<<

Stereochemistry11 in Organic

Dr Jyotsna Meshram Reader Postgraduate Department of Chemistry Nagpur University Nagpur (M.S.), India

DATTSONS

NAGPUR Contents

Preface v

1 Contributions to Chemistry 1 # August Kekule

# Jacobus Henricus Vant's Hoff

#

# # Sir # #

# Sir

# Sir

1.1 Some useful terms in 3 1.2 Introduction 7

1.3 Isomers 9

1.3 A Constitutional isomers and stereoisomers 10 1.3B Configurational and conformational isomers 11 1.3C Geometrical and optical isomers 12 1.4 Conformational analysis 17 1.4A Conformational analysis of 18 1.4B Conformational analysis of cycloalkanes 25 1.4B1 Conformational analysis of cyclopropane 28 1.4B2 Conformational analysis of cyclobutane 29 viii

1.4B3 Conformational analysis of eyelopentane 29 1.4B4 Conformational analysis of cyclohexane 30 1.4B5 Conformational analysis of bicyclohexane (Decalins) 35

1.5 Conformation of sugars 37 1.5A Monosaccharides 37

1.5B Disaccharides 45

1.5C Mutorotation 45

1.6 Effect of substitution and Steric strain due to unavoidable crowding 48 1.6 A. Effect of substitution 48

1.6B Stereochemistry of alkaloids 50 1.6C Stereochemistry of 51 1.6D Stereochemistry of terpenoids 52 1.6E Steric strain due to unavoidable crowding in other organic compounds 53 1.6F Catenanes and rotaxanes 54 1.6G Strained Hydrocarbons 55 1.7 Elements of symmetry 55 1.7 A Plane of symmetry/ mirror plane 5 5

1.7B Center of symmetry/point of symmetry 56 1.8 Chirality 57

1.9 (R - S) system of nomenclature of enantiomers 58

2 Optical Activity 61 2.1 Specific rotation 63 2.2 Optical purity 64

2.3 Molecules with one chiral center 65

2.4 Molecules with more than one chiral centre 66

2.4A Enantiomers and distereomers 68

2.4B Threo and erythro isomers 73 2.4C Meso compounds 74 2.5 Molecules with multiple chiral centers 76 2.6 Racemic modifications 77 ix

2.7 Methods of resolution 79 2.7A Mechanical separation 79 2.7B Resolution by micro- organisms 80 2.7C Chromatography 80 2.7D Chemical conversion of a pair of enantiomers into a pair of distereorners 81

2.7E Kinetic resolution 84

2.8 Enantiotopic and disterotopic atoms, Groups and faces 84 2.9 Sterteochemistry of organic reactions 88 Regioselective, steroselective and sterospecific reactions 2.9A Hydrobromination 90 2.9B Hydroboration 94 2.9C bromination 97

2.9D Oxymercuration of 99 2.9E Glycol formation 100 2.9F Catalytic hydrogenation 102 2.9G Elimination reaction 104 2.9H Nucleophilic substitution 106

3 Asymmetric Synthesis 109 3 .OA Substrate controlled methods 110

3.0B Auxiliary controlled methods 110 3.0C Reagent controlled methods 111 3.0D Catalyst controlled methods 111 3.1 Optical activity in the absence of chiral (Biphenyls, Allenes and Spiranes) 113 3.1A Optical activity in Allenes 114 3.1B Optical activity in Biphenyls 115 3.1C Optical activity in Spiranes 117 3.2 Stereochemistry of compounds containing , sulfur and phosphorous 118 3.3 Chirality in 119

3.4 Chirality in pharmaceutical s 121 X

3.4A Ibuprofen 122 3.4B Warfarin 122

3.4C Penicillamine 123 3.4D Methyldopa 123 3.4E Naproxen 123 3.4F Thyroxine 123 3.4G Thalidomide 124 3.4H Captopril 124 3.41 Davron and Novrad 125 3.4J Dopa 125 3.4K Ethambutal 125 4 Optical rotatory dispersion 126 4.1 A Introduction 126 4.1B Applications of ORD 130

Bibliography 142

Index 155