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Controlling Transition Metal-Catalyzed Alkyne Annulations Utilizing Polarized Ynol Ethers

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University of Denver Digital Commons @ DU Electronic Theses and Dissertations Graduate Studies 2020 Controlling Transition Metal-Catalyzed Alkyne Annulations Utilizing Polarized Ynol Ethers Brandon L. Coles-Taylor Follow this and additional works at: https://digitalcommons.du.edu/etd Part of the Organic Chemistry Commons Controlling Transition Metal-Catalyzed Alkyne Annulations Utilizing Polarized Ynol Ethers ______________ A Dissertation Presented to the Faculty of the College of Natural Sciences and Mathematics University of Denver ____________ In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy ____________ by Brandon L. Coles-Taylor June 2020 Advisor: Brian Michel, PhD ©Copyright by Brandon L. Coles-Taylor 2020 All Rights Reserved Author: Brandon L. Coles-Taylor Title: Controlling Transition Metal-Catalyzed Alkyne Annulations Utilizing Polarized Ynol Ethers Advisor: Brian Michel, PhD Degree Date: June 2020 Abstract Transition metal-catalyzed alkyne annulations have developed into incredibly powerful synthetic tools over there the past quarter century. These reactions provide rapid access to important organic scaffolds such as indole, quinoline, isoquinoline, indene, and isocoumarin scaffolds. Transition metal mediated alkyne annulations have proven invaluable in synthetic fields, such as natural product total synthesis, by offering efficient pathways to otherwise synthetically difficult to access substrates. Foundational works performed by chemist such as Larock, Ackermann, Satoh, and Miura have been established through relying upon the usage of symmetrical alkynes. When unsymmetrical alkynes are used in annulation processes mixtures of regioisomers are often isolated. While methodologies have been developed which regioselectively deliver annulation products, the regioselective nature of these reactions is often empirically determined and obtained with little synthetic design to impact the alkyne migratory insertion step of the catalytic cycle. In recent years few examples of polarized, unsymmetrical alkynes have been sparingly used in transition metal alkyne annulations. Still, these limited examples provide the roadmap for how to regioselectively control alkyne annulations. Researchers have displayed that one class of polarized alkynes, ynol ethers, exhibit the ability to react regioselectively in transition metal-catalyzed migratory insertion processes. There has been ii little research focused on expanding this regioselective nature of ynol ethers into transition metal-catalyzed alkyne annulations. This dissertation provides the work we have accomplished in efforts to bridge this gap. We have established the use of ynol ethers as compatible annulations partners in transition metal-catalyzed alkyne annulations. They have been utilized in the regioselective synthesis of diverse 4-oxy-substituted isoquinolinones. These substrates can be further functionalized into prolyl-4-hydroxylase domain inhibitor analogues. Ynol ethers were also employed to regioselectively facilitate the palladium catalyzed synthesis of complex indenol ethers. Through inhibiting the terminal step in this indene synthesis, -hydride elimination and intercepting the in-situ generated palladium intermediate, the isolation of an enantiomeric mixture of isomers was observed. To date we have partially optimized a regioselective, enantioselective, intermolecular Heck–Suzuki–Miyaura cascade reaction. Further investigation is necessary to fully understand regioselective transition metal- catalyzed ynol ether annulations, but the groundwork has been laid for this work to continue. iii Acknowledgements I would like to acknowledge Benjamin L. Taylor and Natalie M. Brierre, my father and mother, for all their love and support throughout the years. Even when times look bleak you are always in my corner. I am forever grateful. To Ryan S. Taylor, my brother, thanks for your constant support and encouragement throughout this program. You have seen me through some pretty steep hills and low valleys. I could not have asked for a more loving and supportive brother. To Justin A. Seyler, my reunited brother, thanks for keeping me sane through this insane process. I literally could not have done this without you. To my lab mates and other graduate students, of whom I have been blessed to cross paths within my time at the University of Denver, thank you for the knowledge you have imparted to me. I will always do my best to pay that kindness forward. To Virginia Pearl Schnur, my loving grandmother. Thank you for all the love, support, guidance, and the grit & determination you have modeled for me. Without every little thing you have done for my life I would not be where I am today. Thank you to those who have aided in the editing of this dissertation. Finally, to my loving, beautiful, supportive wife, Carolyn M. Coles-Taylor, a document of double the length of this dissertation could not fully to express what you have meant to the completion of this degree. You have been my rock, and I am excited to be yours as you embark on your own doctoral journey at the University of California, Irvine. To all of those who have profoundly impacted the trajectory of my life, I am forever grateful. Peace, Love, and Prosperity, Brandon L. Coles-Taylor iv Table of Contents Abstract ......................................................................................................................... ii Acknowledgements ....................................................................................................... iv Table of Contents ........................................................................................................... v List of Figures ............................................................................................................. vii Chapter One: Regioselectivity in Metal-Catalyzed Alkyne Annulations ...................... 1 1.1 Transition Metal-Catalyzed Annulations of Unsymmetrical Alkynes................ 1 1.1.1 Rhodium .................................................................................................. 3 You and coworkers developed a N-assisted C–H General Information ..................... 10 1.1.2. Palladium .................................................................................................. 14 1.1.3 Ruthenium .................................................................................................. 20 1.1.4 Other Transition Metals ............................................................................. 26 1.1.5 Conclusion ................................................................................................. 37 Chapter Two: The Synthesis and Reactivity of Ynol Ethers ...................................... 40 2.1 Synthesis of Ynol Ethers ................................................................................... 40 2.1.1 -Elimination ............................................................................................. 41 2.1.2 -Elimination ............................................................................................. 55 2.1.3 Oxidation of Terminal Alkynes ................................................................. 57 2.2 Reactivity of Ynol Ethers.................................................................................. 59 2.2.1 Cycloadditions of Ynol Ethers: The Utility of Ketene Surrogates ............ 60 2.2.2 Metal Migratory Insertion Across Ynol Ethers ......................................... 67 2.3 Conclusions ....................................................................................................... 71 Chapter Three: Accessing 4-Oxy-Substituted Isoquinolinones via C–H Activation and Regioselective Migratory Insertion with Electronically Biased Ynol Ethers ................... 73 3.1 Introduction ....................................................................................................... 73 3.1.1 Synthesis of Isoquinolinones via Transition Metal-Catalyzed Alkyne Annulations ............................................................................................................... 74 3.1.2 Controlling Alkyne Migratory Insertion with Electronically Biased Alkynes ..................................................................................................................... 84 3.2 Results and Discussion ..................................................................................... 86 3.2.1 Optimization of Reaction Conditions ........................................................ 86 3.2.2 Synthesis of Isoquinolinones 288 .............................................................. 88 3.2.3 Synthesis of FG-4497 Analogue ................................................................ 92 3.3 Conclusions ....................................................................................................... 94 3.4 Experimental Procedures .................................................................................. 95 v 3.4.1 Synthesis of Alkylated Ynol Ethers 287b-d............................................... 96 3.4.2 Synthesis of Ynol ethers 287e and 287i ..................................................... 98 3.4.3 General Procedure for Rhodium Catalyzed Annulations......................... 100 3.5 NMR Spectra from Chapter 3 ......................................................................... 113 Chapter Four: Access to Substituted Indenol Ethers via Carbopalladation Heck Cascades ........................................................................................................................
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