Sugar Silanes in Carbohydrate Synthesis: Applications Towards Site- Selective Glycosylation by Zachary Allen Buchan
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Sugar Silanes in Carbohydrate Synthesis: Applications Towards Site- Selective Glycosylation by Zachary Allen Buchan A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Chemistry) in The University of Michigan 2011 Doctoral Committee: Professor John Montgomery, Chair Professor Masato Koreeda Professor Edwin Vedejs Associate Professor John P. Wolfe Assistant Professor Matthew B. Soellner Dedication This dissertation is dedicated to my parents, Bruce and Catherine Buchan. Without their sacrifices, support, and love I would have never accomplished what I have been able to. I am forever grateful for everything they have done for me. ii Acknowledgements I would like to thank my advisor, Professor John Montgomery, for his guidance during my tenure in graduate school. I was fortunate to have been placed on such a stimulating research project, and to have been granted the level of independence for exploration and learning that I was. The combination of John’s mentorship, and his patience in allowing me to work independently in conjunction with a great project played an integral role in my development as a scientist. Thank you to all of the students I have had the privilege of working with during my time at the University of Michigan. These interactions have allowed me the opportunity to learn a great deal from many people, both in chemistry and in life. A special thanks to Allison Knauff, Aireal Jenkins, Wei Li and Jordan Walk for their assistance in editing early drafts of my dissertation. Thank you to my committee members for taking the time to review my dissertation and provide thought provoking conversations regarding my graduate research. Thank you to Professor Masato Koreeda, who I developed a special relationship with during my time in graduate school, through teaching and spending time in his lab I learned a great deal. Thank you to Professor John Wolfe, having the opportunity to research under his guidance provided me with training that was highly to my development as a researcher. Thank you to Professor Edwin Vedejs, I learned a great deal from his teachings, and was inspired by his knowledge and passion for organic chemistry. iii A special thanks to my family and friends who have supported me during my graduate studies. I am fortunate to have the group of people in my life that I do, and I share my successes with them. I love my family and my wife more than anything. iv Table of Contents Dedication ..................................................................................................................... ii Acknowledgements ............................................................................................................ iii List of Schemes .................................................................................................................. ix List of Tables .................................................................................................................. xiv Abstract ................................................................................................................... xv Chapter 1 Ketone Hydrosilylation with Sugar Silanes Followed by Intramolecular Aglycone Delivery ...................................................................................... 1 1.1 Introduction ................................................................................................. 1 1.1.1 Role of Carbohydrates in Nature ..................................................... 1 1.1.2 Importance of Carbohydrates in Biological Activity ...................... 3 1.2 Glycosylation Methods and Challenges ...................................................... 5 1.2.1 Glycosylation Background and Nomenclature ............................... 5 1.2.2 Challenges in Synthesizing Glycosidic Bonds ................................ 6 1.2.3 Intramolecular Aglycone Delivery .................................................. 8 1.3 Development of Sugar Silanes .................................................................. 10 1.3.1 Merging of Carbohydrate Chemistry and Transition Metal Catalysis ........................................................................................ 10 1.3.2 Synthesis of Carbohydrate-Bearing Silane Reducing Agents ....... 12 1.4 Glycosylation of Ketones .......................................................................... 15 1.4.1 Ketone Hydrosilylation Background ............................................. 15 1.4.2 Developing Conditions for Ketone Reduction by Sugar Silanes .. 16 v 1.4.3 Proposed Mechanism for Ni(0)-IMes and Cu(I)-IMes Hydrosilylation ............................................................................. 20 1.4.4 Site-Selective Glycosylation of Ketones ....................................... 22 1.5 Future Directions and Ketone Glycosylation Summary ........................... 28 1.5.1 Developing Asymmetric Ketone Reductions with Sugar Silanes . 28 1.5.2 Ketone Glycosylation in Complex Molecules .............................. 31 1.5.3 Summary of Sugar Silanes in the Glycosylation of Ketones ........ 32 Chapter 2 Dehydrogenative Silylation with Sugar Silanes: Progress Towards Streamlining the Synthesis of Disaccharides ............................................ 34 2.1 Introduction to Dehydrogenative Silylation.............................................. 34 2.1.1 Transitioning from Ketone Hydrosilylation to Dehydrogenative Silylation ....................................................................................... 34 2.1.2 Advantages of Dehydrogenative Silylation with Silanes .............. 35 2.1.3 Choosing a Dehydrogenative Silylation Catalyst ......................... 36 2.1.4 Proposed Dehydrogenative Silylation Mechanism with B(C6F5)3 and Cu-IMes.................................................................................. 37 2.2 Dehydrogenative Silylation of Alcohols with Sugar Silanes .................... 39 2.2.1 Developing Conditions with B(C6F5)3 and Sugar Silanes ............. 39 2.2.2 B(C6F5)3 Catalyzed Dehydrogenative Silylation of Alcohols ....... 41 2.2.3 Site-Selective Dehydrogenative Silylation of Hydroxyketones .... 43 2.2.4 Additional Applications of Sugar Silanes in Dehydrogenative Silylation ....................................................................................... 45 2.3 Site-Selective Glycosylation of Diols ....................................................... 47 2.3.1 Mechanistic Implications of B(C6F5)3 Catalyzed Dehydrogenative Silylation ....................................................................................... 47 2.3.2 Using Sugar Silanes for Selective Silylation of Diols .................. 49 2.3.3 Glycosylation of 4-Hydroxy Tethered Compounds ...................... 54 vi 2.3.4 Gaining Additional Insight on Site-Selective Silylation/Glycosylation of Diols ................................................. 62 2.4 Future Directions and Summary of Dehydrogenative Silylation .............. 66 2.4.1 Building Upon Selective Silylation/Glycosylation of Diols Studies ....................................................................................................... 66 2.4.2 Selective Silylation of Complex Substrates .................................. 67 2.4.3 Summary of Dehydrogenative Silylation with Sugar Silanes ....... 68 Chapter 3 Merging Aglycone Synthesis and Glycosylation by Reductive Coupling with Sugar Silanes..................................................................................... 70 3.1 Reductive Coupling Background .............................................................. 70 3.1.1 Introduction to Reductive Coupling Strategy................................ 70 3.1.2 Use of Silanes as Reducing Agents in Nickel-Catalyzed Reductive Coupling ........................................................................................ 71 3.2 Nickel-Catalyzed Reductive Coupling with Sugar Silane Reducing Agents 76 3.2.1 Development of Conditions with Sugar Silanes and Terminal Alkynes ......................................................................................... 76 3.2.2 Reductive Coupling with Internal Alkynes and Sugar Silanes ..... 83 3.2.3 Reductive Macrocyclizations with Sugar Silanes ......................... 85 3.2.4 Reductive Coupling with Sugar Silanes Using Chiral NHCs ....... 86 3.3 Glycosylation of Allylic Alcohols ............................................................ 88 3.3.1 Initial Attempts at Glycosylating Allylic Alcohols ....................... 88 3.3.2 Development of Radical Cation Glycosylation Conditions .......... 90 3.3.3 Hydrogenation Studies on Silyl-Linked Allylic Alcohols .......... 100 3.4 Summary and Future Directions ............................................................. 104 Chapter 4 Experimental Procedures and Spectral Data ........................................... 107 4.1 Chapter 1 Experimental Procedures and Spectral Data .......................... 107 4.1.1 Chapter 1 Experimental Procedures ............................................ 107 vii 4.2 Chapter 2 Experimental Procedures and Spectral Data .......................... 139 4.2.1 Chapter 2 Experimental Procedures ............................................ 139 4.3 Chapter 3 Experimental Procedures and Spectral Data .......................... 167 4.3.1 Chapter 3 Experimental Procedures ............................................ 167 References ................................................................................................................. 187 viii List of Schemes