Synthesis and Asymmetric Reactivity of Electronically and Sterically Differentiating Chiral Cyclopentadienyl Metal Complexes PDF Download
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Author: Ronald Lee Halterman
Publisher:
ISBN:
Category :
Languages : en
Pages : 486
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Author: Ronald Lee Halterman
Publisher:
ISBN:
Category :
Languages : en
Pages : 486
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Author: Timothy Michael Ramsey
Publisher:
ISBN:
Category : Asymmetric analysis
Languages : en
Pages : 498
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Author: R.E. Gawley
Publisher: Elsevier
ISBN: 0080514774
Category : Science
Languages : en
Pages : 395
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Book Description
The world is chiral. Most of the molecules in it are chiral, and asymmetric synthesis is an important means by which enantiopure chiral molecules may be obtained for study and sale. Using examples from the literature of asymmetric synthesis (more than 1300 references), the aim of this book is to present a detailed analysis of the factors that govern stereoselectivity in organic reactions. It is important to note that the references were each individually checked by the authors to verify relevance to the topics under discussion. The study of stereoselectivity has evolved from issues of diastereoselectivity, through auxiliary-based methods for the synthesis of enantiomerically pure compounds (diastereoselectivity followed by separation and auxiliary cleavage), to asymmetric catalysis. In the latter instance, enantiomers (not diastereomers) are the products, and highly selective reactions and modern purification techniques allow preparation - in a single step - of chiral substances in 99% ee for many reaction types. After an explanation of the basic physical-organic principles of stereoselectivity, the authors provide a detailed, annotated glossary of stereochemical terms. A chapter on "Analytical Methods" provides a critical overview of the most common methods for analysis of stereoisomers. The authors then follow the 'tried-and-true' format of grouping the material by reaction type. Thus, there are four chapters on carbon-carbon bond forming reactions (enolate alkylations, organometal additions to carbonyls, aldol and Michael reactions, and cycloadditions and rearrangements), one chapter on reductions and hydroborations (carbon-hydrogen bond forming reactions), and one on oxidations (carbon-oxygen and carbon-nitrogen bond forming reactions). Leading references are provided to natural product synthesis that have been accomplished using a given reaction as a key step. In addition to tables of examples that show high selectivity, a transition state analysis is presented to explain - to the current level of understanding - the stereoselectivity of each reaction. In one case (Cram's rule) the evolution of the current theory is detailed from its first tentative (1952) postulate to the current Felkin-Anh-Heathcock formalism. For other reactions, only the currently accepted rationale is presented. Examination of these rationales also exposes the weaknesses of current theories, in that they cannot always explain the experimental observations. These shortcomings provide a challenge for future mechanistic investigations.
Author: Kenichi Endo
Publisher: Springer Nature
ISBN: 9811611637
Category : Science
Languages : en
Pages : 95
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This book describes novel synthetic methodologies for two kinds of structurally elaborate metal complexes: a heterometallic complex and a tetrahedral chiral-at-metal complex. The book provides the tools and inspiration to chemists for development of metal complexes with wide structural diversity than had previously been possible. For each of the two topics, existing synthetic methods for similar compounds are discussed first, and then new strategies are presented, followed by the demonstration of the synthesis of novel compounds supported by experimental results. Both of the final products in this research, a Co–Ni heterometallic complex covered in the first topic and a tetrahedral chiral-at-metal complex in the second one are difficult to obtain by using common synthetic methods for thermodynamic reasons. This research achieved highly selective syntheses of these compounds using newly designed strategies that enable precise kinetic control. Such an approach will be useful for synthesizing other new metal complexes. Since the last century, organic chemistry has flourished with the development of a variety of synthetic techniques that make precise kinetic control possible. Coordination chemistry of 3d or main-group transition metals has been mainly based on simple one-step reactions that yield only thermodynamic products. The publication of this book helps pave the way to kinetically controlled precise syntheses of various metal complexes.
Author: J. Seyden-Penne
Publisher: Wiley-Interscience
ISBN:
Category : Science
Languages : en
Pages : 744
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Book Description
Table of Contents Preface Abbreviations Introduction 1 1 Enantiomerically Pure Chiral Auxiliaries 43 2 Chiral Reagents 87 3 Chiral Catalysis and Catalysts Bearing Chiral Ligands 117 4 Asymmetric Deprotonations and Protonations 143 5 Alkylations and Related Reactions 157 6 Additions to C=O and C=N Double Bonds 209 7 Additions to Carbon-Carbon Double Bonds 367 8 Additions to Double Bonds Bearing Heteroatoms. Oxidations of Sulfides and Selenides 503 9 Cycloadditions 513 10 Sigmatropic Rearrangements 593 11 Transition Metal Catalyzed Reactions 619 References 637 Index 707.
Author: Philip John Davies
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 754
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Author: Michael Christian Ryan
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Using transition metal catalysis to rapidly increase complexity for the construction of small molecules has been one of the most important areas of research in the field of synthetic organic chemistry. In particular, cyclopentadienylruthenium (CpRu) catalysis has previously been shown by our research group and others to be a selective, cost-effective, and atom-economical means of achieving this goal. In an effort to extend CpRu catalysis to enantioselective variants of these reactions, our group had previously developed CpRu complexes containing tethered chiral sulfoxides for their successful application towards asymmetric allylic substitution reactions. This work describes our efforts to expand the chemistry of these CpRu-sulfoxide complexes and to synthesize novel chiral CpRu and indenylruthenium (IndRu) catalysts for the discovery of new catalytic asymmetric cyclization reactions. CpRu-sulfoxide complexes were used to perform an asymmetric redox bicycloisomerization reaction that constructed [3.1.0] and [4.1.0] bicycles from propargyl alcohols. Initial reaction optimization was performed on 1,7-enynes due to the products' similarity to known triple-reuptake inhibitor GSK1360707. CpRu complex containing a tethered para-methoxy sulfoxide ligand proved to be the optimal catalyst for this reaction. Variation of the 1,7-enyne substrate structure revealed that a bulky 2,4,6-triisopropylbenzenesulfonyl (Tris) protecting group on the nitrogen-containing backbone was essential for observing high enantioselectivities for [4.1.0] bicycles. While THF proved to be the optimal solvent for redox isomerization of [4.1.0] bicycles, acetone provided the best results for [3.1.0] bicycles. Enantiomeric ratios as high as 98.5:1.5 were observed with Tris-containing [3.1.0] bicycles. The chemistry could be extended to 1,6-enynes containing other substrate tethers, including tosyl, diphenyl phosphoramidate, and dibenzyl malonate tethers. Nitrogen protecting groups were shown to be removable under reducing conditions. Catalysis performed with enantiomerically enriched propargyl alcohols revealed a matched/mismatched effect that was strongly dependent on the nature of the solvent. To the best of our knowledge, this methodology was the first example of a ruthenium-catalyzed asymmetric cycloisomerization reaction. Unfortunately, CpRu-sulfoxide complexes were shown to be inefficient and poorly selective catalysts for the enyne cycloisomerization and redox isomerization/C-H insertion reactions. We hypothesized that either the bound sulfoxide ligand was too electron-rich or that the catalyst had an insufficient number of coordination sites available for catalysis. In order to test our hypothesis, we synthesized CpRu complexes that contained more electron-withdrawing S-chiral ligands. While chiral sulfimide- and sulfinamide-containing complexes could promote enyne cycloisomerization, these catalysts were poorly enantioselective. These results led us to believe that the ligands were too weakly ligated to the metal center and decomplexed under the reaction conditions. Novel coordinatively unsaturated chiral indenylruthenium complexes with a tethered chiral sulfoxide were designed and synthesized. Enantiomeric ratios of up to 75:25 for enyne cycloisomerization and 84:16 for enyne hydroxycyclization could be obtained using these catalysts. When applied to the asymmetric redox isomerization/C-H insertion reaction, chiral indenylruthenium complexes could promote this reaction in up to 90:10 e.r. The main disadvantage of using these tethered complexes is that they are not commercially available and must be made through multistep syntheses. We discovered that commercially available catalyst CpRu(MeCN)3PF6, when used in conjunction with a chiral phosphoramidite ligand, can perform an asymmetric interrupted metallo-ene reaction of (E)-allylic chlorides in excellent enantioselectivity. To our knowledge, this represents the first example of using CpRu-phosphoramidite complexes for a catalytic asymmetric transformation. The C1-symmetry and 3,3'-substitution on the BINOL-based phosphoramidite were key to the high levels of enantioinduction observed. Carbocyclic and heterocyclic 5- and 6-membered rings could be constructed in> 20:1 d.r. and up to 99:1 e.r. As a demonstration of the utility of this methodology, diastereoselective Friedel-Crafts reactions were performed on the chiral benzylic alcohol products that were observed to proceed with retention of configuration.
Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 858
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Author: Daniel Christopher Brookings
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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