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Applications of Organic Photoredox Catalysis in the Development of Alkene Functionalization Methods Toward the Synthesis of Α– Benzyloxyamino- and Halo-Lactones

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Applications of Organic Photoredox Catalysis in the Development of Alkene Functionalization Methods Toward the Synthesis of Α– Benzyloxyamino- and Halo-Lactones APPLICATIONS OF ORGANIC PHOTOREDOX CATALYSIS IN THE DEVELOPMENT OF ALKENE FUNCTIONALIZATION METHODS TOWARD THE SYNTHESIS OF α– BENZYLOXYAMINO- AND HALO-LACTONES Cortney L. Cavanaugh A dissertation submitted to the faculty at the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Department of Chemistry. Chapel Hill 2018 Approved by: David Nicewicz Simon Meek Jeffrey Aubé Michel Gagné Frank Leibfarth © 2018 Cortney L. Cavanaugh ALL RIGHTS RESERVED ii ABSTRACT Cortney L. Cavanaugh: APPLICATIONS OF ORGANIC PHOTOREDOX CATALYSIS IN THE DEVELOPMENT OF ALKENE FUNCTIONALIZATION METHODS TOWARD THE SYNTHESIS OF α–BENZYLOXYAMINO- AND HALO-LACTONES (Under the direction of David A. Nicewicz) I. Introduction To Organic Photoredox Catalysis An overview of the photophysical and electrochemical components of organic photoredox catalysis and its applications in alkene functionalization reactions is addressed. II. Synthesis of α-Benzyloxyamino-γ-Butyrolactones Via a Polar Radical Crossover Cycloaddition Reaction The development of a direct catalytic synthesis of substituted α-benzyloxyamino-γ- butyrolactones, beginning from simple oxime acids and alkenes, is discussed. The substituted O- benzyloxime acid starting materials undergo cyclization with oxidizable alkenes, via Polar Radical Crossover Cycloaddition (PRCC) reactions. The catalytic reaction is carried out using an acridinium photooxidant and substoichiometric amounts of a redox-active cocatalyst. The utility of this methodology is demonstrated through the cyclization of 3 oxime acids and 19 oxidizable olefins to generate 21 highly substituted α-amino lactone products. III. Reversing The Regioselectivity Of Halofunctionalization Reactions Through Cooperative Photoredox And Copper Catalysis A novel method for reversing the regioselectivity of classic alkene halofunctionalization reactions is presented. This transformation relies on the implementation of a dual-catalytic system, incorporating the use of an acridinium photoredox catalyst in conjunction with a coppercocatalyst. The utility of the method is demonstrated through the application of chloro- iii and bromo-functionalization conditions in both an intra- and intermolecular fashion. Over 15 synthetically and biologically relevant halo-lactones are accessed in a highly regioselective fashion. iv To my mom and dad, thank you for making all of this possible. v ACKNOWLEDGEMENTS There is no way I can thank my parents enough for their encouragement and support throughout life, but especially through my graduate school career. I can genuinely say that none of this would have been possible without them. I would also like to thank my twin brother Michael for never letting me take myself too seriously and keeping me laughing through our shared trudge through graduate school. Leaving my family to pursue my degree was a painful decision but they have been there all along the way to keep me motivated and pushing forward. I would like to thank you with all of my heart for that. Thank you to my friends, at UNC and beyond, for making the tough times easier. Despite all of its challenges, graduate school wasn’t without fun times and laughter. I am especially appreciative to Jake Green. I couldn’t have been luckier to meet my best friend who was there through every struggle and accomplishment I encountered. Additionally, graduate school would have been unimaginable without my roommate Lilo who always kept me smiling. I am grateful to my PI, David Nicewicz, for supporting me through this entire process and giving me the opportunity to learn so much throughout my time at UNC. I owe an additional thank you to the Nicewicz lab, past and present, for their help and camaraderie. Thank you to Jeremy Griffin for his support on the halofunctionalization project and to Cole Cruz for helping me survive this process. Finally, I would like to thank those who have served as members of my defense committee for their time and commitment. vi TABLE OF CONTENTS LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES .........................................................................................................................x LIST OF SCHEMES ..................................................................................................................... xi LIST OF ABBREVIATIONS AND SYMBOLS ..........................................................................xv CHAPTER ONE: INTRODUCTION TO ORGANIC PHOTOREDOX CATALYSIS 1.1 Introduction ....................................................................................................................1 1.2 The Photophysical and Electrochemical Components of Photoredox Catalysis ...........1 1.3 Organic Photoredox Catalysis and its Applications in Anti-Markovnikov Alkene Hydrofunctionalization ............................................................................................9 1.3.1 Selecting an Effective Organic Photoredox Catalyst ........................11 1.3.2 Mechanistic Insight ...........................................................................14 1.4 Conclusion ...................................................................................................................17 1.4 References ....................................................................................................................18 CHAPTER TWO: SYNTHESIS OF α-BENZYLOXYAMINO-γ-BUTYROLACTONES VIA A POLAR RADICAL CROSSOVER CYCLOADDITION REACTION 2.1 Introduction ..................................................................................................................20 2.2 Synthesis of α-Amino-γ-Butyrolactones ...................................................................21 2.3 Synthesis of α-Benzyloxyamino-γ-Butyrolactones via Photoredox Catalysis ............26 2.3.1 Background and Precedent ...............................................................26 2.3.2 Results and Discussion .....................................................................39 2.4 Conclusion .....................................................................................................................5 vii 2.5 Experimental ................................................................................................................54 2.6 References ..................................................................................................................110 CHAPTER THREE: REVERSING THE REGIOSELECTIVITY OF HALOFUNCTION- ALIZATION REACTIONS THROUGH COOPERATIVE PHOTOREDOX AND COPPER CATALYSIS 3.1 Introduction ........................................................................................................................................ 113 3.2 Halofunctionalization of Alkenes ............................................................................................... 116 3.3 Synthesis of Halolactones .............................................................................................................. 118 3.4 Halofunctionalization Achieved Through Photoredox Catalysis ..................................... 127 3.4.1 Background and Precedent ........................................................................... 127 3.4.2 Results and Discussion .................................................................................. 134 3.5 Conclusion .......................................................................................................................................... 155 3.6 Experimental ...................................................................................................................................... 157 3.7 References ........................................................................................................................................... 215 viii LIST OF TABLES Table 2-1. Optimization Of PRCC Conditions For The Synthesis Of α-Benzyloxyamino-γ-Butyrolactones ................................................................................40 Table 2-2. Exploration Of Reduction Conditions To Access The Free Amine Product ................49 Table 2-3. Exploration Of Acylation Conditions To Access The N-Acyl Amine .........................50 Table 3-1. Scope And Regioselectivity Of CSCS Catalyzed Chlorolactonization ......................125 Table 3-2. Catalyst Recyclability .................................................................................................125 Table 3-3. Optimization of Photoredox Mediated Anti-Markovnikov Hydroetherification ..........................................................................................................126 Table 3-4. Optimization Of Chlorolactonization Conditions ......................................................137 Table 3-5. Optimization Of Bromolactonization Conditions ......................................................142 ix LIST OF FIGURES Figure 1-1. Jablonski Diagram And A Simplistic View Of Excitation/ISC ....................................2 Figure 1-2. Single Electron Transfer Model ....................................................................................3 Figure 1-3. Series Of Potentials For Various Organic Functional Groups And Catalysts ..............7 Figure 1-4. Photophysical Properties Of 9-Mesityl-10-Methylacridinium Photoredox Catalyst ...........................................................................................................13 Figure 2-1. Natural
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