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UC Santa Cruz Electronic Theses and Dissertations UC Santa Cruz UC Santa Cruz Electronic Theses and Dissertations Title OBSERVATIONS IN REACTIVITY BETWEEN BH CONTAINING COMPOUNDS AND ORGANOMETALLIC REAGENTS: SYNTHESIS OF BORONIC ACIDS, BORONIC ESTERS, AND MAGNESIUM HYDRIDES Permalink https://escholarship.org/uc/item/113107h0 Author Clary, Jacob William Publication Date 2012 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA SANTA CRUZ OBSERVATIONS IN REACTIVITY BETWEEN BH CONTAINING COMPOUNDS AND ORGANOMETALLIC REAGENTS: SYNTHESIS OF BORONIC ACIDS, BORONIC ESTERS, AND MAGNESIUM HYDRIDES A dissertation submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in CHEMISTRY AND BIOCHEMISTRY by Jacob William Clary March 2012 The Dissertation of Jacob W. Clary is approved: Professor Bakthan Singaram, Advisor Professor Rebecca Braslau, Chair Professor Claude Bernasconi Tyrus Miller Vice Provost and Dean of Graduate Studies Copyright © by Jacob W. Clary 2012 ii TABLE OF CONTENTS LIST OF FIGURES viii LIST OF SCHEMES x LIST OF TABLES xii ABSTRACT xviii DEDICATION AND ACKNOWLEDGEMENTS xv CHAPTER 1. Review of Boronic Acid Synthesis and Applications 1 1.1 Introduction 2 1.1.1 Nomenclature of Boronic Acids 3 1.1.2 Properties of Boronic Acids 5 1.1.3 Analysis of Boronic Acids 7 1.2 Boronic Acids in Organic Chemistry 9 1.2.1 Suzuki-Miyaura C-C Cross-Coupling 9 1.2.1.1 Applications of the Suzuki-Miyaura Cross-Coupling Reaction 11 1.2.1.2 Mechanism of the Suzuki-Miyaura Cross-Coupling 15 1.2.2 Stereoselective Suzuki Cross-Coupling 16 1.2.3 C-N and C-O Cross-Coupling Reactions with Boronic Acids 23 1.2.4 Biological and Medicinal Applications 26 1.3 Synthesis of Boronic Acids 31 1.3.1 Transmetallation of Grignard and Organolithium Reagent 32 iii 1.3.2 Cross-coupling Reaction of Bis(pinacolato)diboron and Pinacolborane 34 1.3.3 C-H Activation 40 1.4. Conclusion 41 1.5. Thesis Outline 42 1.6. References 44 CHAPTER 2. Reaction of Grignard Reagents with Diisopropylaminoborane. Synthesis of Alkyl, Aryl, Heteroaryl and Allyl Boronic Acids From Organo(diisopropylamino)borane By A Simple Hydrolysis 55 2.1 Introduction 56 2.2 Properties and Structural considerations of aminoboranes 63 2.3 Current Methods of Aminoborane Synthesis 65 2.3.1 Thermal Dehydrogenation 65 2.3.2 Reduction of (amino)dihaloboranes 67 2.3.3 Metal Catalyzed Dehydrogenation 67 2.4 Results and Discussion 69 2.4.1 New Methods of Aminoborane Synthesis 69 2.4.2 Reactivity of Aminoboranes 78 2.4.2.1Vaultier Borylation 78 2.4.2.2 Hydroboration of Alkenes and Alkynes 79 2.4.2.3 Synthesis of Boronic Acids via Grignard Reagents 82 2.4.2.4 Synthesis of Boronic Acids under Barbier Conditions 88 2.5 Conclusions 91 2.6 Experimental 92 iv 2.7 References 105 Chapter 3. Synthesis of Magnesium Hydride and Reduction of Weinreb Amides 110 3.1 Introduction 111 3.2 Magnesium Hydride 112 3.3 Hydridomagnesium Halides 116 3.4 Properties and Synthesis of N-Methoxy-N-methylamides (Weinreb Amides) 121 3.4.1 Properties of Weinreb Amides 121 3.4.2 Synthesis of Weinreb Amides 124 3.5 DIBAL and LAH Reduction of Weinreb Amides 126 3.6 Results and Discussion 129 3.6.1 Vinylmagnesium Bromide Addition to Phenyl Weinreb Amide 129 3.6.2 Synthesis of Hydridomagnesium Halide from Grignard and Pinacolborane 132 3.6.3 Analysis of Hydridomagnesium Halide 134 3.6.4 Computation Analysis of HMgBr Disproportionation 144 3.6.5 Partial Reduction of a Weinreb Amide Using Magnesium Hydride 146 3.6.6 Partial Reduction of Weinreb Amide using ChloroMagnesium Aminoborohydride 150 3.7 Conclusions 151 3.8 Experimental 153 3.9 References 160 v CHAPTER 4. Reaction of Pinacolborane With Halides Under Grignard and Barbier Conditions. One Pot Synthesis of Pinacol Alkyl, Aryl, Heteroaryl, Vinyl and Allylboronic Esters 162 4.1 Introduction 163 4.2 Stability of Pinacol Arylboronates 164 (2-organo-4,4,5,5-tetramethyl-1,3,2-dioxaborolane) 4.3 Properties of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (pinacolborane) 167 4.3.1. Synthesis of Pinacolborane 167 167 4.4 Results and Discussion 169 169 4.4.1 Reactivity of Organometallic Reagents with Boron Species Containing a B-H Bond 169 169 4.4.2 Stability of Pinacolborane 174 174 4.4.3 Reaction Characterization 177 177 4.4.3.1 Examination of Reaction Products 177 177 4.4.4 Syntheses of Alkyl and Aryl Pinacol Boronates Using Preformed Grignard Reagents 181 181 4.4.5 Syntheses of aryl and alkyl pinacol boronates using Mg° under Barbier-type Conditions 184 184 4.4.6 Synthesis of Allylboronates Under Barbier Conditions 186 4.4.7 One Pot Synthesis of Haloarylboronic Acids 188 4.5 Conclusions 192 4.6 Experimental 193 4.7 References 210 vi Appendix A: CHAPTER 2. 11B, 1H, 13C NMR Spectra 215 Appendix B CHAPTER 3. 11B, 1H, 13C NMR Spectra, X-Ray Crystal Structures, DFT Calculations 270 Appendix C CHAPTER 4. 11B, 1H, 13C NMR Spectra 330 Bibliography 420 vii LIST OF FIGURES Figure 1.1. Borane dimer, diborane (B2H6) 3 Figure 1.2. Organic and oxygenated boron compounds 4 Figure 1.3. Boronic acid esterification 5 Figure 1.4. Common optically active diols 5 Figure 1.5. A. Illustration of tartaric acid crystals B. (S,S) and (R,R) tartaric acid 18 Figure 1.6. Michellamine B 21 Figure 1.7. Diastereoselective (path a and b) vs. enantioselective (path c) Suzuki cross-coupling 21 Figure 1.8. Bortezomib (Velcade®) 30 Figure 1.9. Boron containing pharmacophores 31 Figure 1.10. PdCl2(dppf) (dppf = 1,1’-bis(diphenylphosphino)ferrocene) 35 Figure 2.1. Examples of -methyl alcohols 57 Figure 2.2. Aminoboranes: monomers and monomer/dimer mixtures 72 Figure 2.3. Catalytic cycle in the reaction of Et3B with LAB and methyl iodide 73 Figure 2.4. Dimers of (a) pyrazolylborane and (b) pyrrolylborane 77 Figure 2.5. A. Proposed reaction pathways. B. 11B NMR Spectrum of reaction mixture 82 Figure 3.1. Proposed liner polymer of MgH2. 114 Figure 3.2. Proposed molecular structure of dimeric HMgX 118 viii Figure 3.3. Various carboxylic acid activating agents for Weinreb amide synthesis 126 Figure 3.4. X-ray structure of Mg-TMEDA complex 136 11 Figure 3.5. Reaction of BH3:THF with magnesium hydride byproduct. A. B- 11 NMR of BH3:THF B. B-NMR at 2 h of BH3:THF + MgH2 stirred at 25 °C 139 Figure 3.6 Gas burette for measuring volume of gas evolved 140 Figure 3.7 A. The μHBr-bridged HMgBr dimer is the key intermediate in the Schlenk equilibrium. B. Schematic reaction coordinate state diagram for the Schlenk equilibrium, energies are in kcal/mol relative to 2HMgBr 147 Figure 4.1. Partial molecular orbital view of (2-aryl-4,4,5,5-tetramethyl-1,3,2- dioxaborolane) 164 Figure 4.2. Crystal sturcture of p-tolylpinacolboronate 174 Figure 4.3. Analysis of pinacolborane stability in various solvents, by 11B NMR spectroscopy 175 Figure 4.4. 11B NMR spectrum of pinacolborane stored neat for 7.5 months 177 ix LIST OF SCHEMES Scheme 1.1. Suzuki-Miyaura cross-coupling 9 Scheme 1.2. Industrial synthesis of Boscalid® 12 Scheme 1.3. Solid support-bound palladium catalyzed cross-coupling reaction of organoboranes and aryl and alkenyl halides and triflates 14 Scheme 1.4. Catalytic cycle for Suzuki-Miyaura cross-coupling 17 Scheme 1.5. Synthesis of (R)-1-acetamido-2-phenylethaneboronic acid 27 Scheme 1.6. Proposed rational for observed diastereoselectivity 29 Scheme 2.1. Borotropic rearrangement of crotylboronates 60 Scheme 2.2. Hydroboration of ,-disubstituted enamines 69 Scheme 2.3. Preparation of morpholinoborane from LAB and methyl iodide 71 Scheme 2.4. General Synthesis of aminoborane from LAB and TMS-Cl 74 Scheme 2.5. Synthesis of pyrrolylborane 76 Scheme 2.6. Palladium catalyzed synthesis of boronic acids from aryl bromides and H2BN(iPr)2 78 Scheme 2.7. Hydroboration of styrene with pyrrolylborane 79 Scheme 2.8. Hydroboration of phenylacetylene with pyrrolylborane 80 Scheme 2.9. Testing the ability of hydridomagnesium chloride to transfer hydride to BH2-N(iPr)2 81 Scheme 2.10. Conversion of arylaminoborane to boronic acid by the addition of water 83 Scheme 3.1. Methods of MgH2 synthesis 112 x Scheme 3.2. Mg-Anthracene catalyzed MgH2 generation 114 Scheme 3.3. Reaction of Grignard with diborane 117 Scheme 3.4. Synthesis of alkoxy and dialkylaminomagnesium hydrides 119 Scheme 3.5. Synthesis of Weinreb amide using BOP activation 125 Scheme 3.6. Synthesis of-bicyclohomofarnesal and its endo isomer 129 Scheme 3.7. Formation of arylboronic ester and HMgBr 133 Scheme 3.8. Stoichiometry of MgH2 formation 135 Scheme 4.1. Synthesis of pinacolborane 167 Scheme 4.2. Equilibrium between arylmagnesiumborohydride and borane in THF 171 Scheme 4.3. Reaction between phenyllithium and pinacolborane 173 Scheme 4.4. Synthesis of p-tolyl pinacolboronate 178 Scheme 4.5. Proposed mechanism for trialkylborohydride formation 179 Scheme 4.6. One pot synthesis of 5,5-dimethyl-2-m-tolyl-1,3,2-dioxaborinane 185 xi LIST OF TABLES Table 1.1. Compounds synthesized by Suzuki-Miyaura cross-coupling 15 11 Table 2.1. B-NMR Spectroscopy of aminoboranes (H2BNR2) prepared in hexanes from LAB and methyl iodide 62 Table 2.2. Aminoboranes synthesized from LAB and TMS-Cl 71 Table 2.3. Aminoboranes synthesized from heterocyclic amines and BH3:THF 76 Table 2.4. Synthesis of boronic acids using preformed Grignard reagents 86 Table 2.5. Synthesis of boronic acids under modiefied Barbier conditions 89 Table 3.1.
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