I. Enantioselective Nickel-catalyzed Reductive Coupling Reactions of Alkynes and Aldehydes PDF Download
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Author: Elizabeth Anne Colby Davie
Publisher:
ISBN:
Category :
Languages : en
Pages : 332
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Book Description
(Cont.) A model for the stereoselectivity observed in the macrocyclizations is also proposed. ... amphidinolide T1 amphidinolide T4 * site of catalytic, stereoselective macrocyclization.
Author: Elizabeth Anne Colby Davie
Publisher:
ISBN:
Category :
Languages : en
Pages : 332
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Book Description
(Cont.) A model for the stereoselectivity observed in the macrocyclizations is also proposed. ... amphidinolide T1 amphidinolide T4 * site of catalytic, stereoselective macrocyclization.
Author: Karen Marie Miller
Publisher:
ISBN:
Category :
Languages : en
Pages : 374
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Book Description
Catalytic addition reactions to alkynes are among the most useful and efficient methods for preparing diverse types of substituted olefins. Controlling both regioselectivity and (EIZ)- selectivity in such transformations presents a significant challenge. In reactions that also involve the creation of a new stereocenter, the development of enantioselective processes is highly desirable. Several novel, nickel-catalyzed carbon-carbon bond-forming reactions of alkynes that display excellent regioselectivity and (E/Z)-selectivity are described. These reactions afford synthetically useful allylic and homoallylic alcohols, often with high enantioselectivity. A highly enantioselective method for the nickel-catalyzed reductive coupling of alkynes and aldehydes has been realized using the commercially available (+)- neomenthyldiphenylphosphine as a chiral ligand. Allylic alcohols are afforded with complete (E/Z)-selectivity, generally>95:5 regioselectivity, and in up to 96% ee. In conjuction with ozonolysis, this process is complementary to existing methods of enantioselective [alpha]-hydroxy ketone synthesis. In alkene-directed, nickel-catalyzed reductive couplings of 1,3-enynes with aldehydes and epoxides, the conjugated alkene dramatically enhances reactivity and uniformly directs regioselectivity, independent of the nature of the other alkyne substituent (aryl, alkyl (1°, 2°, 3°)) or the degree of alkene substitution (mono-, di-, tri-, and tetrasubstituted). The highly substituted 1,3-diene products are useful in organic synthesis and, in conjunction with a Rh-catalyzed, siteselective hydrogenation, afford allylic and homoallylic alcohols that previously could not be prepared in high regioselectivity (or at all) with related Ni-catalyzed alkyne coupling reactions. Enantiomerically enriched terminal epoxides can be employed to afford enantiomerically enriched homoallylic alcohols. P-chiral, monodentate ferrocenyl phosphine ligands are efficient promoters of catalytic, asymmetric reductive coupling reactions of 1,3-enynes with aromatic aldehydes and with ketones. The latter represents the first catalytic intermolecular reductive coupling of alkynes and ketones, asymmetric or otherwise, to be reported. Both of these methods afford chiral 1,3-dienes in excellent regioselectivity and modest enantioselectivity. Nickel-catalyzed reductive couplings of 1,6-enynes and aldehydes also display very high (>95 : 5) regioselectivity. Use of a monodentate phosphine as an additive leads to formation of the opposite regioisomer in equal and opposite selectivity (5:>95). These results provide strong evidence for an interaction between the remote alkene and the metal center during the regioselectivity-determining step.
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: Chudi O. Ndubaku
Publisher:
ISBN:
Category :
Languages : en
Pages : 482
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Book Description
The application of recently developed stereoselective nickel-catalyzed reductive coupling reactions of alkynes and aldehydes to the synthesis of complex natural product targets was explored. The "B-Type" amphidinolides were selected as ideal targets owing to their molecular complexity and the paucity of synthetically viable means for their total construction. The diastereoselective nickel-catalyzed reductive coupling of simple aryl-substituted alkynes and a-oxyaldehydes was developed and applied to the construction of the C15-C26 region of amphidinolide H3. ... Alternatively, the nickel-catalyzed reductive coupling reaction of 1,3-enynes and aldehydes was found to be a very effective way of installing the congested 1,3-diene moiety common to all members of this class of natural products. This methodology was further examined as a fragment coupling strategy for the syntheses of amphidinolides G3 and H4. This allowed for a highly convergent and functional group tolerant assembly of these ... molecules and, to date, stands as the most complicated setting for the application of the catalytic reductive coupling reaction.
Author: Hélène Pellissier
Publisher: Royal Society of Chemistry
ISBN: 1782624252
Category : Science
Languages : en
Pages : 404
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Book Description
Presenting the impressive range of uses that have been found for nickel chiral catalysts, for researchers and industrialists in organic chemistry, synthesis and medicinal chemistry.
Author: Johann Chan
Publisher:
ISBN:
Category :
Languages : en
Pages : 434
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Book Description
I. Nickel-Catalyzed Intermolecular Reductive Coupling of Alkynes and Aldehydes. Alkynes and aldehydes were coupled reductively in a single catalytic reaction to yield di- and trisubstituted allylic alcohols with high stereoselectivity and regioselectivity. In most cases, a 1:1 ratio of alkyne to aldehyde was sufficient for efficient coupling. The yield and regioselectivity were strongly dependent on the phosphine ligand, but the allylic alcohols formed were invariably the products of cis addition to the alkyne. [Image] ... II. Enantioselective Synthesis of ( - )-Terpestacin and Structural Revision of Siccanol Using Catalytic Stereoselective Fragment Couplings and Macrocyclizations. ( - )-Terpestacin (1), (naturally occurring enantiomer) and (+)-1 -epi-terpestacin (2) were prepared using catalyst-controlled, stereoselective intermolecular reductive couplings of alkyne 9 and aldehyde 10. Related to enantioselective methods developed in our laboratory, these stereoselective fragment couplings were instrumental in confirming that "siccanol" is not 11-epi-terpestacin, but in fact is ( - )-terpestacin itself.
Author: Katrina Sue Woodin
Publisher:
ISBN:
Category :
Languages : en
Pages : 157
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Book Description
Catalytic Asymmetric Reductive Coupling of 1,3-Enynes and Aromatic Aldehydes Nickel-catalyzed reductive coupling reactions of 1,3-enynes and aromatic aldehydes efficiently afford conjugated dienols in excellent regioselectivity and modest enantioselectivity. These reactions were conducted in the presence of a catalytic ligand (R)-ferrocenyl(2-isopropylphenyl)phenylphosphine, whose overall synthesis was improved during the course of this investigation. 1-(Trimethylsilyl)-substituted enynes are shown to be efficient coupling partners in these reactions, and the dienol products formed readily undergo protiodesilylation under mild conditions. ... Catalytic, Asymmetric, Intramolecular Reductive Coupling of 1,1-Disubstituted Epoxides and Alkynes: Total Synthesis of Pumiliotoxin 209F and 251D Pumiliotoxins 209F and 251 D were prepared using a novel nickel-catalyzed intramolecular cyclizations between alkynes and 1,1-disubstituted epoxides. These cyclizations formed exclusively endo products without the use of a directing group on the alkyne. The synthesis of the reductive coupling precursors involved a diastereoselective sulfur ylide epoxidation of a proline-derived methyl ketone, where the choice of sulfonium salt conferred a major effect on the diastereoselectivity.
Author: Sensuke Ogoshi
Publisher: John Wiley & Sons
ISBN: 3527344071
Category : Science
Languages : en
Pages : 348
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Book Description
A comprehensive reference to nickel chemistry for every scientist working with organometallic catalysts Written by one of the world?s leading reseachers in the field, Nickel Catalysis in Organic Synthesis presents a comprehensive review of the high potential of modern nickel catalysis and its application in synthesis. Structured in a clear and assessible manner, the book offers a collection of various reaction types, such as cross-coupling reactions, reactions for the activation of unreactive bonds, carbon dioxide fixation, and many more. Nickel has been recognized as one of the most interesting transition metals for homogeneous catalysis. This book offers an overview to the recently developed new ligands, new reaction conditions, and new apparatus to control the reactivity of nickel catalysts, allowing scientists to apply nickel catalysts to a variety of bond-forming reactions. A must-read for anyone working with organometallic compounds and their application in organic synthesis, this important guide: -Reviews the numerous applications of nickel catalysis in synthesis -Explores the use of nickel as a relatively cheap and earth-abundant metal -Examines the versatility of nickel catalysis in reactions like cross-coupling reactions and CH activations -Offers a resource for academics and industry professionals Written for catalytic chemists, organic chemists, inorganic chemists, structural chemists, and chemists in industry, Nickel Catalysis in Organic Synthesis provides a much-needed overview of the most recent developments in modern nickel catalysis and its application in synthesis.
Author: Sanjeewa K. Rodrigo
Publisher:
ISBN:
Category :
Languages : en
Pages : 228
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Book Description
Coupling or cycloaddition of two different p-components for the construction of more complex structural motifs is commonly used in organic synthesis. Most of these systems involve a transition metal based catalyst and for reductive coupling reactions, various reducing agents are also employed. This dissertation is focused on the development and mechanistic investigation of nickel-catalyzed reductive coupling processes for useful organic transformations, specifically the coupling of aldehydes and alkynes and the cyclotrimerization of alkynes.
Author: Ryan Thomas McLeod Moslin
Publisher:
ISBN:
Category :
Languages : en
Pages : 200
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Book Description
Nickel-Catalyzed Reductive Coupling Reactions of Aldehydes and Chiral 1,6-Enynes. A study of nickel-catalyzed reductive coupling reactions of aldehydes and chiral 1,6-enynes has provided evidence for stereospecific ligand substitution from a planar three-coordinate nickel species as a plausible explanation of regioselectivity in the nickel-catalyzed reductive coupling of aldehydes and 1,6-enynes. In the absence of a phosphine additive, high regioselectivity and high diastereoselectivity are obtained as a direct result of coordination of both the alkyne and the olefin to the metal center during the C-C bond-forming step. ... Total Synthesis of (+)-Acutiphycin. Synthetic studies toward the total synthesis of (+)-acutiphycin led to, and were in turn further developed by, the study of nickel-catalyzed reductive coupling reactions of 1,6-enynes and aldehydes. ... Ultimately, though not employing the nickel-catalyzed reaction, a highly convergent total synthesis of (+)-acutiphycin featuring an intermolecular SmI2-mediated Reformatsky coupling reaction and macrolactonization initiated by a retro-ene reaction of an alkoxyalkyne was developed. The resulting synthesis was 18 steps in the longest linear sequence from either methyl acetoacetate or isobutyraldehyde. ...
