be very efficient chiral catalysts for these types of reactions, they provided some structural information for future improvement on design of chiral auxiliaries for asymmetric induction.
Synthesis And Applications Of New Chiral Organocatalysts Based On Cis 1 2 Diaminocyclohexane And Asymmetric Nozaki Hiyama Allylation Of Aldehydes
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Author : Mei Ching Ong
language : en
Publisher:
Release Date : 2011
Synthesis And Applications Of New Chiral Organocatalysts Based On Cis 1 2 Diaminocyclohexane And Asymmetric Nozaki Hiyama Allylation Of Aldehydes written by Mei Ching Ong and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Synthesis And Application Of New Chiral Ligands For Enantioselectivity Tuning In Transition Metal Catalysis
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Author : Fanji Kong
language : en
Publisher:
Release Date : 2017
Synthesis And Application Of New Chiral Ligands For Enantioselectivity Tuning In Transition Metal Catalysis written by Fanji Kong and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with Chirality categories.
A set of five new C3-symmetric phosphites were synthesized and tested in palladium-catalyzed asymmetric Suzuki coupling. The observed reactivity and selectivity were dependent upon several factors. One of the phosphites was able to achieve some of the highest levels of enantioselectivity in asymmetric Suzuki couplings with specific substrates. Different hypotheses have been made for understanding the ligand effects and reaction selectivities, and those hypotheses were tested via various methods including DOSY NMR experiments, X-ray crystallography, and correlation of catalyst selectivity with Tolman cone angles. Although only modest enantioselectivities were observed in most reactions, the ability to synthesis these phosphites in only three steps on gram scales and to readily tune their properties by simple modification of the binaphthyl 2́-substituents makes them promising candidates for determining structure-selectivity relationships in asymmetric transition metal catalysis, in which phosphites have been previously shown to be successful. A series of novel chiral oxazoline-based carbodicarbene ligands was targeted for synthesis. Unfortunately, the chosen synthetic route could not be completed due to unwanted reactivity of the oxazoline ring. However, a new and efficient route for Pd-catalyzed direct amination of aryl halides with oxazoline amine was developed and optimized during these studies. Chiral binaphthyl based Pd(II) ADC complexes with different substituent groups have been synthesized and tested in asymmetric Suzuki coupling reactions. Although only low enantioselectivities were observed in Suzuki coupling, this represents a new class of chiral metal-ADC catalysts that could be tested in further catalytic.