Download or read book Synthesis and Application of New Chiral Peptides Guanidines and Formamides as Organocatalysts for Asymmetric C C Bond Formation Reactions written by Sunil Jagtap and published by . This book was released on 2006 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Enantioselective C C Bond Forming Reactions written by and published by Elsevier. This book was released on 2023-12-01 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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

Download or read book Polymeric Chiral Catalyst Design and Chiral Polymer Synthesis written by Shinichi Itsuno and published by John Wiley & Sons. This book was released on 2011-06-28 with total page 674 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reviews chiral polymer synthesis and its application to asymmetric catalysis. It features the design and use of polymer-immobilized catalysts and methods for their design and synthesis. Chapters cover peptide-catalyzed and enantioselective synthesis, optically-active polymers, and continuous flow processes. It collects recent advances in an important field of polymer and organic chemistry, with leading researchers explaining applications in academic and industry R & D.

Download or read book 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 published by . This book was released on 2021 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt: "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.

Download or read book Development and Evaluation of Chiral Catalysts for Asymmetric C C and C H Bond forming Reactions written by Christian Ebner and published by Cuvillier Verlag. This book was released on 2012-03-05 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Guanidines as Reagents and Catalysts I written by Philipp Selig and published by Springer. This book was released on 2017-04-18 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: The series Topics in Heterocyclic Chemistry presents critical reviews on present and future trends in the research of heterocyclic compounds. Overall the scope is to cover topics dealing with all areas within heterocyclic chemistry, both experimental and theoretical, of interest to the general heterocyclic chemistry community. The series consists of topic related volumes edited by renowned editors with contributions of experts in the field. All chapters from Topics in Heterocyclic Chemistry are published Online First with an individual DOI. In references, Topics in Heterocyclic Chemistry is abbreviated as Top Heterocycl Chem and cited as a journal

Download or read book 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 published by . This book was released on 2009 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Catalyzed Carbon Heteroatom Bond Formation written by Andrei K. Yudin and published by John Wiley & Sons. This book was released on 2010-12-01 with total page 541 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by an experienced editor widely acclaimed within the scientific community, this book covers everything fromo9xygen to nitrogen functionalities. From the contents: Palladium-Catalyzed Syntheses of Five-Member Saturated Heterocyclic and of Aromatic Heterodynes Palladium-Catalysis for Oxidative 1, 2-Difunctionalization of Alkenes Rhodium-Catalyzed Amination of C-H-Bonds Carbon-Heteroatom Bond Formation by RH(I)-Catalyzed Ring-Opening Reactions Transition Metal-Catalyzed Synthesis of Lactones and of Monocyclic and Fused Five-Membered Aromatic heterocycles the Formation of Carbon-Sulfur and Carbon-Selenium bonds by Substitution and Addition reactions catalyzed by Transition Metal Complexes New Reactions of Copper Acetylides Gold Catalyzed Addition of Nitrogen, Sulfur and Oxygen Nucleophiles to C-C Multiple Bonds. The result is an indispensable source of information for the Strategic Planning of the Synthetic routes for organic, catalytic and medicinal chemists, as well as chemists in industry.

Download or read book New Methods for Carbon carbon Bond Formation and Application to Organic Synthesis written by Christopher James Dockendorff and published by . This book was released on 2006 with total page 748 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Synthesis and Use of C2 symmetric Chiral Phenols for Asymmetric C C Bond Formation Using Organozinc Reagents written by Lai Chu Lin and published by . This book was released on 2002 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book New Organocatalytic Strategies for the Selective Synthesis of Centrally and Axially Chiral Molecules written by Nicola Di Iorio and published by Springer. This book was released on 2018-04-11 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis discusses the use of asymmetric organic catalysis for the direct enantioselective synthesis of complex chiral molecules, and by addressing the many aspects of both vinylogy and atropisomerism, it appeals to researchers and scholars interested in both areas. Organocatalysis is a relatively modern and “hot” topic in the chemical community; it is constantly expanding and its use has been extended to interesting areas like vinylogous reactivity and atropisomerism. Vinylogous systems are very important for their synthetic applications but also pose a number of challenges, the most notable of which are their reduced reactivity and the reduced stereocontrol at these positions. On the other hand, atropisomeric systems are even more important because of the huge potential they have as drugs, ligands and catalysts. Chemists have only recently “recognized” the importance of these two areas and are focusing their efforts on studying them and the challenges they pose. This thesis offers an extensive introduction on the general aspects of chirality and organocatalysis and an equally extensive experimental section that allow nonexperts to understand the discussion section and reproduce the experiments.

Download or read book Design Synthesis and Evaluation of Chiral Nonracemic Ligands and Catalysts for Asymmetric Synthesis written by Michael P. A. Lyle and published by . This book was released on 2005 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work described in this thesis concerns the design, synthesis and evaluation of new chiral nonracemic ligands and catalysts for use in asymmetric reactions. A series of chiral nonracemic chloroacetals were prepared from 2-chloro-4- methyl-6,7-dihydro-5H-[l]pyrindine-7-one and a variety of C2-symmetric and chiral nonracemic 1,2-ethanediols (R = Me, i-Pr and Ph). These chloroacetals were further elaborated, in a modular fashion, to provide a series of chiral ligands and catalysts. A new class of C2-symmetric 2,2'-bipyridyl ligands were prepared in one step fiom the chloroacetals via a nickel(0)-mediated homo-coupling reaction. These ligands were then evaluated as chiral directors in copper@)-catalyzed asymmetric cyclopropanation reactions of styrene and diazoesters (up to 44% ee). A chiral pyridine N-oxide and a C2-symmetric 2,2'-bipyridyl N, N'-dioxide were also prepared by direct oxidation of the corresponding pyridine and the 2,2'-bipyridine, respectively. These chiral N-oxides were evaluated as chiral catalysts in desymmeterization reactions of cis-stilbene oxide (up to 20% ee). A series of pyridylphosphine ligands (P, N-ligands) were subsequently prepared in two steps from the chloroacetals via a Suzuki coupling reaction with orthofluorophenylboronic and on subsequent displacement of the fluoride with the potassium anion of diphenylphosphine. These ligands were then evaluated in palladium-catalyzed asymmetric allylic substitution reactions of racemic 3-acetoxy-l,3-diphenyl-1-propene with dimethyl malonate. Optimization of the reaction conditions resulted in the formation of the alkylated product in excellent yield (91%) and in high enantiomeric excess (90%). A related chiral nonracemic and C2-symmetric 2,2'-bipyridyl ligand was prepared from 2-chloro-4-methyl-5H-[llpyrindine. This pyrindine was prepared from a common intermediate that was used in the synthesis of the first generation of ligands. The chirality of this second generation ligand was installed by a Sharpless asymmetric dihydroxylation reaction (90% ee). The subsequently elaborated 2,2'-bipyridyl ligand (enriched to>99% ee) was then evaluated in copper(1)-catalyzed asymmetric cyclopropanation reactions of alkenes and diazoesters. In the case of the reaction of para-fluorostyrene and tert-butyl diazoacetate, the corresponding cyclopropane was formed in good diastereoselectivity (92:8) and in excellent enantioselectivity (99% ee). This ligand was also evaluated in copper(I1)-catalyzed asymmetric Friedel-Crafts alkylation reactions of various substituted indoles (up to 90% ee) and in copper(1)- catalyzed asymmetric allylic oxidation reactions of cyclic alkenes with tert-butyl peroxybenzoate (up to 9 1 % ee).

Download or read book Synthesis and Application of New Chiral Ligands for Enantioselectivity Tuning in Transition Metal Catalysis written by Fanji Kong and published by . This book was released on 2017 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Recent Advances in Guanidine Based Organocatalysts in Stereoselective Organic Transformation Reactions written by Shrawan Kumar Mangawa and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book 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 published by . This book was released on 2011 with total page 253 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Development and Application of Carbon carbon Bond Forming Methodologies written by Joshua Aaron Bishop and published by . This book was released on 2011 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The construction of novel small molecules is an invaluable tool to the fields of chemical biology and drug discovery. Information gained from introducing unique chemical moieties to biological systems allows for a better understanding of the governing dynamics of cellular mechanisms leading to new treatments for disease. The only way to explore uncharted biological space is by discovering and producing new chemical structures. The work described herein discusses the development and application of novel chemical methodologies to arrive at unique small molecules. An organocatalytic, asymmetric addition of carbon nucleophiles to prochiral aldimines was developed. This transformation capitalizes on the inherent properties of boron to promote a ligand exchange with chiral dials generating a chiral nucleophile in situ . Mechanistic studies were carried out to garner a better understanding of this transformation. Propargyl, vinyl and aryl substituted amides are generated in high chemical yield and as single enantiomers. The transformation yields synthetically useful chiral building blocks as shown through the formal synthesis of the known pharmaceutical Xyzal©. Reaction discovery implementing a series of propargyl amides lead to the development of unique Ag catalyzed 5- exo and 6-endo cyclizations to produce novel oxazolines and oxazines respectively. A novel, asymmetric formal [3+2] cycloaddition utilizing substituted isocyanoacetates as stabilized dipoles was invented. The transformation yields chemically unique nitrogen containing heterocycles with two stereogenic centers. The stereochemical outcome of the process is controlled through the choice of ligand to arrive at either the anti or syn dihydro-pyrrolidine product. The transformation represents the first reported application of a Ag/Trost ligand complex for a chemical process. As such, mechanistic investigations were carried out to illuminate the catalytic cycle. The synthesis and application of the first small molecule inhibitor of transcription factor LSF is discussed. The isoquinolinone scaffolds were modified from a medicinal chemistry standpoint to optimize the pharmacophore. Synthetic pathways, structure activity relationships and solubility characteristics of the isoquinolinones were addressed. A pharmacokinetic analysis was done to determine a metabolic pathway and rate of metabolism of the lead compound in vitro . These unique small molecules are shown to have u M activity in vivo against human hepatocellular carcinoma cell lines with no signs of toxicity and u M activity in vitro against both 3T3 and HeLa cell lines.

Download or read book Development of New Transition Metal Catalyzed C C Bond Forming Reactions and Their Application Toward Natural Product Synthesis written by Abbas Hassan and published by . This book was released on 2011 with total page 670 pages. Available in PDF, EPUB and Kindle. Book excerpt: In Michael J. Krische research group we are developing new transition metal catalyzed Carbon-Carbon (C-C) forming reactions focusing on atom economy and byproduct free, environmental friendly approaches. We have developed a broad family of C-C bond forming hydrogenations with relative and absolute stereocontrol which provide an alternative to stoichiometric organometallic reagents in certain carbonyl and imine additions. Inspiring from the group work my goal was to develop new reactions, extend the scope of our group chemistry and their application towards synthesis of biologically active natural products. I have been part of enantioselective Rh catalyzed Aldol reaction of vinyl ketones to different aldehydes. Also, we have found that iridium catalyzed transfer hydrogenation of allylic acetates in the presence of aldehydes or alcohols results in highly enantioselective carbonyl allylation under the conditions of transfer hydrogenative. Based on this reactivity a concise enantio- and diastereoselective synthesis of 1,3-polyols was achieved via iterative chain elongation and bidirectional iterative asymmetric allylation was performed, which enables the rapid assembly of 1,3-polyol substructures with exceptional levels of stereocontrol. The utility of this approach stems from the ability to avoid the use of chirally modified allylmetal reagents, which require multistep preparation, and the ability to perform chain elongation directly from the alcohol oxidation level. This approach was utilized for the total synthesis of (+)-Roxaticin from 1,3-propanediol in 20 longest linear steps and a total number of 29 manipulations. Further, advancements were made in iridium catalyzed C-C bond formation under transfer hydrogenation. While methallyl acetate does not serve as an efficient allyl donor, the use of more reactive leaving group in methallyl chloride compensate for the shorter lifetime of the more highly substituted olefin [pi]-complex. Based on this insight into the requirements of the catalytic process, highly enantioselective Grignard-Nozaki-Hiyama methallylation is achieved from the alcohol or aldehyde oxidation levels. Also, a catalytic method for enantioselective vinylogous Reformatsky- type aldol addition was developed in which asymmetric carbonyl addition occurs with equal facility from the alcohol or aldehyde oxidation level. Good to excellent levels of regioselectivity and uniformly high levels of enantioselectivity were observed across a range of alcohols and aldehydes.