Design and Synthesis of Electronically and Sterically Variable Chiral Cyclopentadienyl Transition Metal Complexes and Their Application in Asymmetric Transformations PDF Download
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Author: Timothy Michael Ramsey
Publisher:
ISBN:
Category : Asymmetric analysis
Languages : en
Pages : 498
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Author: Timothy Michael Ramsey
Publisher:
ISBN:
Category : Asymmetric analysis
Languages : en
Pages : 498
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Author: Ronald Lee Halterman
Publisher:
ISBN:
Category :
Languages : en
Pages : 486
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Author: Daniel Christopher Brookings
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Daniel Christopher Brookings
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author:
Publisher:
ISBN:
Category : Dissertation abstracts
Languages : en
Pages : 704
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Author: Marko Hapke
Publisher: Springer Nature
ISBN: 3031573811
Category :
Languages : en
Pages : 208
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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: Wei Li
Publisher:
ISBN:
Category :
Languages : en
Pages : 233
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Author: Jacek Wojaczynski
Publisher: John Wiley & Sons
ISBN: 3527834192
Category : Science
Languages : en
Pages : 692
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Book Description
Chiral Building Blocks in Asymmetric Synthesis A comprehensive introduction to the important classes of chiral building blocks Chirality — the asymmetric quality found in certain chemical compounds — plays an essential role in our world: chiral compounds can be found in biology, pharmaceutical compounds, agrochemicals, and fragrances. The stereoselective preparation of these complex molecular constructions constitutes a challenge. To this end, modern asymmetric synthesis utilizes a variety of valuable and efficient reagents employed as chiral auxiliaries, metal complexes and organocatalysts in stereoselective catalysis, and enantiopure reactants termed as chiral building blocks. In Chiral Building Blocks in Asymmetric Synthesis, the achievements in the fields of preparation of and applications of chiral blocks are presented. In doing so, the book comprehensively discusses the important classes of these reactants as the key for the asymmetric synthesis of chiral molecules. As such, it is an indispensable resource about synthetic methods, as well as possible modifications and transformations of important classes of chiral compounds. It also highlights the importance of their use as reactants and auxiliaries in the preparation of more sophisticated molecules or supramolecular systems. In Chiral Building Blocks in Asymmetric Synthesis readers will also find: Organization according to the most important compound classes — e.g. amino acids, BINOL and its derivatives, terpenes, and others — with an emphasis on synthesis and application A focus on the use of chiral building blocks for the preparation of bioactive compounds and supramolecular assemblies Chiral Building Blocks in Asymmetric Synthesis is a useful reference for organic chemists, catalytic chemists, chemists in industry, medicinal chemists, pharmaceutical chemists, and the libraries that support them.
Author: Daniel Sole
Publisher: Academic Press
ISBN: 0128116528
Category : Science
Languages : en
Pages : 368
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Book Description
Advances in Transition-Metal Mediated Heterocyclic Synthesis provides an overview of recent catalytic reactions involving transition metals to produce heterocyclic compounds. The book is organized according to the type of transformation used to achieve the synthesis of the heterocyclic systems (mainly aza- and oxa-heterocycles). As such, it covers recent applications on the synthesis of heterocycles, also describing the details of the novel transformations in a didactic manner to motivate readers in search of new catalytic processes. The editors have included state-of-the-art strategies, including transition-metal reactions involving unsaturated systems (reactions of allenes, new gold(I)-catalyzed reactions, and Prins reaction). Chapters highlight the versatility of organopalladium chemistry dealing with carbonylative transformations, C-H activation reactions, coupling processes, and the control of the ambiphilic character of organopalladium species. Finally, the book discusses new reactions leading to heterocycles based on C-H activation processes catalyzed by other metals (Rh, Ru, Co). Written by an outstanding team of authors who are leading experts in organometallic chemistry and organic synthesis, this book is a valuable resource not only for chemists mainly focused on synthesis, but also for those interested in reaction mechanisms involving transition metals. - Helpfully organized by transformation type to stimulate the search for new synthetic processes - Completely illustrated and written by global experts - Includes thoughtfully selected strategies chosen by the editors to exemplify the state-of-the-art of the subject, including transition-metal reactions involving unsaturated systems, organopalladium chemistry, and metal-catalyzed C-H activation
