Download or read book C2 and C3 Symmetric Chiral Bis and Tris phosphines in Asymmetric Catalysis written by Zhiming Xu and published by . This book was released on 2017 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1. Effect of linker length on selectivity and cooperative reactivity in platinum-catalyzed asymmetric alkylation of bis(phenylphosphino)alkanes. The selectivity of catalytic asymmetric transformations of bifunctional symmetrical substrates often depends on the linker between the two reactive sites. If the catalyst controls the selectivity of reactions at both sites, the rac product will be formed in high enantiomeric ratio (er) via asymmetric amplification. Substrate control may augment this selectivity (positive cooperativity) or detract from it (negative cooperativity). We investigated the effect of linker length on the selectivity of catalytic asymmetric alkylation of the bis(secondary phosphines) PhHP-(CH2)[subscript n]PHPh (n = 2-6, 1a-e) with benzyl bromide using the base NaOSiMe3 and the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl). The two alkylations of bis(secondary phosphines) 1b-e with longer linker lengths (n = 3-6) showed identical selectivity, within experimental error. This catalyst control resulted in asymmetric amplification of rac-2. In contrast, the selectivity of the first alkylation of ethano-bridged 1a was lower than that in 1b-e (negative cooperativity), but the selectivity of the second alkylation increased due to positive cooperativity. I developed an efficient synthesis of the intermediate PhHP(CH2)2PPh(CH2Ph) (3a), which was required for determination of the selectivity of both steps in Pt-catalyzed alkylation of 1a. Possible mechanistic explanations for the observed dependence of selectivity on linker length are discussed in this chapter. Chapter 2. Selective formation of a C3-symmetric P-stereogenic tris(phosphine) via platinum-catalyzed asymmetric alkylation of a tris(secondary phosphine). C2-symmetric bis(phosphines) are the most common and successful ligands for metal-catalyzed reactions. Considering the great success of C2-symmetric ligands in asymmetric catalysis, C3-symmetric chiral tris(phosphines) were proposed to be useful in octahedral complexes, creating three homotopic sites. However, very little is known about C3-symmetric tris(phosphines) and their applications, mostly because of the lack of synthetic routes. We used Pt-catalyzed asymmetric alkylation to prepare enantiomerically enriched C3-symmetric, P-stereogenic tripodal tris(phosphines) from the tris(secondary phosphine) MeC(CH2PHPh)3 (5 a racemic mixture of C1- and C3-symmetric diastereomers) and a benzl bromide, utilizing the Pt((R,R)-Me-Duphos)(Ph)(Cl) catalyst precursor and a base. Pt-catalyzed alkylation of MeC(CH2PHPh)3 (5) with 2-cyanobenzyl bromide gave a mixture of tris(phosphines) MeC(CH2PPh(CH2Ar))3 (6) enriched in C3-6; oxidation of 6 by sulfur or H2O2 formed phosphine sulfide S-6 and oxide O-6. Hydrogen bonding between O-6 and the chiral amino acid (S)-Fmoc-Trip(BOC)-OH leads to the formation of new diastereomers. By integrating the 31P NMR spectra, I measured the dr and er values. Tris(phosphine) 6 was formed with a disatereomeric ratio (dr - C3/C1) of 2.1(2) and enantiomeric ratios of 54(10) and 3.8(7) for C3-3 and C1-3 respectively, which showed that the selectivity of the triple alkylation was not the same at each site (substrate control). Chapter 3. Screening racemic catalysts provides information on selectivity and mechanism in platinum-mediated asymmetric alkylation of bis- and tris(secondary phosphines). Screening racemic catalysts for transformations of symmetrical bifunctional substrates can provide information on the selectivity of an enantiopure catalyst. This idea was extended to Pt-catalyzed asymmetric alkylation of the bis(secondary phosphines) PhHP(CH2)3PHPh and PhHPCH2CMe2CH2PHPh and the tris(phosphine) MeC(CH2PHPh)3 with benzyl bromides using the catalyst precursors Pt(Me-DuPhos)(Ph)(CI) and Pt(BenzP*)(Ph)(CI). Depending on the catalyst and the substrate, these reactions occured under catalyst control without dissociation of the substrate, or under substrate control with or without substrate dissociation. The resulting structure-selectivity relationships provided mechanistic information. Chapter 4. Synthesis of new chiral bis(phospholane) metal-pincer complexes. Metal pincer complexes have received great attention in recent years as robust catalyst precursors. However, chiral metal pincer complexes for application in asymmetric catalysis are rare. Dialkylphospholane groups have an outstanding track record in asymmetric catalysis (commercial DuPhos and BPE ligands) and their steric properties can be easily controlled by tuning the alkyl substituents on the phospholane ring. These donors have similar steric and electronic properties to the common used bulky dialkylphosphine groups (P(t-Bu)2, P(i-Pr)2, etc.). Optimization of the synthesis of chiral PCP ligands bearing such phospholane groups and investigation of their coordination chemistry are discussed in this chapter.

Download or read book Asymmetric Catalysis with a C2 symmetric Bisoxazolidine and Enantioselective Sensing Using Axially Chiral Diacridylnaphthalenes written by Shuanglong Liu and published by . This book was released on 2008 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Handbook Of Chiral Chemicals written by David John Ager and published by CRC Press. This book was released on 1999-01-04 with total page 395 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describes the problems associated with large, commercial-scale syntheses of chiral molecules and the relatively small number of reactions that can be used to achieve these syntheses. The book discusses commercially viable and still-developing methods of compound manufacture, and reviews the best-selling chiral compounds as of 1996.

Download or read book C2 symmetric Bis phosphines and Their Metal Complexes written by Matthew David Sanderson and published by . This book was released on 2015 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Chapter 1: The dimethylation of the C2-symmetric Pt-phosphido complex Pt((R,R)-Me-DuPhos)(IsPCH2PIs) (Is = 2,4,6-(iPr)3C6H2) to yield rac and meso [Pt((R,R)-Me-DuPhos)(IsMePCH2PMeIs)][OTf]2 represents an interesting case of the Horeau principle as applied to chiral bifunctional substrates. Tim Chapp initially synthesized these complexes, but a rational synthesis of meso-IsMePCH2PMeIs, which was needed for independent synthesis of the metal complexes, could not be found. The synthesis and isolation of rac-IsMePCH2PMeIs is reproducible on a large scale. While meso-IsMePCH2PMeIs could be prepared in a highly enriched form (dr = meso/rac = 11:1), we were unable to fully separate it from its rac diastereomer using column chromatography or fractional crystallization. Attempted inversion of a single phosphorus center of pure rac-IsMePCH2PMeIs also failed to produce meso-IsMePCH2PMeIs in a pure form. Chapter 2: Reaction of the bis(phosphine) rac-IsMePCH2PMeIs (Is = 2,4,6-(i-Pr)3C6H2) with two equiv of CuI gave the complex Cu4I4(rac-IsMePCH2PMeIs)2 as a mixture of two diastereomers. The crystal structure of Cu4I4(rac-IsMePCH2PMeIs)2·4CHCl3 showed it adopted a distorted "octahedral" geometry with a rectangular Cu4 plane, two asymmetrically bridging [mu]4-iodides, two [mu]2-iodides and two bis(phosphines) bridging two copper atoms. On UV excitation in the solid state, the cluster Cu4I4(rac-IsMePCH2PMeIs)2 showed temperature-dependent emission from 3XLCT (halide-to-ligand charge transfer) and 3CC (Cu4I4 cluster-centered) excited states. Chapter 3: Kagan's method for obtaining selectivity information from racemic catalysts was applied to the Pt-catalyzed asymmetric benzylation of secondary bis(phosphines) and also expanded to account for cases of substrate control and substrate dissociation. The catalysts Pt(([[plus-minus sign])-BenzP*)(Ph)(Cl) and Pt((R,R)-BenzP*)(Ph)(Cl) were synthesized and screened in a set of reactions with the substrate PhHP(CH2)3PHPh, a variety of benzyl halides (Y[subscript n]C6H5-[subscript n])CH2X (Y = alkyl, -OMe, -Br, -CF3, -F, -CN, -Ph; X = -Cl, -Br), and NaOSiMe3 as a base. C6H5CH2Br was found to be the most selective alkylating agent for this reaction, and the results were compared to those obtained by Brian Anderson using Pt((R,R)-Me-DuPhos)(Ph)(Cl) as catalyst. Pt((R,R)-BenzP*)(Ph)(Cl) (dr = 5.5 [plus-minus sign] 0.5, er = 27 [plus-minus sign] 13 ) was predicted to be a more selective catalyst than Pt((R,R)-Me-DuPhos)(Ph)(Cl), but some substrate dissociation was observed (positive half-alkylation test) due to ligand steric effects, and substrate control with negative cooperativity was detected by comparison with the same reaction utilizing Pt(([plus-minus sign])-BenzP*)(Ph)(Cl) (dr 4.4 [plus-minus sign] 0.4, predicted x = 0.92, er = 120). Lithium-mediated P-phenyl bond cleavage of Ph2PCH2C(CH3)2CH2PPh2 gave the gem-dimethyl secondary bis(phosphine) substrate PhHPCH2C(CH3)2CH2PHPh. Asymmetric alkylation of PhHPCH2C(CH3)2CH2PHPh using the catalysts Pt((±)-BenzP*)(Ph)(Cl) (dr = 2.0, predicted x = 0.80, er = 16) and Pt((R,R)-BenzP*)(Ph)(Cl) (dr = 2.0, er = 2) confirmed that the Thorpe-Ingold effect was successful in preventing substrate dissociation (negative half alkylation test). However, the added steric demand of the two methyl groups exacerbated the negative cooperativity observed previously."

Download or read book Chiral Ferrocenes in Asymmetric Catalysis written by Li-Xin Dai and published by John Wiley & Sons. This book was released on 2010-02-01 with total page 433 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book meets the long-felt need for a reference on ferrocenes with the focus on catalysis. It provides a thorough overview of the synthesis and characterization of different types of chiral ferrocene ligands, their application to various catalytic asymmetric reactions, and versatile chiral materials as well as drug intermediates synthesized from them. Written by the "who's who" of ferrocene catalysis, this is a guide to the design of new ferrocene ligands and synthesis of chiral synthetic intermediates, and will thus be useful for organic, catalytic and synthetic chemists working in academia, industrial research or process development.

Download or read book Comprehensive Asymmetric Catalysis written by Eric N. Jacobsen and published by Springer Science & Business Media. This book was released on 2004-04-21 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: The second supplement to the three volume reference work Comprehensive Asymmetric Catalysis critically reviews new developments to the hottest topics in the field written by recognised experts. Seven chapters which are already in the major reference work have been supplemented and additionally a new chapter on Aminohydroxylation of Carbon-Carbon Double Bonds has been included. Thus, the state of the art in this area is now re-established. Together with the basic three volume book set and Supplement 1 it is not only the principal reference source for synthetic organic chemists, but also for all scientific researchers who use chiral compounds in their work (for example, in biochemical investigations and molecular medicine) as well as for pharmaceutical chemists and other industrial researchers who prepare chiral compounds.

Download or read book Design and Synthesis of Tris heteroleptic Bis cyclometalated Chiral at rhodium Catalysts for Application in Asymmetric Catalysis written by Yvonne Grell and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chiral Sulfur Ligands written by Helene Pellissier and published by Royal Society of Chemistry. This book was released on 2009-10-31 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of this book is to show the high potential of chiral sulfur-containing ligands to promote numerous asymmetric catalytic transformations. The important number of reports appeared in the literature over the last 35 years often highlighted spectacular results in terms of efficiency and enantioselectivity, allowing access to many biologically important molecules, which clearly demonstrates that these ligands can now be recognised as real competitors to the more usual phosphorus- or nitrogen-containing ligands. A key point of reference for post-graduate students, researchers and academics.

Download or read book Chemtracts written by and published by . This book was released on 1998 with total page 596 pages. Available in PDF, EPUB and Kindle. Book excerpt: Consists of reviews, condensations, and commentaries.

Download or read book Abstracts of Papers written by American Chemical Society and published by . This book was released on 1991 with total page 890 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Middle Molecular Strategy written by Koichi Fukase and published by Springer Nature. This book was released on 2021-07-13 with total page 357 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights recently discovered aspects of “middle-size molecules,” focusing on (1) their unique bio-functions on the basis of derivatives and conjugates of natural products, saccharides, peptides, and nucleotides; (2) the synthesis of structurally complex natural products; (3) special synthetic methods for π-conjugated functional molecules; and (4) novel synthetic methods using flow chemistry. Given its scope, the book is of interest to industrial researchers and graduate students in the fields of organic chemistry, medicinal chemistry, and materials science.

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 Synthesis of Chiral Nonracemic C2 symmetric 2 2 bipyridines and Their Evaluation as Ligands in Copper catalyzed Asymmetric Reactions written by Brendan John Whelan and published by . This book was released on 2010 with total page 528 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis concerns the synthesis and evaluation of a series of new chiral nonracemic C2-symmetric 2,2'-bipyridines for use as ligands in catalytic asymmetric reactions. The 2,2'-bipyridines were prepared using a divergent synthetic strategy which employed an asymmetric dihydroxylation reaction of a 2-chloropyrindine as the key step. The resultant chiral diol was condensed with a series of symmetrical ketones to afford chiral acetals which were converted into the requisite ligand series. These ligands were evaluated in the asymmetric copper(I)-catalyzed cyclopropanation reaction of styrene and ethyldiazoacetate. The major Trans-cyclopropane products were isolated in good yield and very high enantioselectivities were achieved (up to 94% ee). These are amongst the highest enantioselectivities reported for chiral 2,2'-bipyridyl ligands. The most effective ligand, an adamantanone derivative, was evaluated in the copper(I)-catalyzed asymmetric allylic oxidation of cyclic alkenes with Tert-butyl peroxybenzoate. High enantioselectivities were also obtained in these reactions (up to 91% ee).

Download or read book Artificial Metalloenzymes and MetalloDNAzymes in Catalysis written by Montserrat Diéguez and published by John Wiley & Sons. This book was released on 2018-02-21 with total page 431 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Part I Novel C2 Symmetric Chiral Lewis Acid Catalysts Based Upon a Camphor Lactam Template for Catalytic Asymmetric Cycloaddition Reactions written by Jing Zhang and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Asymmetric Synthesis of C2 symmetric Bimorpholines and Their Application as Chiral Ligands in the Transfer Hydrogenation of Aromatic Ketones written by Kadri Kriis and published by . This book was released on 2003 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Progress in Heterocyclic Chemistry written by Gordon W. Gribble and published by Elsevier. This book was released on 2009 with total page 584 pages. Available in PDF, EPUB and Kindle. Book excerpt: Progress in Heterocyclic Chemistry (PHC), is an annual review series commissioned by the International Society of Heterocyclic Chemistry (ISHC). Volumes in the series contain both highlights of the previous year's literature on heterocyclic chemistry and articles on new developing topics of particular interest to heterocyclic chemists. The highlight chapters in Volume 21 are all written by leading researchers in their field and these chapters constitute a systematic survey of the important original material reported in the literature of heterocyclic chemistry in 2008. Additional articles in this volume review 'Biocatalytic approaches to chiral heterocycles' and 'Ring-expanded ('fat') purines and their nucleoside/nucleotide analogues as broad-spectrum therapeutics'. As with previous volumes in the series, Volume 21 will enable academic and industrial chemists, and advanced students, to keep abreast of developments in heterocyclic chemistry in a convenient way. CONTENTS Biocatalytic approaches to chiral heterocycles (Steven J. Collier, Michael A. K. Vogel, Brian J. Wong and Naga K. Modukuru); Ring-expanded ('fat') purines and their nucleoside/nucleotide analogues as broad-spectrum therapeutics (Ramachandra S. Hosmane); Three-membered ring systems (Stephen C. Bergmeier and David J. Lapinsky); Four-membered ring systems (Benito Alcaide and Pedro Almendros); Five-membered ring systems: Thiophenes and Se/Te analogues (Tomasz Janosik and Jan Bergman); pyrroles and benzo analogs (Jonathon S. Russel, Erin T. Pelkey and Sarah J. P. Yoon-Miller); Furans and benzofurans (Xue-Long Hou, Zhen Yang, Kap-Sun Yeung, Henry N.C. Wong); With more than one N atom (Larry Yet); With N and S (Se) atoms (Yong-Jin Wu and Bingwei V. Yang); With O & S (Se, Te) atoms (R. Alan Aitken); With O & N atoms (Stefano Cicchi, Franca M. Cordero, Donatella Giomi); Six-membered ring systems: Pyridine and benzo derivatives (Darrin W. Hopper, Aimee L. Crombie, and Jeremy J. Clemens, and Soojin Kwon); Diazines and benzo derivatives (Amelia Manlove and Michael P. Groziak); Triazines, tetrazines and fused ring polyaza systems (2007) (Dmitry N. Kozhevnikov and Valery N. Kozhevnikov); Triazines, tetrazines and fused ring polyaza systems (2008) (Dmitry N. Kozhevnikov and Valery N. Kozhevnikov); Six-membered ring systems: With O and/or S atoms (John D. Hepworth and B. Mark Heron); Seven-membered rings (Jason A. Smith, Peter P. Molesworth and John H. Ryan); Eight-membered and larger rings (George R. Newkome); Index.