Table Of ContentReactivity and Structure
Concept in Organic Chemistry
Volume 32
Editors
Klaus Hafner Jean-Marie Lehn
Charles W. Rees P. von Rague Schleyer
Barry M. Trost Rudolf Zahradnik
Springer
Berlin
Heide1berg
NewYork
Barcelona
Budapest
Hong Kong
London
Milan
Paris
Tokyo
Donald S. Matteson
Stereodireeted
Synthesis
with Organoboranes
With 14 Tables
t
Springer
Prof. Dr. Donald S. Matteson
Washington State University
Department of Chemistry
Pullman, W A 99164-4630
USA
ISBN-13: 978-3-642-79711-8 e-ISBN-13: 978-3-642-79709-5
DOr: 10.1007/978-3-642-79709-5
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Contents
1 Introduction to Borane Chemistry ............ ............ ....................... ........... 1
1.1 Beginnings .......................................................................................... 1
1.2 Structure and Bonding in Organoboranes .. ...... ...... ............ .......... ....... 2
1.2.1 General Characteristics of Boranes . ...... ...... ....... ..... ........... ..... 2
1.2.2 Size. ........................ ...... ........... ........ .... ........ ........................ .... 2
1.2.3 Bond Strengths ...... .... ........ ........ ...... ...... ......... ......... ..... ........... 4
1.3 General Chemical Properties of Organoboranes. ...... ....... ... ................ 7
1.3.1 Oxidation States of Boron ....................................................... 7
1.3.2 Ligand Exchange on Boron ..................................................... 10
1.3.3 Acidities ................................................................................... 13
1.4 Safety Considerations ......................................................................... 15
1.4.1 General Hazards ...................................................................... 15
1.4.2 Laboratory Handling ........ ........... ...... ...... ...... ............ ....... ........ 17
1.5 References........................................................................................... 18
2 Sources of Compounds Containing Boron-Carbon Bonds ................. 21
2.1 Industrial Sources ofBoron Compounds ............................................ 21
2.2 The Organometallic Route .................................................................. 21
2.2.1 Boronic Esters.. ... .............. ...... ... ...... ...... ...... ................ ..... ... .... 21
2.2.1.1 Grignard and Lithium Reagents ................................. 21
2.2.1.2 Other Organometallics .......... ........ .............. ..... ...... .... 24
2.2.2 Di-, Tri-, and Tetraborylmethanes ........................................... 25
2.2.3 Borinic Esters (Dialkylalkoxyboranes) ................................... 25
2.2.4 Trialkylboranes .... ... ... ... ........... ...... ...... ............. ....... ... ......... .... 26
2.3 Hydroboration .................. ............ ........ ...... ...... ........... ..... ................... 27
2.3.1 General Considerations ............................................................ 27
2.3.2 Mechanism of Hydroboration .................................................. 29
2.3.3 Hydroborating Agents .............................................................. 31
2.3.3.1 Borane Sources .......................................................... 31
2.3.3.2 Alkylborane reagents ................................................. 31
2.3.3.3 Oxygen substituted hydroborating agents .................. 32
2.3.3.4 Haloboranes ............................................................... 33
2.3.4 Catalyzed Hydroborations ....................................................... 35
2.4 Haloborations ...... ..... ............... ... ... ...... ... ........ ......... ...... .... ........... ....... 40
2.5 Other Routes to Carbon-Boron Bonds. ........... ........ ..... ....... ............. 41
2.6 References. ..... ....... ............ ......... ......... ...... ......... .... ........... ..... ............. 44
VI Contents
3 General Reactions of Organoboranes ............ ..... .................................... 48
3.1 Introduction ......................................................................................... 48
3.2 Oxidative Replacement of Boron ........................................................ 48
3.2.1 Introduction ............................................................................. 48
3.2.2 Oxygen Electrophiles .............................................................. 49
3.2.2.1 Hydrogen peroxide..................................................... 49
3.2.2.2 Migratory aptitudes .................................................... 51
3.2.2.3 Sodium perborate and other peroxides ...................... 51
3.2.2.4 Trimethylamine N-oxide ............................................ 53
3.2.2.5 Molecular oxygen ...................................................... 53
3.2.2.6 Other reagents ............................................................ 53
3.2.3 Nitrogen Electrophiles ............................................................. 54
3.2.3.1 Chloramine and hydroxylaminesulfonic acid ............ 54
3.2.3.2 Alkyl azides ............................................................... 55
3.2.3.3 Rearrangement of a-aminoboranes ............................ 57
3.2.4 Halogenation ............................................................................ 59
3.2.4.1 Stereoselective replacements ..................................... 59
3.2.4.2 Halogenation at carbon adjacent to boron ................. 59
3.2.5 Sulfur ....................................................................................... 60
3.2.6 Protonolysis ............................................................................. 60
3.2.7 Metalation ................................................................................ 62
3.3 Boron Substituted Carbanions ............................................................ 63
3.3.1 By Deboronation...................................................................... 63
3.3.2 By Destannylation ................................................................... 65
3.3.3 By Deprotonation .................................................................... 65
3.3.4 By Michael Addition ............................................................... 69
3.4 Replacement of Boron by Carbon ....................................................... 71
3.4.1 Introduction ............................................................................. 71
3.4.2 ß-Eliminations as Nuisance Reactions .................................... 71
3.4.3 Migrations to Electron-Deficient a-Carbon ........................... 72
3.4.3.1 Introduction ................................................................ 72
3.4.3.2 Discovery of process and mechanism ........................ 73
3.4.3.3 Favored reaction pathways ........................................ 73
3.4.3.4 Routes to a-haloalkylboron compounds .................... 74
3.4.3.5 The stereocontrollable route to halo boronic esters ... 77
3.4.3.6 Alkylation of (halomethyl)boronic esters .................. 78
3.4.3.7 Simple homologation ofboronic and borinic esters .. 79
3.4.3.8 Rearrangement of a,b-unsaturated borates ................. 80
3.4.3.9 Carbonylation and cyanidation .................................. 82
3.4.3.10 Other chain extensions ............................................... 86
3.4.4 Displacement of Boron by Electrophilic Carbon .................... 88
3.4.4.1 Polar displacements ................................................... 88
3.4.4.2 Small ring formation .................................................. 89
3.4.4.3 Radical displacement mechanisms ............................ 91
3.4.5 Allylborane Chemistry ............................................................ 92
Contents VII
3.4.5.1 Introduction .............................................................. .. 92
3.4.5.2 Triallylborane ............................................................ . 92
3.4.5.3 Intramolecular allylic rearrangements ...................... . 95
3.4.5.4 Allylic bisboranes .................................................... .. 96
3.4.5.5 Three-carbon chain extension ofboronic esters ...... .. 98
3.4.5.6 3-Borolenes ............................................................... . 99
3.4.5.7 Allenyl and propargyl boranes .................................. . 100
3.4.6 Photochemical Rearrangements ............................................ .. 101
3.5 Reactions at Sites Other than the B-C Bond .................................... .. 104
3.5.1 Introduction ............................................................................ . 104
3.5.2 Nucleophilic Reactions of a-Halo Boronic Esters .................. . 104
3.5.2.1 Displacements ........................................................... . 104
3.5.2.2 Eliminations .............................................................. . 106
3.5.3 a-Bromination ......................................................................... 106
3.5.4 Oxidations of Other Functions in the Presence of C-B
Bonds ....................................................................................... 107
3.5.5 Additions to Double Bonds ..................................................... 108
3.5.5.1 Radical additions........................................................ 108
3.5.5.2 Polar and catalytic additions ...................................... 109
3.5.5.3 Cycloadditions ........................................................... 110
3.5.5.4 Cyclopropanation ....................................................... 111
3.6 References ........................................................................................... 112
4 Alkenylboranes and Control of Oletinic Geometry .......... ..................... 120
4.1 Introduction ......................................................................................... 120
4.2 ß-Elimination Routes to Unsaturated Compounds ............................. 120
4.2.1 Simple Alkenes ........................................................................ 120
4.2.1.1 Introduction ................................................................ 120
4.2.1.2 Stereochemistry .......................................................... 121
4.2.1.3 Fragmentation ............................................................ 122
4.2.1.4 Alkenes from enamines .............................................. 122
4.2.2 Routes to Alkenylboranes ........................................................ 123
4.2.2.1 (E)-I-Alkenylboranes from l-alkynes ....................... 123
4.2.2.2 Alkenylboranes from disubstituted alkynes ............... 124
4.2.3 Inversion of (E)-to (Z)-Alkenylboranes .................................. 130
4.2.4 Other Routes to Alkenylboranes .................................. ............ 134
4.2.5 The ZweifelOlefin Synthesis .............................. .................... 136
4.3 The Suzuki Coupling Reaction ........................................................... 139
4.3.1 Scope ofthe Reaction .............................................................. 139
4.3.2 Synthetic Applications ............................................................. 149
4.4 Other Stereoselective Routes to Alkenes ............................................ 155
4.4.1 Alkenylpropargylic and Alkenylallenic Boranes ..................... 155
4.4.2 Insertion into Carbon-Boron Bonds ........................................ 156
4.4.3 a,ß-Unsaturated Ketones from Boron Enolates ........ ,............ 157
4.5 References ........................................................................................... 158
VIII Contents
5 Asymmetrie Synthesis via (a-Haloalkyl)boronie Esters ........................ 162
5.1 Introduction......................................................................................... 162
5.1.1 Overview................................................................................. 162
5.1.2 Nomenclature Notes ................................................................ 163
5.1.2.1 Chirality descriptors ................................................... 163
5.1.2.2 Bond illustration conventions .................................... 164
5.1.2.3 Drawings ofbicyclic structures ................................. 165
5.2 Synthetic Methodology: Pinanediol Esters ........................................ 165
5.2.1 Original Process ....................................................................... 165
5.2.1.1 Preparation ofpinanediol........................................... 165
5.2.1.2 Discovery of pinanediol boronic ester chemistry ...... 166
5.2.1.3 Epimerization of(a-chloroalkyl)boronic esters ......... 168
5.2.2 Zinc Chloride Promotion of a-Halo Boronic Ester
Formation................................................................................. 169
5.2.3 Functional Group Compatibility.............................................. 171
5.2.3.1 Alkoxy substituents .................................................... 171
5.2.3.2 An azido substituent ................................................... 173
5.2.3.3 Thioether substituents ................................................ 175
5.2.3.4 Halogen substituents .................................................. 175
5.2.3.5 Carboxylic ester substituents ..................................... 175
5.2.3.6 Unsaturated boronic esters ......................................... 176
5.2.4 Quatemary Chiral Centers ....................................................... 177
5.2.5 Pinanediol Recovery ................................................................ 179
5.2.6 Nonequivalent Faces of Boron in Pinanediol Esters ............... 180
5.3 Synthetic Methodology: Chiral Directors Having C Symmetry ....... 181
2
5.3.1 Butanediol Esters ..................................................................... 181
5.3.1.1 Synthetic routes made possible by C symmetry ....... 181
2
5.3.1.2 Nomenclature of cyclic boronic esters ....................... 183
5.3.2 Diisopropylethanediol (DIPED) Esters ................................... 183
5.3.2.1 Introduction ................................................................ 183
5.3.2.2 Synthesis of DIPED ................................................... 183
5.3.3 Dicyclohexylethanediol (DICHED) Esters ............................. 184
5.3.3.1 Introduction ................................................................ 184
5.3.3.2 Synthesis of DICHED ................................................ 184
5.3.4 Ultrahigh Stereoselectivity with C2 Symmetry ....................... 185
5.3.4.1 Introduction ................................................................ 185
5.3.4.2 Background ................................................................ 185
5.3.4.3 Discovery of enhanced selectivity ............................. 185
5.3.4.4 Kinetic resolution ....................................................... 186
5.3.4.5 Mechanistic interpretation ......................................... 187
5.3.5 Convergent Connection of Two Asymmetrie Centers ............. 189
5.3.6 Reaction ofEnolates ................................................................ 192
5.3.7 Allylic Boronic Esters ............................................................. 193
5.3.7.1 (a-Haloallyl)boronic esters ........................................ 193
Contents IX
5.3.7.2 Asymmetrie synthesis of an allylie boronie ester ...... 194
5.3.7.3 Chain extension of allylboronie esters ....................... 194
5.4 Synthetic Applieations ........................................................................ 195
5.4.1 A Useful Mnemonie for Chiral Direetion................................ 195
5.4.2 Amido Boronie Esters ............................................................. 196
5.4.3 Inseet Pheromones ................................................................... 203
5.4.3.1 Introduetion ................................................................ 203
5.4.3.2 exo-Brevicomin .......................................................... 203
5.4.3.3 Eldanolide .................................................................. 204
5.4.3.4 (3S,4S)- and (3R,4S)-4-Methyl-3-heptanol ................ 205
5.4.3.5 Stegobiol and stegobinone ......................................... 207
5.4.4 Polyols ..................................................................................... 209
5.4.4.1 L-Ribose ..................................................................... 209
5.4.4.2 Asymmetrieally deuterated glyeerol.......................... 212
5.4.5 Amino Acids ............................................................................ 215
5.5 Referenees ........................................................................................... 218
6 Asymmetrie Hydroboration Chemistry ..... ............ ... ..... ......................... 221
6.1 Introduction . ....... ... ...... ......... ......... ........ ...... .......... ......... .................. ... 221
6.2 Asymmetrie Hydroboration . ... ...... ........ .................... ..... ..... ................ 222
6.2.1 Reagents. ... ...... ...... ... ... .......... ...... .... ........ ...... ..... ....... ...... ... ...... 222
6.2.1.1 Purifieation of pinylboranes . ...... ............. ... ................ 222
6.2.1.2 Recovery of a-pinene ................................................ 223
6.2.1.3 Alternative ehiral direetors ........................................ 224
6.2.2 Hydroboration with Diisopinoeampheylborane ...................... 226
6.2.3 Hydroboration with Monoisopinoeampheylborane ................. 230
6.3 Transformations of Asymmetrie Organoboranes ............ ...... .............. 233
6.3.1 Overview ................................................................................. 233
6.3.1.1 General summary of transformations ......................... 233
6.3.1.2 Intereonversions of boron oxidation states ................ 235
6.3.2 Carbon-Carbon Bond Formation .......................................... 236
6.3.2.1 Introduction ................................................................ 236
6.3.2.2 Methylene insertion routes ......................................... 236
6.3.2.3 Borinie ester intermediates ........................................ 238
6.3.2.4 Enolate insertions ....................................................... 240
6.3.2.5 Thexylborane and pinylborane intermediates ............ 241
6.3.3 Carbon-Nitrogen Bond Formation ........................................ 245
6.4 Substrate Direeted Hydroboration ...................................................... 247
6.4.1 Noneatalytie methods .............................................................. 247
6.4.1.1 Introduction................................................................ 247
6.4.1.2 Isopropenyl group hydroboration .............................. 247
6.4.1.3 Cyc1ie borane intermediates ............. ..... ..... ............ .... 248
6.5 Catalytie Asymmetrie Hydroboration ................................................. 251
6.5.1 Catalyst Effeets in Substrate Direeted Hydroboration ............ 251
X Contents
6.5.2 Hydroboration with Asymmetrie Catalysts ............................. 254
6.6 Referenees .......... .............................................................................. ... 257
7 AlIylboron and Boron Enolate Chemistry ............................... ..... .......... 260
7.1 Introduetion ......................................................................................... 260
7.2 Allylie Boronie Esters ......................................................................... 261
7.2.1 General Advantages ...................... ........................... ... .......... ... 261
7.2.2 Sources of Allylie Boronie Esters ...... ................................ ...... 261
7.2.2.1 Allylie metal eompounds ........................................... 261
7.2.2.2 Retroraeemization of a Grignard reagent .............. ..... 262
7.2.2.3 Via (alkenyl)(halomethyl)borate rearrangement ........ 263
7.2.2.4 Catalyzed hydroboration . ........................... .... ... ......... 263
7.2.3 Diastereoseleetion with Racemates ......................................... 264
7.2.3.1 Meehanism ................................................................. 264
7.2.3.2 Range ofuseful substituents ...................................... 266
7.2.3.3 Imines ......................................................................... 267
7.2.3.4 Ketones ...................................................................... 267
7.2.3.5 Cyclizations ................................................................ 269
7.2.4 Asymmetrie Reaetions ofBoronie Esters................................ 271
7.2.4.1 Boronie esters of ehiral diols with aehiral
aldehydes ................................................................................. 271
7.2.4.2 A ehiral boron amide ................................................. 275
7.2.4.3 Chiral Aldehydes ........................................................ 276
7.2.4.4 Chiral allylie groups ................................................... 282
7.2.5 Asymmetrie Syntheses with Boronie Esters ............................ 288
7.2.5.1 Inseet pheromones ..................................................... 288
7.2.5.2 Maerolide and ionophore antibiotie syntheses ........... 290
7.2.6 Allenyl and Propargyl Boronie Esters and 1.3.2-Diaza
borolidines ............................................................................... 299
7.2.7 Borinie Acids .......................... ................................................. 300
7.3 Allyldialkylboranes............................................................................. 301
7.3.1 From a-pinene and other terpenes ........................................... 301
7.3.1.1 Unsubstituted allyl groups ......................................... 301
7.3.1.2 Methyl-substituted allyl groups ................................. 301
7.3.1.3 Other substituted allyl groups .................................... 307
7.3.2 Borolanes as Chiral Direetors .................................................. 308
7.4 Boron Enolates ............. ................... .................................................... 311
7.4.1 Introduction ............................................................................. 311
7.4.2 Chiral Enolate Carbon Skeletons ........................ ................. .... 311
7.4.2.1 Silylated hydroxy ketone enolates ............................. 311
7.4.2.2 Chiral amide enolates ................................................. 312
7.4.3 Chiral Boryl Groups ................................................................ 313
7.4.3.1 2,5-Dimethylborolanes ............................................... 313
7.4.3.2 Chirall,3,2-diazaborolidines ..................................... 316
