[PDF] Chiral Pyridyl Phosphinite Catalysts And The Development Of Structure Selectivity Relationships In The Asymmetric Hydrogenation Of Trisubstituted Alkenes eBook

Author : Qi-Lin Zhou
Publisher : John Wiley & Sons
Page : 670 pages
File Size : 27,96 MB
Release : 2011-02-10
Category : Technology & Engineering
ISBN : 3527635211

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Catalytic asymmetric synthesis has been one of the most active research areas in chemistry (Nobel Prize in 2001). The development of efficient chiral catalysts plays a crucial role in asymmetric catalysis. Although many chiral ligands/catalysts have been developed in the past decades, the most efficient catalysts are derived from a few core structures, called "privileged chiral catalysts". This ultimate "must have" and long awaited reference for every chemist working in the field of asymmetric catalysis starts with the core structure of the catalysts, explaining why a certain ligand or catalyst is so successful. It describes in detail the history, the basic structural characteristics, and the applications of these "privileged catalysts". This novel presentation provides readers with a much deeper insight into the topic and makes it a must-have for organic chemists, catalytic chemists, chemists working with/on organometallics, chemists in industry, and libraries. From the contents: * BINAP * Bisphosphacycles - From DuPhos and BPE to a Diverse Set of Broadly Applied Ligands * Josiphos Ligands: From Discovery to Technical Applications * Chiral Spiro Ligands * Chiral Bisoxazoline Ligands * PHOX Ligands * Chiral Salen Complexes * BINOL * TADDOLate Ligands * Cinchona Alkaloids * Proline Derivatives

Author : Zhiming Xu
Publisher :
Page : 332 pages
File Size : 32,38 MB
Release : 2017
Category :
ISBN :

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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.

Author : Junliang Zhang
Publisher : Elsevier
Page : 322 pages
File Size : 31,90 MB
Release : 2023-05-27
Category : Science
ISBN : 0323852262

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Chiral Phosphorous Based Ligands in Earth-Abundant Transition Metal Catalysis summarizes the most significant progress in the field of chiral phosphine ligand chemistry and a broad range of earth-abundant transition metal/chiral phosphine ligand-catalyzed enantioselective transformations. The book provides an authoritative and in-depth understanding of important topics about asymmetric catalysis based on earth-abundant transition metals/chiral phosphine ligands, making it ideal for organic chemistry researchers working in the field of asymmetric catalysis, synthetic methodologies and total synthesis.The development of new chiral phosphine ligands to achieve precise stereo control in many earth-abundant transition metal-catalyzed reactions is a very important field in organic synthesis, materials science and medicinal chemistry. The asymmetric synthesis promoted by transition metal/chiral phosphine ligands provides one of the most ideal ways to produce valuable optically active chemicals. Includes a discussion of state-of-the-art asymmetric organic reactions mediated by earth-abundant transition metals and chiral phosphine ligands Features the progress and the prospect of chiral phosphine ligands in asymmetric transition metal catalysis Covers the asymmetric reactivity modes of earth-abundant transition metals and phosphine ligands

Author : Christian Ebner
Publisher : Cuvillier Verlag
Page : 262 pages
File Size : 10,54 MB
Release : 2012-03-05
Category : Science
ISBN : 3736940416

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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.

Author : Shinichi Itsuno
Publisher : John Wiley & Sons
Page : 674 pages
File Size : 19,16 MB
Release : 2011-06-28
Category : Technology & Engineering
ISBN : 1118063953

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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.

Author : Li-Xin Dai
Publisher : John Wiley & Sons
Page : 433 pages
File Size : 34,81 MB
Release : 2010-02-01
Category : Science
ISBN : 3527322809

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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.

Author : Iwao Ojima
Publisher : Wiley-VCH
Page : 888 pages
File Size : 22,93 MB
Release : 2000-07-31
Category : Science
ISBN :

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Since this important work was first published in 1993, the field of catalytic asymmetric synthesis has grown explosively, spawning effective new methods for obtaining enantiomerically pure compounds on a large scale and stimulating new applications in diverse fields-from medicine to materials science. Catalytic Asymmetric Synthesis, Second Edition addresses these rapid changes through new or substantially revised contributions from highly recognized world leaders in the field.