Copper-Catalyzed Asymmetric Synthesis E-Book
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- Herausgeber: Wiley-VCH
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
This book reflects the increasing interest among the chemical synthetic community in the area of asymmetric copper-catalyzed reactions, and introduces readers to the latest, most significant developments in the field. The contents are organized according to reaction type and cover mechanistic and spectroscopic aspects as well as applications in the synthesis of natural products. A whole chapter is devoted to understanding how primary organometallics interact with copper to provide selective catalysts for allylic substitution and conjugate addition, both of which are treated in separate chapters. Another is devoted to the variety of substrates and experimental protocols, while an entire chapter covers the use on non-carbon nucleophiles. Other chapters deal with less-known reactions, such as carbometallation or the additions to imines and related systems, while the more established reactions cyclopropanation and aziridination as well as the use of copper (II) Lewis acids are warranted their own special chapters. Two further chapters concern the processes involved, as determined by mechanistic studies. Finally, a whole chapter is devoted to the synthetic applications. This is essential reading for researchers at academic institutions and professionals at pharmaceutical or agrochemical companies.
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Seitenzahl: 598
Veröffentlichungsjahr: 2013
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Table of Contents
Related Titles
Title Page
Copyright
List of Contributors
Introduction
Chapter 1: The Primary Organometallic in Copper-Catalyzed Reactions
1.1 Scope and Introduction
1.2 Terminal Organometallics Sources Available
1.3 Coordination Motifs in Asymmetric Copper Chemistry
1.4 Asymmetric Organolithium–Copper Reagents
1.5 Asymmetric Grignard–Copper Reagents
1.6 Asymmetric Organozinc–Copper Reagents
1.7 Asymmetric Organoboron–Copper Reagents
1.8 Asymmetric Organoaluminium–Copper Reagents
1.9 Asymmetric Silane and Stannane Copper-Promoted Reagents
1.10 Conclusions
References
Chapter 2: Copper-Catalyzed Asymmetric Conjugate Addition
2.1 Introduction
2.2 Conjugate Addition
2.3 Trapping of Enolates
References
Chapter 3: Copper-Catalyzed Asymmetric Conjugate Addition and Allylic Substitution of Organometallic Reagents to Extended Multiple-Bond Systems
3.1 Introduction
3.2 Copper-Catalyzed Asymmetric Conjugate Addition (ACA) to Polyconjugated Michael Acceptors
3.3 Copper-Catalyzed Asymmetric Allylic Substitution on Extended Multiple-Bond Systems
3.4 Conclusion
References
Chapter 4: Asymmetric Allylic Alkylation
4.1 Introduction
4.2 Nucleophiles in Enantioselective Process Development
4.3 Functionalized Substrates
4.4 Desymmetrization of meso-Allylic Substrates
4.5 Kinetic Resolution Processes
4.6 Direct Enantioconvergent Transformation
4.7 Conclusion and Perspectives
References
Chapter 5: Ring Opening of Epoxides and Related Systems
5.1 Introduction
5.2 Copper-Catalyzed Asymmetric Ring Opening of Epoxides with Amines
5.3 Copper-Catalyzed Asymmetric Ring Opening of Epoxides and Aziridines with Organometallic Reagents
5.4 Copper-Catalyzed Asymmetric Ring Opening of Heterobicyclic Systems with Organometallic Reagents
5.5 Conclusions
References
Chapter 6: Carbon–Boron and Carbon–Silicon Bond Formation
6.1 Introduction
6.2 C–B Bond Formation Reactions
6.3 C–Si Bond Formation Reactions
6.4 Summary
References
Chapter 7: CuH in Asymmetric Reductions
7.1 Introduction
7.2 Asymmetric Conjugate Reductions
7.3 Asymmetric 1,2-Additions
7.4 Heterogeneous Catalysis
7.5 Conclusions and Perspective
References
Chapter 8: Asymmetric Cyclopropanation and Aziridination Reactions
8.1 Introduction
8.2 Asymmetric Cyclopropanation
8.3 Asymmetric Aziridination
8.4 Conclusion
References
Chapter 9: Copper-Catalyzed Asymmetric Addition Reaction of Imines
9.1 Introduction
9.2 Copper-Catalyzed Asymmetric Addition Reaction of Dialkylzinc to Imines
9.3 Copper-Catalyzed Asymmetric Allylation, Arylation, and Alkynylation Reactions of Imines
9.4 Copper as a Lewis Acid Catalyst for Asymmetric Reaction of Imines
9.5 Conclusions
References
Chapter 10: Carbometallation Reactions
10.1 Introduction
10.2 Carbometallation of Cyclopropenes
10.3 Carbometallation of Alkynes
10.4 Summary
Acknowledgments
References
Chapter 11: Chiral Copper Lewis Acids in Asymmetric Transformations
11.1 Introduction
11.2 Cycloadditions
11.3 Claisen Rearrangements
11.4 Ene Reactions
11.5 Nucleophilic Addition to C=O and C=N Double Bonds
11.6 Conjugate Additions
11.7 α-Functionalization of Carbonyl Compounds
11.8 Kinetic Resolution
11.9 Asymmetric Desymmetrization
11.10 Free-Radical Reactions
11.11 Conclusions
References
Chapter 12: Mechanistic Aspects of Copper-Catalyzed Reactions
12.1 Introduction
12.2 Conjugate Addition
12.3 Allylic Alkylation and Substitution
12.4 Copper as Lewis Acid
12.5 1,2-Addition to Imines and Carbonyls
12.6 Copper Hydride
12.7 Cyclopropanation, Aziridination, and Allylic Oxidation
References
Chapter 13: NMR Spectroscopic Aspects
13.1 Introduction
13.2 Copper Complexes with Phosphoramidite Ligands
13.3 Copper Complexes with TADDOL-Based Thiolate Ligands
13.4 Copper Complexes with Ferrocenyl-Based Ligands
13.5 Conclusion
Acknowledgment
References
Chapter 14: Applications to the Synthesis of Natural Products
14.1 Introduction
14.2 Copper-Catalyzed Conjugate Additions in Natural Product Synthesis
14.3 Natural Product Synthesis Employing Asymmetric Allylic Alkylation
14.4 Asymmetric Copper-Catalyzed Diels–Alder Reactions
14.5 Asymmetric Copper-Catalyzed Mukaiyama Aldol Reactions
14.6 Other Asymmetric Copper-Catalyzed Aldol-Type Reactions
14.7 Asymmetric 1,3-Dipolar Cycloaddition and Claisen Rearrangement
14.8 Catalytic Asymmetric Cyclopropanation
14.9 Asymmetric Copper-Catalyzed Conjugate Reductions
14.10 Copper-Catalyzed Asymmetric 1,2-Type Addition Reactions
14.11 Miscellaneous Asymmetric Copper-Catalyzed Reactions
14.12 Conclusion
References
Index
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The Editors
Prof. Dr. Alexandre Alexakis
University of Geneva
Dept. of Organic Chemistry
Postfach 30
1211 Genève 4
Switzerland
Prof. Dr. Norbert Krause
University Dortmund
Organic Chemistry II
Otto-Hahn-Str. 6
44227 Dortmund
Germany
Prof. Dr. Simon Woodward
University Of Nottingham
School of Chemistry
University Park
Nottingham NG7 2RD
United Kingdom
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany
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List of Contributors
Introduction
Alexandre Alexakis, Norbert Krause, and Simon Woodward
Copper is a metal of choice in organometallic chemistry. It is also one of the first metals to be extensively used in organic synthesis. Early work in the 1960s focused on reactivity and chemoselectivity with stoichiometric organocopper and cuprate reagents. Over the years, it was realized that copper, as a transition metal, could also be used in catalytic amounts mainly associated with Grignard reagents.
The stereoselectivity aspect has also been addressed quite early, again with stoichiometric reagents. Logically, the next step was to apply these stereoselective processes to asymmetric synthesis, thanks initially to chiral auxiliaries. Excellent methodologies affording highly enantioenriched compounds emerged in the 1970s and 1980s. At the same time, purely enantioselective methods with chiral heterocuprates or ligands could not bring really viable solutions, with the notable exception of cyclopropanation. It has to be emphasized that most authors focused on the most popular reaction, that is, conjugate addition.
One of the problems in organocopper chemistry was the lack of mechanistic knowledge to better apprehend how a ligand could interact with the metal and the substrate. Considerable progress was made in the 1990s, particularly owing to new spectroscopic methods and density functional theory (DFT) calculations. Despite that, the design of chiral ligands remains essentially experimental.
Enantioselective and catalytic organocopper reactions really took off in the late 1990s. New ligands and new types of primary organometallics were introduced that allowed high ee's and high turnovers. Of course these turnovers do not match the levels of asymmetric hydrogenations, but they are quite good for C–C bond formation. Thus, asymmetric conjugate addition and allylic substitution afford, nowadays, excellent enantioselectivities (95–99%), both for tertiary and quaternary centers. Further, the range of substrates is becoming larger and larger, and the number of available chiral ligands is over 600, as disclosed in the last decade! With the development of new methodologies, there is a boom in the applications to synthesis of natural products, showing the increasing interest of the chemical synthetic community. A cursory search of the Scifinder database reveals that the field of enantioselective reactions promoted by copper has maintained remarkable growth in the period 1970–2012, with the number of publications doubling every 5–8 years (Figure 1).
Figure 1 Number of publications containing the keywords ‘enantioselective’ and ‘copper’ in the Scifinder database during the period 1970–2012.
The aim of this book is to capture the essence of this activity and introduce the reader to the variety of solutions for many reaction types involving copper catalysis. For the most popular reactions, conjugate addition and allylic substitution, a primary organometallic is needed. Therefore, a whole chapter is devoted to understand their subtleties and advantages and how they interact with copper salts. Asymmetric conjugate addition is a mature field and a chapter is devoted to the variety of substrates and experimental combinations. Multiunsaturated substrates, which were introduced more recently, add one more variable to the equation, that is, that of regioselectivity. Another chapter is devoted to allylic substitution, a truly fascinating reaction that differs considerably from reactions catalyzed by other transition metals (Pd, Ir, Mo, etc.). The extension of allylic substitution to other types of electrophiles, such as epoxides, is also described in a chapter dedicated to this. Another recent aspect is the use of noncarbon nucleophiles, such as B and Si, and a special chapter is devoted to this aspect. Reductions with intermediate copper hydrides have also been investigated with excellent results. Other chapters deal with less known reactions, such as the carbometallation, the additions to imines, and related systems. Special chapters are devoted to the older successful copper-catalyzed reactions, such as cyclopropanation and aziridination, and the use of copper(II) Lewis acids. In parallel to the synthetic aspects, mechanistic studies shed new light on the processes involved–two chapters concern these aspects. Finally, it should be recalled that all the new methodologies, asymmetric or not, catalytic or stoichiometric, show their true value when applied to total synthesis. This is why a whole chapter is devoted to synthetic applications.
We hope that this book will help the readers in finding their topic of interest and the best way to include this chemistry in their synthetic plans and applications.
Chapter 1
The Primary Organometallic in Copper-Catalyzed Reactions
Simon Woodward
1.1 Scope and Introduction
In this chapter, the term primary organometallic will mean both the terminal organometallic (RM) selected for a desired asymmetric transformation and those Cu-species that result once the RM is combined with a suitable copper precursor. A significant advantage in copper-promoted chemistry is the ability to access a very wide library of M[CuXRLn] species (M, main group metal; X, halide or pseudohalide; R, organofunction; L, neutral ligand) by simple variation of the admixed reaction components. Normally, the derived cuprate mixture is under rapid equilibrium such that if one species demonstrates a significant kinetic advantage, highly selective reactions can be realized. The corollary to this position is that deconvoluting the identity of such a single active species from the inevitable “soups” that result from practical preparative procedures can prove highly challenging. In this review, we concentrate on asymmetric catalytic systems developed in the last 10 years, but where necessary, look at evidence from simpler supporting achiral/racemic cuprates. Our aim is to try and present a general overview of bimetallic (chiral) cuprate structure and reactivity. However, given this extremely wide remit, the coverage herein is necessarily a selective subset from the personal perspective of the author. There are a number of past books of general use (either totally or in part) that provide good primers for this area [1]. Additionally, because of its relevance the reader is advised to also consult Chapter 12, which deals with mechanism.
1.2 Terminal Organometallics Sources Available
Figure 1.1 Approximate relative use (n) of group II–IV organometallics in copper-promoted asymmetric processes, and percentage increase of activity over 2007–mid 2012 (black roundels)1).
The seven metals identified (Li, Mg, Zn, B, Al, Si, and Sn) form the basis of this overview. It should be noted that (i) the dominance of magnesium is due to numerous simple addition reactions where the resultant stereochemistry is controlled only by a chiral substrate; (ii) asymmetric reactions of the organometallics of the lower periods are still largely unreported; (iii) while all areas have developed, there has been especial interest in some metalloids in recent years (e.g., organoboron reactions); and (iv) the use of silicon organometallics is over reported in Figure 1.1 by the extensive use of silanes as reducing agents. The general properties of the organometallics used in asymmetric copper-promoted reactions are given in Table 1.1, compared with a generalized LCuR fragment. A common feature is their tendency to form strong bonds with oxygen, providing strong thermodynamic driving forces for additions to carbonyl-containing substrates. This tendency can be correlated to their relatively low electronegativities and high oxophilicities (“hardness” defined here as E(M − O)/E(M − S)]. The published Sn–O bond energy, derived from density functional theory (DFT) calculation, is probably somewhat underestimated in this respect. The reactivity of main group organometallics in Table 1.1 is reinforced by their weak M–C bonds. In fact, M–Me values are often upper limits – the bond energies of the higher homologs are frequently lower by 5–10 kcal mol meaning that in mixed RMMe the methyls can be used as a potential nontransferable groups. Similarly, significant increases in the reactivity of organoelement compounds across the series M(alkyl), M(aryl), and M(allyl) are observed. At least in the allyl case, this is correlated to the M–C bond strength, which is typically >10 kcal mol lower than M–Me.
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