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Microwave Assisted Organic Synthesis

De
296 pages
The first reports on the application of microwaves in organic synthesis date back to 1986, but it was not until the recent introduction of specifically designed and constructed equipment, which countered the safety and reproducibility concerns, that synthetic application of microwaves has become established as a laboratory technique. Microwave assisted synthesis is now being adopted in many industrial and academic laboratories to take advantage of the novel chemistry that can be carried out using a variety of organic reaction types.

This book demonstrates the underlying principles of microwave dielectric heating and, by reference to a range of organic reaction types, it’s effective use in synthetic organic chemistry. To illustrate the impact microwave assisted organic synthesis can have on chemical research, case studies drawn mainly from the pharmaceutical industry are presented.

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Contents
Contributors Preface
1 Theoretical aspects of microwave dielectric heating D. MICHAEL P. MINGOS 1.1 Introduction 1.1.1 Microwave radiation – frequencies available for dielectric heating 1.2 Theoretical basis of dielectric heating 1.2.1 Relaxation times of solvents 1.2.2 Loss tangents 1.3 Dielectric properties of solids 1.4 Comparison of microwave and conventional heating 1.5 Acknowledgement 1.6 References 2 Microwaveaccelerated metal catalysis: organic transformations at warp speed KRISTOFER OLOFSSON and MATS LARHED 2.1 Introduction 2.2 Stille couplings 2.3 Suzuki couplings 2.4 Negishi couplings 2.5 Heck couplings 2.6 Cyanation and Sonogashira reactions 2.7 Carbon–heteroatom coupling reactions 2.8 Asymmetric molybdenumcatalysed allylic alkylations 2.9 Carbonylative couplings 2.9.1 Molybdenum hexacarbonyl as a solid COreleasing reagent 2.9.2 Formamides as liquid COreleasing reagents 2.10 Outlook 2.11 Acknowledgement 2.12 References 3 Heterocyclic chemistry using microwaveassisted approaches THIERRY BESSON and CHRISTOPHER T. BRAIN 3.1 Introduction 3.2 Fivemembered systems with one heteroatom
x xii
1
1
2 4 4 7 14 18 21 21
23
23 24 25 29 29 31 32 34 35 36 38 41 41 41 44
44 45
v
vi
4
3.3
3.4
3.5
3.6
3.7
3.8
3.9 3.10
C ONTENTS
3.2.1 Furans and benzofurans 3.2.2 Pyrroles, indoles and indolizines 3.2.3 Thiophenes Fivemembered systems with two heteroatoms 3.3.1 Imidazoles, pyrazoles and benzimidazoles 3.3.2 Oxazoles, isoxazoles, thiazoles, benzoxazoles and benzothiazoles Fivemembered ring systems with more than two heteroatoms 3.4.1 Triazoles 3.4.2 Oxadiazoles 3.4.3 Tetrazoles Sixmembered heterocycles containing one heteroatom 3.5.1 Pyridines, quinolines, isoquinolines and fused ring analogues 3.5.2 Benzopyrans Sixmembered heterocycles containing at least two heteroatoms 3.6.1 Pyrimidines and quinazolines 3.6.2 Triazines and tetrazines Sevenmembered heterocycles containing at least two heteroatoms: 1,4 and 1,5benzodiazepines Polycyclic heterocycles 3.8.1 Fused ring heterocycles 3.8.2 Fused heterocycles sharing at least one heteroatom Conclusion References
Microwaveassisted reductions TIMOTHY N. DANKS and GABRIELE WAGNER 4.1 Introduction 4.2 Reduction of carbon–carbon multiple bonds 4.2.1 CC multiple bond reduction using transfer hydrogenation 4.2.2 CC multiple bond reduction using other methods 4.3 Reduction of carbonyl groups 4.3.1 Carbonyl reduction using borohydrides 4.3.2 Carbonyl reduction under Meerwein–Ponndorf–Verley conditions 4.3.3 Carbonyl reduction by transfer hydrogenation 4.3.4 Carbonyl reduction by the Cannizzaro reaction 4.3.5 Carbonyl reduction using other methods 4.4 Reduction of nitrogen functional groups 4.4.1 Reduction of imines 4.4.2 Reduction of nitro groups 4.4.3 Reduction of hydrazones and hydrazides
45 46 47 48 48
51
53 53 54 56 57
57 59 61 61 63
63 65 65 68 70 71
75
75 76
76 79 80 81
82 83 84 86 87 87 90 93
5
4.5 4.6 4.7
Hydrodehalogenation Conclusions References
C ONTENTS
Speed and efficiency in the production of diverse structures: microwaveassisted multicomponent reactions JACOB WESTMAN 5.1 Background 5.1.1 Introduction 5.1.2 Designing the method 5.1.3 Benefits with multicomponent reactions 5.1.4 Multicomponent versus onepot synthesis 5.2 Multicomponent reactions 5.2.1 Hantzsch reaction 5.2.2 Biginelli reaction 5.2.3 Ugi reaction 5.2.4 Kindler reaction 5.2.5 Gewald synthesis of 2acyl amino thiophenes 5.2.6 Mannich reaction 5.2.7 Boronic Mannich reaction 5.2.8 Pauson–Khand reaction 5.2.9 Wittig reaction 5.2.10 azaDiels–Alder reaction 5.3 Versatile reagents in multicomponent reactions 5.3.1 (Triphenylphosphoranylidene)ethenone 5.3.2N,NDimethylformamide diethyl acetal 5.3.3N,NDimethylformamide diethyl acetal on solid support 5.4 Miscellaneous products 5.4.1 Imidazoles 5.4.2 Substituted imidazoles 5.4.3 Imidazopyridines 5.4.4 1,2,4Triazine 5.4.5 Indolizines 5.4.6 Substituted pralines 5.4.7 Quinolines 5.4.8 Quinazolin4(3H)ones 5.4.9 Substituted pyrroles 5.4.10 Indoles 5.4.11 Spiroindoles 5.4.12Amino phosphonates 5.4.13 6Cyano5,8dihydropyrido[2,3d]pyrimidin4(3H)ones 5.4.14 Multicomponent reactions using isatoic anhydride 5.4.15 Pyrido[2,3d]pyrimidines 5.5 Summary 5.6 References
vii
95 98 98
102
102 102 102 103 103 105 105 107 107 109 110 111 111 112 112 114 114 114 115 116 117 117 118 119 120 121 122 122 123 124 125 125 126 127 127 128 129 129
viii
6
7
C ONTENTS
Integrating microwaveassisted synthesis and solidsupported reagents IAN R. BAXENDALE, A.L. LEE and STEVEN V. LEY 6.1 Introduction 6.2 Microwave heating of reactions 6.2.1 Heating a heterogeneous sample: polymer considerations 6.2.2 Heating a polymersolvent: a binary phase system 6.2.3 Migration of the reacting species 6.2.4 Reaction heating: solvent considerations 6.3 Microwave reactions with polymersupported reagents 6.3.1 Polymer drying 6.3.2 Reductive aminations 6.3.3 The Henry reaction 6.3.4 Alkylation reactions 6.3.5 OAlkylations of carboxylic acids 6.3.6 Wittig reactions 6.3.7 Acylation reactions 6.3.8 Preparation of isocyanides 6.3.9 Synthesis of thioamides 6.3.10 Esterification of alcohols using heterogeneous acid catalyst 6.3.11 Chemoselective bromomethoxylation 6.3.12 Beckmann rearrangement 6.3.13 Hydrogenation of electrondeficient alkenes 6.3.14 Heck reactions 6.3.15 Ketone–ketone rearrangements using polymersupported AlCl3 6.3.16 Synthesis of 1,3,4oxadiazoles using polymersupported Burgess reagent 6.3.17 Preparation of a substituted 2amino1,3,4oxadiazole library 6.3.18 Synthesis of thiohydantoins 6.3.19 Hydrolysis of sucrose to fructose 6.3.20 Microwavepromoted enzymatic reactions 6.3.21 Spectroscopic estimation of polymersupported functional groups 6.3.22 The synthesis of (+)plicamine 6.3.23 Microwaveassisted scavenging reactions 6.4 Conclusion 6.5 References
Microwaveassisted solidphase synthesis ALEXANDER STADLER and C. OLIVER KAPPE 7.1 Combinatorial chemistry and solidphase organic synthesis 7.2 Microwave chemistry and solidphase organic synthesis 7.2.1 Microwave dielectric heating 7.2.2 Solvents
133
133 134 134 135 138 139 141 142 142 143 143 144 146 147 149 150 152 153 153 155 156
157
157
159 160 161 161
164 164 167 169 170
177
177 178 179 179
8 9
C ONTENTS
7.2.3 Thermal and mechanical stability of polymer supports 7.2.4 Equipment 7.3 Literature survey 7.3.1 Peptide synthesis and related examples 7.3.2 Resin functionalisation 7.3.3 Transitionmetal catalysis 7.3.4 Substitution reactions 7.3.5 Multicomponent chemistry 7.3.6 Condensation reactions 7.3.7 Rearrangements 7.3.8 Cleavage reactions 7.3.9 Miscellaneous 7.3.10 Case study: pyrazinone Diels–Alder chemistry 7.4 Other types of supports 7.5 Conclusion 7.6 References Timesavings associated with microwaveassisted synthesis: a quantitative approach CHRISTOPHER R. SARKO 8.1 Introduction 8.2 Timesavings associated with microwaveassisted synthesis 8.3 Acceleration of combinatorial library design and development stages 8.3.1 The contest 8.3.2 The thermal approach 8.3.3 The microwave approach 8.4 New advances in microwave technology 8.5 References Scaleup of microwaveassisted organic synthesis BRETT A. ROBERTS and CHRISTOPHER R. STRAUSS 9.1 Introduction 9.2 Mechanisms and effects of microwave heating 9.3 Approaches to microwaveassisted organic chemistry 9.3.1 Solventfree methods 9.3.2 Scaleup of solventfree methods 9.3.3 Advantages and disadvantages of solventfree methods 9.3.4 Methods employing solvents 9.3.5 Scaleup of methods employing solvents 9.3.6 Advantages and disadvantages of methods utilising solvents 9.4 Safety 9.5 Tandem technologies involving microwaves 9.6 Concluding remarks 9.7 References
Index
ix
180 183 184 184 188 193 196 201 204 206 208 212 216 218 219 219
222
222 222
224 226 227 229 230 235 237
237 239 242 243 244 247 248 251 259 262 263 265 266
272