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The Investigation of Organoboron Compounds and Organoboron/Nitrone Reactions" (1991)

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The Investigation of Organoboron Compounds and Organoboron/Nitrone Reactions W&M ScholarWorks Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects 1991 The Investigation of Organoboron Compounds and Organoboron/ Nitrone Reactions David Kent Hood College of William & Mary - Arts & Sciences Follow this and additional works at: https://scholarworks.wm.edu/etd Part of the Organic Chemistry Commons Recommended Citation Hood, David Kent, "The Investigation of Organoboron Compounds and Organoboron/Nitrone Reactions" (1991). Dissertations, Theses, and Masters Projects. Paper 1539625664. https://dx.doi.org/doi:10.21220/s2-bg7f-pj23 This Thesis is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. The Investigation of Organoboron Compounds and Organoboron/Nitrone Reactions A Thesis Presented to The Faculty of the Department of Chemistry The College of William and Mary in Virginia In Partial Fulfillment Of the Requirements for the Degree of Masters of Arts by David K. Hood 1991 Approval Sheet This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Arts David K. Hood Approved, December 1991 Christopher J/l Abelt W. Hollis William H. Starnes Table of Contents Acknowledgements ...................... ............................................... iv List of Figures and Tables ............................................................. v Abstract........................................................ ............................ viii Chapter 1: Synthesis and Preparation of Organoboron Compounds 2 Overview ........................................................................ 2 Hydroboration .................................................................. 3 Oxidation ........................................................................ 8 Protonolysis .................................................................... 9 Reduction of Functional Groups via Hydroborates ..................... 10 Results and Discussion ....................................................... 12 References ...................................................................... 24 Chapter 2: Reactions of Organoboron Compounds with Nitrones .............. 26 Overview ........................................................................ 26 Rearrangements ............................................................ 32 Nitrones ......................................................................... 33 Results and Discussion ....................................................... 37 References .................... ................................................. 43 Experimental....................... ...................................................... 44 Boronic Acids .................................................................. 44 Boronate Esters ................................................................. 45 Anhydrides ...................................................................... 47 Silyl Ethers...................................................................... 47 THP Ethers..................................................................... 48 Nitrones and Hydroxylamines ............................................... 49 i i i Acknowledgements The author wishes to express his appreciation to Professor W. Gary Hollis, under whose guidance this investigation was conducted, for his patience, expert instruction, and constructive criticism throughout the investigation. The author is also indebted to Professors Christopher J. Abelt and William H. Starnes for their careful reading and criticism of this manuscript. A word of thanks is due to the Chemistry Department at the College of William and Mary for their encouragement and assistance over the last five years. The time spent in this program has been both rewarding and enjoyable. Finally, a special thank you to my family, old and new, and to my closest friends who have provided me with continuous encouragement. iv List of Figures and Tables Chapter 1 Figure 1: Preparation of Triethylborane ........................................... 2 Figure 2: General Preparation of Alcohols ........................................ 2 Figure 3: Graphic Description of the Hydroboration Reaction ............... 3 Figure 4: General Types of Hydroborating Reagents ............................. 4 Figure 5: General Reaction for the Hydroboration of Alkenes ................. 5 Table 1: Site Selectivity of Some Hydroborations ............................... 6 Figure 6 : General Reaction for the Hydroboration of Alkynes ................ 6 Table 2: Directive Effects of Dialkylboranes ...................................... 6 Table 3: Directive Effects in the Hydroboration of 1-Hexene ................ 7 Figure 7: General Preparation of Alkynylborates ................................ 7 Figure 8 : Mechanism of the Oxidation of a Trialkylborane via a Hydroperoxide Anion ............................................. 9 Figure 9: Transition State for the Protonolysis of Organoboranes 10 Table 4: Chemoselectivities of Boron-Containing Reducing Agents 11 Figure 10: Reduction of Ethyl 8 -chloro- 6 -oxooctanoate with NaBH 4 12 Figure 11: Preparation of (E)-l-Hexenylboronic Acid .......................... 13 Figure 12: Preparation of (E)-l-Hexenyl Ethylene Glycol Ester .............. 14 Figure 13: General Preparation of Dialkyl Vinyl Boronate Ester .............. 15 Figure 14: Preparative Yields of a, 8 -Unsaturated Organoboron Compounds. 16 Figure 15: Resonance Forms of Boronic Acid and Carboxylic Acid 17 Table 5: Vinyl Proton Chemical Shifts of Various (E)-1-Alkenyl Boronic Esters, Acids, and Anhydrides .......................... 18 Figure 16: Attempted Preparation for Boracycles .............................. 19 Figure 17: General Preparation for Tetrahydropyranyl Ethers .................. 20 Figure 18: General Preparation for Silyl Ethers ................................... 21 Figure 19: Preparative Yields of Silyl Ethers ...................................... 22 Figure 20: Preparative Yields of Tetrahydropyranyl Ethers ..................... 23 v Chapter 2 Figure 1: Preparation of endo- and exo- 5-Norbomane-2-boronate 26 Figure 2: Preparation of Dibutylnorbomadiene-2-boronate ......... 27 Figure 3: General Form of a 1,3-Dipolar Cycloaddition ....................... 27 Figure 4: Resonance Forms of Vinyl Boronic Acid ............................. 28 Figure 5: Examples of the Stereospecificity in 1,3 -Dipolar Cycloadditions..28 Figure 6 : Examples of the Stereospecificity in 1,3-Dipolar Cycloadditions..29 Figure 7: Examples of Favorable Secondary Frontier Orbital Interactions in a 1,3-Dipolar Cycloaddition .................................... 29 Figure 8 : Example of 1,3-Dipolar Cycloaddition Stereoselectivity 30 Figure 9: Electron Demand in a HOMO/LUMO Analysis of Diazomethane and a Dipolarophile .................................................. 31 Figure 10: Orbital Coefficient Analysis of Diazomethane and a Dipolarophile 31 Figure 11: 1,3-Dipolar Cycloaddition Transition State .......................... 32 Figure 12: Homologation via Rearrangement Reaction .......................... 33 Figure 13: 1,2-Rearrangement via Trimethylamine Oxide and a Trialkylborate Compound ........................................... 33 Figure 14: General Reduction of an a,B-Unsaturated Nitro Compound 34 Figure 15: General Preparation for Diphenylnitrone .............................. 35 Figure 16: General Preparation for a Nitrone via Oxidation of an Hydroxylamine ....................................................... 35 Table 1: Mass Spectral Data for a,N-Diphenylnitrone ........................ 36 Table 2: *H NMR Data for a,N-Diphenylnitrone....... ....................... 37 Figure 17: Preparative Yields for Some Diphenylnitrones ....................... 39 Figure 18: Reaction Mechanism for the Rearrangement Reaction a,N-Diphenylnitrone and Triethylborane. Preparative Yields for N,N-Disubstituted Hydroxylamines ................. 40 Table 3: *H NMR Data for Prepared N,N-Disubstituted Hydroxylamines. 41 Table 4: ^ C NMR Data for Prepared N,N-Disubstituted Hydroxylamines ..................................................... 41 v i Mass Spectral Data for Prepared N,N-Disubstituted Hydroxylamines ................................................. Abstract The primary objective of this research was to prepare various a,B-unsaturated organoboron compounds and study their reactive properties. Many (E)-l-alkenyl boranes, boronic acids, anhydrides, and boronates were prepared and characterized utilizing NMR and GCMS techniques. Numerous attempts were made to prepare 1-alkynyl boronates but none of these attempts were successful. The reactive properties of these a,B-unsaturated organoboron compounds were studied via their reactions with nitrones. There is no prior documentation for this type of reaction. As a result of this research, three new compounds were produced via a rearrangement alkylation reaction between these nitrones and commercially available triethyl borane. The synthesis of these new compounds enabled the development of a new carbon-carbon bond and a new chiral center. These new compounds were characterized using IR, GCMS, and NMR techniques. v i i i Chapter 1 Synthesis and Preparation of Organoboron Compounds Historical Overview The first synthesis of an organoborane was reported by
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