Asymmetric Brønsted Acid Catalysis ebook

Table of Contents

Related Titles

Title Page

Copyright

Preface

Chapter 1: Introduction

1.1 Book Structure and Notation

1.2 Catalyst Preparation

1.3 Metal Impurities

References

Chapter 2: Reactions of Imines

2.1 Nucleophilic Addition Reactions

2.2 Mannich Reactions

2.3 Strecker Reactions

2.4 Biginelli Reactions

2.5 Friedel–Crafts Reactions

2.6 Transfer Hydrogenations

2.7 Pericyclic Reactions

2.8 Radical Reactions

References

Chapter 3: Reactions of Generated Imine Intermediates

3.1 Enamines

3.2 Indoles Containing Leaving Groups

3.3

N

-Acetals and Aminals

3.4 Miscellaneous Formation

References

Chapter 4: Reactions of Carbonyls

4.1 Nucleophilic Addition Reactions

4.2 Aldol Reactions

4.3 Pericyclic Reactions

4.4 Reductions

References

Chapter 5: Reactions of Generated Carbonyl Intermediates

5.1 Enol Ethers

5.2 Acetals

5.3 Phenols Containing Leaving Groups

References

Chapter 6: Reactions of Alkenes

6.1 Nucleophilic Addition Reactions

6.2 Friedel–Crafts Reactions

6.3 Pericyclic Reactions

6.4 Cascades

References

Chapter 7: Reactions of Other Substrates

7.1 Aziridines

7.2

O

-Heterocycles and Ethers

7.3 Hydrazines and Hydrazones

7.4 Azo/Diazo Substrates

7.5 Halogens

7.6 Oxidizing Agents

7.7 Miscellaneous Substrates

References

Experimental Protocols

Appendix A: Catalyst Frequency

Appendix B: Overview of Phosphoric Acids (PA)

Appendix C: Overview of

N

-Phosphoramide Acids (NPA)

Appendix D: Overview of SPINOL Phosphoric Acids (SPA)

Appendix E: Overview of All Other Brønsted Acids (BA)

Index

End User License Agreement

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Guide

Table of Contents

Preface

Begin Reading

List of Illustrations

Chapter 1: Introduction

Figure 1.1 Commonly employed catalysts and their notation within this book.

Scheme 1.1 Common synthetic route to BINOL phosphoric acid catalysts.

Chapter 2: Reactions of Imines

Scheme 2.1 Alkylation of α-diazoesters with imines by Terada [1].

Scheme 2.2 Mechanism of diazoester additions to imines [1].

Scheme 2.3 Alkylation of diazoesters with imines by Maruoka [4].

Scheme 2.4 Aziridination with imines by Maruoka [8].

Scheme 2.5 Aziridination with imines by Akiyama [10].

Scheme 2.6 Mechanism of aziridination with imines [8].

Scheme 2.7 Aza-ene reaction by Terada [12].

Scheme 2.8 Mechanism of aza-ene reaction [12].

Scheme 2.9 Allylation of imines by Momiyama and Terada [18].

Scheme 2.10 Allylation of imines by List [19].

Scheme 2.11 Mechanism of allylation of imines [18].

Scheme 2.12 Hydrazone addition to imines by Rueping [20].

Scheme 2.13 Hydrazone addition to imines by Maruoka [21].

Scheme 2.14 Mechanism of hydrazone addition to imines by Rueping [20].

Scheme 2.15 Addition of isocyanides to imines by Wang and Zhu [23].

Scheme 2.16 Mechanism of isocyanide addition to imines [23].

Scheme 2.17 Intermolecular addition of amines to imines by Antilla [30].

Scheme 2.18 Condensation of aldehydes with N-nucleophiles by List [33].

Scheme 2.19 Condensation of aldehydes with N-nucleophiles by Rueping [34].

Scheme 2.20 Mechanism of the condensation reaction.

Scheme 2.21 Addition of alcohols to imines by Antilla [39].

Scheme 2.22 Condensation of aldehydes with N- and O-nucleophiles by List [44].

Scheme 2.23 Kabachnik–Fields reaction by List [46].

Scheme 2.24 Kabachnik–Fields reaction by Bhusare [47].

Scheme 2.25 Mechanism of Kabachnik–Fields reaction [46].

Scheme 2.26 Seminal reports using chiral phosphoric acids for the Mannich reaction by Akiyama [2].

Scheme 2.27 Seminal reports using chiral phosphoric acids for the Mannich reaction by Terada [52].

Scheme 2.28 Mechanism of the Mannich reaction [2].

Figure 2.1 Chiral acid catalysts used for the Mannich reaction.

Scheme 2.29 Vinylogous Mannich reaction by Schneider [65].

Scheme 2.30 Strecker reaction by Rueping [75].

Scheme 2.31 Strecker reaction by Dughera [77].

Scheme 2.32 Mechanism of the Strecker reaction [75].

Scheme 2.33 Strecker-type reaction by Maruoka [81].

Scheme 2.34 Mechanism of the Strecker-type reaction [81].

Scheme 2.35 Biginelli reaction by Gong [82].

Scheme 2.36 Mechanism of the Biginelli reaction [82].

Scheme 2.37 Tuning absolute stereochemistry by catalyst choice by Gong [83].

Scheme 2.38 Friedel–Crafts reaction of indoles with aldimines by You [87].

Scheme 2.39 Mechanism of the Friedel–Crafts reaction [87].

Figure 2.2 Catalysts used for the Friedel–Crafts reaction of aldimines.

Scheme 2.40 Two-step Friedel–Crafts/Michael reaction by Enders [99].

Scheme 2.41 Mechanism of the Friedel–Crafts cascade [99].

Scheme 2.42 Friedel–Crafts reaction of ketimines by Rueping [102].

Scheme 2.43 Friedel–Crafts reaction of ketimines by Wang [106].

Scheme 2.44 Friedel–Crafts reaction of CF

3

-containing ketimines by Bolm [107].

Scheme 2.45 Friedel–Crafts reaction of non-indole aromatics by Terada [109].

Scheme 2.46 Friedel–Crafts reaction of non-indole aromatics by Antilla [110].

Scheme 2.47 Friedel–Crafts reaction of benzenes by Enders [115].

Scheme 2.48 Pictet–Spengler reaction by List [116].

Scheme 2.49 Mechanism of the Pictet–Spengler [116].

Scheme 2.50 Pictet–Spengler reaction to access spiroindolinones by Bernardi and Bencivenni [127].

Scheme 2.51 Pictet–Spengler cascade reaction by Dixon [129].

Scheme 2.52 Transfer hydrogenation of imines by Rueping [133].

Scheme 2.53 Transfer hydrogenation of imines by List [134].

Scheme 2.54 General mechanism of transfer hydrogenation of imines.

Scheme 2.55 Reductive amination by MacMillan [138].

Scheme 2.56 Transfer hydrogenation using a benzothiazoline by Akiyama [142].

Scheme 2.57 Transfer hydrogenation using catecholborane by Enders [149].

Scheme 2.58 Transfer hydrogenation using an indoline by Akiyama [150].

Scheme 2.59 Transfer hydrogenation of α-imino esters by Antilla [152].

Scheme 2.60 Transfer hydrogenation of α-imino esters by Akiyama [155].

Scheme 2.61 Transfer hydrogenation of α-imino esters by Enders [156].

Scheme 2.62 Transfer hydrogenation of 2-substituted quinolines by Rueping [157].

Figure 2.3 New catalysts for quinoline reduction by Betzer and Marinetti [168–170].

Scheme 2.63 Transfer hydrogenation of various

N

-heterocycles by Metallinos [174] and Rueping [175].

Scheme 2.64 The use of low catalyst loadings for transfer hydrogenations by Rueping [177].

Scheme 2.65 Transfer hydrogenation of 2-substituted pyridines by Rueping [179].

Scheme 2.66 Transfer hydrogenation of various

N

-heterocycles by Gong [180] and Rueping [181, 182].

Scheme 2.67 Cascade transfer hydrogenation process by List [183].

Scheme 2.68 Mechanism for cascade transfer hydrogenation process [183].

Scheme 2.69 Cascade hydride transfer-cyclization by Gong [184].

Scheme 2.70 Mechanism for the cascade hydride transfer cyclization [184].

Scheme 2.71 A photocyclization–reduction cascade by Rueping [185].

Scheme 2.72 Mechanism for photocyclization–reduction cascade [185].

Scheme 2.73 Asymmetric protonation triggered by transfer hydrogenation by Rueping [187].

Scheme 2.74 Kinetic resolution of BINAM derivatives by Tian, Liu, and Tan [190].

Scheme 2.75 Aza-Diels–Alder reaction with Brassard's diene by Akiyama [191].

Scheme 2.76 Mechanism of aza-Diels–Alder reaction [191].

Scheme 2.77 Aza-Diels–Alder reaction with a cyclic diene by Rueping [[193]] and Gong [[194]].

Scheme 2.78 Aza-Diels–Alder reaction with enol ethers by Akiyama [196].

Scheme 2.79 Aza-Diels–Alder reaction of imines with enamines by Masson and Zhu [203].

Scheme 2.80 Multicomponent aza-Diels–Alder reaction by Zhu and Sun [214].

Scheme 2.81 Mechanism of multicomponent aza-Diels–Alder reaction [214].

Scheme 2.82 Five-component aza-Diels–Alder type reaction by Lin [215].

Scheme 2.83 Mechanism of five-component aza-Diels–Alder type reaction [215].

Scheme 2.84 1,3-Dipolar cycloaddition of imines with maleates by Gong [217].

Scheme 2.85 Mechanism of 1,3-dipolar cycloaddition [217].

Scheme 2.86 [3+2]-Cycloadditions of hydrazones with alkenes by Rueping [237].

Scheme 2.87 1,3-Dipolar cycloaddition of cyclic azomethine imines by Maruoka [238].

Scheme 2.88 Electrocyclizations of hydrazones by List [241].

Scheme 2.89 Mechanism of electrocyclizations of hydrazones [241].

Scheme 2.90 Electrocyclizations of hydrazones by Rueping [243].

Scheme 2.91 Aza-Cope sigmatropic rearrangement by Rueping [244].

Scheme 2.92 Mechanism of aza-Cope rearrangement [244].

Scheme 2.93 The coupling of radicals with imines by Kim [245].

Chapter 3: Reactions of Generated Imine Intermediates

Scheme 3.1 Self-coupling of enamides by Tsogoeva [1].

Scheme 3.2 Mechanism of self-coupling [1].

Scheme 3.3 Friedel–Crafts reaction of enamides by Terada [3].

Scheme 3.4 Friedel–Crafts reaction of enamides by Zhou [4].

Scheme 3.5 Transfer hydrogenation of enamides by Antilla [7].

Scheme 3.6 Cascade reaction involving a transfer hydrogenation by Rueping [8].

Scheme 3.7 Mechanism of the cascade reaction [8].

Scheme 3.8 Coupling of enamides with 3-hydroxy indoles by Gong [9].

Scheme 3.9 Mechanism of enamide and 3-hydroxy indole couplings [9].

Scheme 3.10 Coupling of ketones by Guo and Peng [11].

Scheme 3.11 Coupling of 2-hydroxy styrenes with 3-hydroxy indoles by Shi [12].

Scheme 3.12 Pinacol rearrangement of 3-hydroxy indoles by Antilla [16].

Scheme 3.13 Mechanism of pinacol rearrangement [16].

Scheme 3.14 Additions to 3-vinyl indoles by Terada [18].

Scheme 3.15 Synthesis of triarylmethanes by You [19].

Scheme 3.16 Synthesis of triarylmethanes by Jiang/Zhang [21].

Scheme 3.17 Mechanism of Friedel–Crafts reaction [19].

Scheme 3.18 Double Friedel–Crafts reaction by You [23].

Scheme 3.19 Mechanism of double Friedel–Crafts reaction [23].

Scheme 3.20 Coupling of enecarbamates with hemiaminal ethers by Terada [25].

Scheme 3.21 Mechanism of enecarbamate couplings with hemiaminal ethers [25].

Scheme 3.22 Aza-Petasis–Ferrier rearrangement by Terada [26].

Scheme 3.23 Mechanism of aza-Petasis–Ferrier rearrangement [26].

Scheme 3.24 Coupling of aminals with β-keto esters by Maruoka [29].

Scheme 3.25 Addition to chiral

N

-acyliminium ions by Rueping [30].

Scheme 3.26 Addition to chiral

N

-acyliminium ions by Lete [31, 32].

Scheme 3.27 Mechanism of addition to chiral

N

-acyliminium ions [30].

Scheme 3.28 Friedel–Crafts reaction of racemic spiroindolinones by You [36].

Scheme 3.29 Mechanism of Friedel–Crafts reaction [36].

Scheme 3.30 Transfer hydrogenation of

N,O

-acetals by Zhou [37].

Scheme 3.31 Activation of enantiotopic C(sp

3

)-hydrogen atoms by Akiyama [40].

Scheme 3.32 Mechanism of hydride shift cyclization [40].

Scheme 3.33 Coupling of α,β-unsaturated lactams with indoles by Huang [41].

Scheme 3.34 Mechanism of coupling of α,β-unsaturated lactams with indoles [41].

Scheme 3.35 Asymmetric cross-dehydrogenative coupling by Toste [42].

Scheme 3.36 Mechanism of cross-dehydrogenative coupling [43].

Chapter 4: Reactions of Carbonyls

Scheme 4.1 Allylboration of aldehydes by Antilla [2].

Scheme 4.2 Allylboration of aldehydes by Hu [3].

Scheme 4.3 Mechanism of allylboration of aldehydes by Goodman and Houk [4, 5].

Scheme 4.4 Propargylation of aldehydes by Antilla [8].

Scheme 4.5 Propargylation of aldehydes by Roush [9].

Scheme 4.6 Carbonyl-ene reaction by Rueping [14].

Scheme 4.7 Hosomi–Sakurai reaction by List [16].

Scheme 4.8 Mechanism of carbonyl-ene reaction [14].

Scheme 4.9 Desymmetrization using a Robinson annulation by Akiyama [17].

Scheme 4.10 Mechanism of desymmetrization [17].

Scheme 4.11 Friedel–Crafts reactions of ketones by Ma [20, 21, 23].

Scheme 4.12 Mechanism of Friedel–Crafts reactions [20, 21, 23].

Scheme 4.13 Intramolecular Schmidt reaction by Zhang [24].

Scheme 4.14 Mechanism of Schmidt reaction [24].

Scheme 4.15 Desymmetrization by List [26].

Scheme 4.16 Desymmetrization by Zhu [27].

Scheme 4.17 Mechanism of desymmetrization [27].

Scheme 4.18 Kinetic resolution of secondary alcohols by Yamada and Takasu [28].

Scheme 4.19 Mechanism of kinetic resolution [28].

Scheme 4.20 Baeyer–Villiger reaction by Ding [33].

Scheme 4.21 Mechanism of Baeyer–Villiger reaction [33].

Scheme 4.22 Acetalization of aldehydes by List [36].

Scheme 4.23 Mechanism of acetalization [36].

Scheme 4.24 Abramov reaction by List [37].

Scheme 4.25 Mukaiyama aldol reaction by List [38].

Scheme 4.26 Mukaiyama aldol reaction by Yamamoto [40].

Scheme 4.27 Mechanism of Mukaiyama aldol reaction [38].

Scheme 4.28 Aldol reaction by Blanchet [41].

Scheme 4.29 Proposed mechanism of aldol reaction by Blanchet [41].

Scheme 4.30 Hetero Diels–Alder by Terada [43].

Scheme 4.31 Hetero Diels–Alder by List [44].

Scheme 4.32 Mechanism of hetero Diels–Alder reaction [43].

Scheme 4.33 Nazarov cyclizations by Rueping [46].

Scheme 4.34 Nazarov cyclizations by Tius [50].

Scheme 4.35 Mechanism of Nazarov cyclization [46].

Scheme 4.36 Reduction of ketones by Antilla [51].

Scheme 4.37 Mechanism of reduction of ketones [51].

Chapter 5: Reactions of Generated Carbonyl Intermediates

Scheme 5.1 Enantioselective protonations by Yamamoto [1].

Scheme 5.2 Enantioselective protonations by Ooi [2].

Scheme 5.3 Mechanism of protonations [1].

Scheme 5.4 Spiroacetalization using a C

2

-symmetric catalyst by List [3].

Scheme 5.5 Mechanism of spiroacetalization [3].

Scheme 5.6 Aldol-type reaction by Terada [6].

Scheme 5.7 Mechanism of aldol-type reaction [6].

Scheme 5.8 Transacetalization by List [7, 8].

Scheme 5.9 Proposed transition states for transacetalization [7, 8].

Scheme 5.10 Hydrogenation of pyrylium ions by Rueping [10].

Scheme 5.11 Hydrogenation of pyrylium ions by Terada [11].

Scheme 5.12 Desymmetrization of diols by Zheng [12].

Scheme 5.13 Addition of indoles to

ortho

-hydroxybenzylic alcohols by Bach [13].

Scheme 5.14 Mechanism of indole addition to

ortho

-hydroxybenzylic alcohols [13].

Scheme 5.15 Synthesis of substituted tetrahydroxanthene by Rueping [14].

Scheme 5.16 Synthesis of substituted tetrahydroxanthene by Schneider [15].

Scheme 5.17 Mechanism of

ortho

-quinone methide reactions [14].

Scheme 5.18 Total synthesis (+)-sacidumlignan D by Hong [18].

Chapter 6: Reactions of Alkenes

Scheme 6.1 Hydroamination by Ackermann [3].

Scheme 6.2 Mechanism of hydroamination [3].

Scheme 6.3 Hydroamination by Toste [4].

Scheme 6.4 Mechanism of hydroamination [4].

Scheme 6.5 Addition of arylamines to nitroolefins by Ooi [6].

Scheme 6.6 Activation of quinone imine ketals by Maruoka [8].

Scheme 6.7 Activation of quinone imine ketals.

Scheme 6.8 Aza-Michael reaction of indoles by You [10].

Scheme 6.9 Contact ion pair allylic substitution by Rueping [15].

Scheme 6.10 Mechanism of contact ion pair allylic substitution [15].

Scheme 6.11 Kinetic resolution of carboxylic acids by Ishihara [18].

Scheme 6.12 Friedel–Crafts reaction of nitroalkenes by Akiyama [19].

Scheme 6.13 Mechanism of Friedel–Crafts reaction [19].

Scheme 6.14 Coupling of β,γ-unsaturated α-keto esters with indoles by Rueping [23].

Scheme 6.15 Coupling of β,γ-unsaturated α-keto esters with indoles by Toy [24].

Scheme 6.16 Coupling of nitroalkenes with pyrroles by You [33].

Scheme 6.17 Coupling of nitroalkenes with 4,7-dihydroindoles by You [34].

Scheme 6.18 Diels–Alder reaction by Yamamoto [36].

Scheme 6.19 Diels–Alder reaction by Terada [38].

Scheme 6.20 Mechanism of Diels–Alder reaction [36].

Scheme 6.21 [3+2] coupling of indoles with quinone monoimines by Zhang [40].

Scheme 6.22 Mechanism of [3+2] coupling of indoles [40].

Scheme 6.23 Cascade process in the synthesis of (−)-debromoflustramine B by Antilla [42].

Scheme 6.24 Mechanism of cascade process [42].

Scheme 6.25 Synthesis of 4a-

epi

-ugonstilbene by Ishihara [44].

Chapter 7: Reactions of Other Substrates

Scheme 7.1 Coupling of

meso

-aziridines with TMS-N

3

by Antilla [1].

Scheme 7.2 Mechanism of

meso

-aziridines opening [1].

Scheme 7.3 Coupling of thiol- and selenium-derived nucleophiles with

meso

-aziridines by Antilla [3] and Sala [4].

Scheme 7.4 Desymmetrization of

meso

-epoxides by Sun [6].

Scheme 7.5 Desymmetrization of oxetanes by Sun [9].

Scheme 7.6 Mechanism of desymmetrization of oxetanes [9].

Scheme 7.7 Rearrangement of racemic epoxides by Du [11].

Scheme 7.8 Resolution with S

N

2-type O-alkylations by List [12].

Scheme 7.9 Resolution with S

N

2-type O-alkylations by List [12].

Scheme 7.10 Fischer indole reaction by List [13].

Scheme 7.11 Mechanism of Fischer indole reaction [13].

Scheme 7.12 Benzidine rearrangement by Kürti [16].

Scheme 7.13 Benzidine rearrangement by and List [17].

Scheme 7.14 Mechanism of benzidine rearrangement [17].

Scheme 7.15 Amination of tryptamines by Antilla [18].

Scheme 7.16 Mechanism of amination [18].

Scheme 7.17 Semi-pinacol rearrangements by Maruoka [23].

Scheme 7.18 Mechanism of semi-pinacol rearrangements [23].

Scheme 7.19 Double addition to nitrodiazoesters by Mattson [24] .

Scheme 7.20 Mechanism of double addition to nitrodiazoesters [24].

Scheme 7.21 Electrophilic fluorination using phase-transfer catalyst by Toste [25].

Scheme 7.22 Mechanism of phase-transfer catalysis [25].

Scheme 7.23 Fluorination of enamides by Toste [30].

Scheme 7.24 Fluoroamination using phase-transfer catalyst by Toste [32].

Scheme 7.25 Fluorination-induced Wagner–Meerwein rearrangement by Alexakis [35].

Scheme 7.26 Mechanism of Wagner–Meerwein rearrangement [35].

Scheme 7.27 Kinetic resolution of bi-aryls by Akiyama [39].

Scheme 7.28 Mechanism of kinetic resolution [40].

Scheme 7.29 Bromocyclization using alkenes by Shi [42].

Scheme 7.30 Mechanism of bromocyclization [42].

Scheme 7.31 Intermolecular bromoesterification by Zhang and Tang [47].

Scheme 7.32 Mechanism of bromoesterification [47].

Scheme 7.33 α-oxygenation by Yamamoto [48].

Scheme 7.34 α-oxygenation by Zhong [50].

Scheme 7.35 Mechanism of α-oxygenation [48].

Scheme 7.36 Sulfoxidation by List [52].

Scheme 7.37 Protonation of ketene dithioacetals by List [54].

Scheme 7.38 Protonation of silyl ketene imines by List [55].

Scheme 7.39 Mechanism of protonation of silyl ketene imines [55].

Scheme 7.40 1,3-Dipolar cycloaddition of nitrones by Yamamoto [56].

Scheme 7.41 Mechanism of 1,3-dipolar cycloaddition [56].

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Asymmetric Brønsted Acid Catalysis

Authors

Prof. Dr. Magnus Rueping

RWTH Aachen University

Institute of Organic Chemistry

Landoltweg 1

52074 Aachen

Germany

Dr. Dixit Parmar

RWTH Aachen University

Institute of Organic Chemistry

Landoltweg 1

52074 Aachen

Germany

Dr. Erli Sugiono

RWTH Aachen University

Institute of Organic Chemistry

Landoltweg 1

52074 Aachen

Germany

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Preface

Asymmetric Brønsted acid catalysis can be considered as one of the fundamental pillars of organocatalysis. Over the course of the last 10 years, it has become one of the most hotly researched fields in modern organic chemistry. Unlike certain fads in chemistry, which seem to gather fame as fast as they lose it, chiral Brønsted acids appear to be well equipped to withstand fashion trends and now hold a permanent position inside synthetic organic toolboxes. Since appearing on the scene in 2004, the number of published reports in this area has been steadily increasing and the last 5 years have seen over 100 publications per year.

These figures in fact can also be considered a little on the conservative side, since they do not include any research where Brønsted acids have been combined with metals or other catalysts, which would add to this number indefinitely. Since acid catalysis is perhaps one of the oldest forms of catalysis known and encompasses a wide spectrum of transformations, chiral Brønsted acids have found plentiful scope to feed upon. However, the catalysts over time have evolved as chemistry has progressed, and nowadays, they function as much more than a source of acidity, for example, they have been employed as chiral counterions, ligands, and phase-transfer agents, to name just a few. In addition, they also possess the ability to work in various mechanistic modes, which has added to their appeal and utility.

Current published literature generally focuses on the field of asymmetric organocatalysis, but this term encompasses such a variety of catalysts, mechanisms, and transformations, which usually forces the coverage to only realistically provide an overview of the surface of Brønsted acid catalysis. As part of our involvement in the field of asymmetric Brønsted acid catalysis, we have been monitoring and accumulating a vast number of publications within this area for the last 10 years. Given the scale of developments that have occurred, we sought it suitable to attempt to collate this wealth of information into a more manageable source of literature. This book therefore should serve as a timely essential to both novices and experts in the field. Furthermore, what differentiates this book over most review articles is that it will be structured primarily by structural motif and secondly by transformations. In doing so, the reader will be more aware of the chemical space that Brønsted acids occupy rather than an exhaustive list of reactions. We hope this book draws curiosity from all corners of organic chemistry, and we envision that it will be a platform for the development of future exciting research within the field, which is we look forward to see.

Aachen, Germany

Magnus Rueping, Dixit Parmar, Erli Sugiono

Chapter 1Introduction

1.1 Book Structure and Notation

The field of asymmetric Brønsted acid catalysis is known to contain a diverse array of catalyst architectures, but by far the most dominant within these are BINOL-derived acids [1–11]. They have become so strongly associated with the term asymmetric Brønsted acid that it is not unusual to see this key descriptor omitted in abstracts of recent literature. To complicate the definition, several classes of hydrogen-bond donors such as BINOLs are sometimes referred to as Brønsted acids