Main description:

Summarizing the emerging field of N-heterocyclic carbenes used in organocatalysis, this is an excellent overview of the synthesis and applications of NHCs focusing on carbon-carbon and carbon-heteroatom bond formation. Alongside comprehensive coverage of the synthesis, characteristics and applications, this handbook and ready reference also includes chapters on NHCs for polymerization reactions and natural product synthesis.

Contents:

Preface xi

Discovery of Catalysis by Nucleophilic Carbenes xiii

About the Editor xvii

1 An Overview of NHCs 1
Matthew N. Hopkinson and Frank Glorius

1.1 General Structure of NHCs 2

1.1.1 Classes of NHCs and Related Stable Carbenes 2

1.1.2 Structural Features Common to All NHCs 4

1.1.3 Stabilization of the Carbene Center 5

1.2 NHCs as -Donating Ligands 7

1.2.1 The Nature of Bonding in NHC Adducts 10

1.2.2 Comparing NHC and Phosphine Ligands 10

1.3 Synthesis of NHCs 11

1.3.1 Generation of the Free Carbene 11

1.3.2 Synthetic Routes Toward Azolium Salt NHC Precursors 12

1.4 Quantifying the Electronic Properties of NHCs 16

1.4.1 pKa Measurements of Azolium Salts 16

1.4.2 Tolman Electronic Parameter (TEP) 17

1.4.3 NMR Measurements 21

1.4.4 Nucleophilicity and Lewis Basicity 24

1.4.5 Electrochemical Methods 24

1.4.6 Computational Methods 25

1.5 Quantifying the Steric Properties of NHCs 26

1.5.1 Percentage Buried Volume (%Vbur) 27

1.5.2 Steric Maps 29

1.6 Concluding Remarks 30

References 30

2 Benzoin Reaction 37
Steven M. Langdon, Karnjit Parmar, Myron M.D.Wilde, and Michel Gravel

2.1 Background and Mechanism 37

2.2 Standard Conditions and Substrate Scope 40

2.3 Enantioselective Homo-benzoin Reactions 41

2.4 Cross-benzoin Reactions 42

2.4.1 Intramolecular Cross-benzoin Reactions 42

2.4.2 Intermolecular Cross-benzoin Reactions 47

2.5 Aza-benzoin Reactions 51

2.5.1 Aza-benzoin Reactions of Aldimines 51

2.5.2 Aza-benzoin Reactions of Ketimines 53

References 54

3 N-Heterocyclic Carbene-catalyzed Stetter Reaction and Related Chemistry 59
Santigopal Mondal, Santhivardhana R. Yetra, and Akkattu T. Biju

3.1 Introduction 59

3.2 Proposed Mechanism of the Stetter Reaction 60

3.3 Intramolecular Stetter Reaction 61

3.4 Intermolecular Stetter Reaction 68

3.5 Cascade Processes Involving Stetter Reaction 79

3.6 NHC-catalyzed Hydroacylation Reactions 82

3.7 Conclusion 89

References 89

4 N-Heterocyclic Carbene (NHC)-Mediated Generation and Reactions of Homoenolates 95
Vijay Nair, Rajeev S. Menon, and Jagadeesh Krishnan

4.1 Homoenolates - An Introduction 95

4.2 N-Heterocyclic Carbenes (NHCs) 97

4.3 NHC-Derived Homoenolates - The Beginning 98

4.4 Mechanistic Pathways Available for NHC-Homoenolates 100

4.5 Reaction of NHC-Homoenolates with Ketones and Ketimines 102

4.6 Reaction of NHC-Homoenolates with Michael Acceptors 108

4.7 -Protonation of Homoenolates and Subsequent Reactions 117

4.8 Homoenolates in Carbon-Nitrogen Bond Formation 122

4.9 Domino Reactions of Homoenolates 124

4.10 New Precursors for Homoenolates 126

4.11 Conclusion 129

References 129

5 Domino Processes in NHC Catalysis 133
Pankaj Chauhan, Suruchi Mahajan, Xiang-Yu Chen, and Dieter Enders

5.1 Introduction 133

5.2 Domino Reactions Involving Homoenolate-Enolate Intermediates 134

5.2.1 Domino Reactions Involving a Michael/Aldol Reaction Sequence 134

5.2.2 Domino Reactions Involving a Michael/Michael Reaction Sequence 138

5.2.3 Domino Reactions Involving a Michael/Mannich Reaction Sequence 140

5.2.4 Domino Reactions Involving a Homo-aldol/Michael Addition Sequence 142

5.3 Domino Reactions Involving Dienolate-Enolate Intermediates 142

5.4 Domino Reactions Involving Unsaturated Acyl Azolium-Enolate Intermediates 145

5.4.1 Domino Reactions Involving a Michael/Aldol Sequence 145

5.4.2 Domino Reactions Involving a Michael/Michael Addition Sequence 149

5.4.3 Domino Reactions Involving a Michael/Mannich Reaction Sequence 152

5.4.4 Domino Reactions Involving a Michael/SN2 Reaction Sequence 153

5.5 Conclusions and Outlook 153

References 154

6 N-Heterocyclic Carbene Catalysis via the