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ABSTRACT Young, Damian Winston. Studies Toward the Total Synthesis

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ABSTRACT Young, Damian Winston. Studies Toward the Total Synthesis ABSTRACT Young, Damian Winston. Studies Toward the Total Synthesis of the Lycopodium Alkaloid Spirolucidine Using the N-Acyl-2,3-dihydro-4-pyridone as a Building Block. (Under the Direction of Daniel Lee Comins). Spirolucidine is a complex alkaloid isolated from the club moss Lycopodium lucidulum. A three fragment convergent plan for the title compound was envisioned, with each fragment being derived from a chiral N-acyl-2,3-dihydro-4-pyridone. The synthesis of the bicyclic enecarbamate referred to as zone C was investigated. The first effort centered on a tandem intramolecular Diels-Alder reaction/retro Mannich ring opening reaction to set the key stereogenic centers within zone C. A second strategy aimed to ring open the tricyclic adduct which arises from the Diels-Alder reaction through an E1cB mechanism. Finally, a third attempt was made to utilize chirality transfer as a means to implement the necessary stereochemical elements of the bicyclic scaffold. The convergent union of the key fragments of spirolucidine was modeled on a simple substrate. The directed lithiation of N-Boc-dihydropyridines was utilized to prepare model 2,5,6-trisubstituted dihydropyridones of a general type needed for the completion of the spirolucidine synthesis. STUDIES TOWARD THE TOTAL SYNTHESIS OF THE LYCOPODIUM ALKALOID SPIROLUCIDINE USING THE N-ACYL-2,3-DIHYDRO-4-PYRIDONE AS A BUILDING BLOCK By DAMIAN WINSTON YOUNG A dissertation to the Graduate Faculty of the North Carolina State University in partial fulfillment of the requirements of the Degree of Doctor of Philosophy DEPARTMENT OF CHEMISTRY Raleigh 2004 Approved by: ________________________ _________________________ Chair of Advisory Committee ________________________ _________________________ ii DEDICATION I would like to dedicate this work in loving memory of my father, the late Ronald Winston Young, and my grandmother, the late Edith Sibert Macon. Although, they are no longer with me physically, they will forever remain with me in spirit. It is through their unconditional love that I was able to develop into the person that I am today. I will continually strive to live in the exemplary ways of upbringing that they taught me. iii BIOGRAPHY The author, Damian Winston Young, was born in Savannah, Georgia on June 29, 1975 to Attorney Ronald Young and Mrs. Sherill Young. After graduating from Glynn Academy in Brunswick, Georgia, Damian successfully completed a Bachelor of Science degree in chemistry with a minor in mathematics from Howard University in Washington, D.C. Damian gained a plethora of research experience through internships, co-ops and post- undergraduate jobs. In January of 2000, Damian began his graduate studies under the direction of Professor Daniel L. Comins. In 2001, he was awarded the National Institutes of Health Pre- Doctoral Fellowship. In 2002, he was invited to join the PLU Chemistry Honor Society at North Carolina University. Upon completion of his Ph.D., he began a postdoctoral position at Harvard University under the direction of Professor Stuart L. Schreiber. iv ACKNOWLEDGEMENTS I truly believe that a person moves forward in life only as a result of those people who are placed in his life. The very dynamic span of time which will henceforth be known as “my graduate school years”, are brimming with memories of wonderful people to whom I am most indebted to. In this regard, I would like to thank Dr. Daniel Comins for his mentorship, advice, and support throughout these years. I would also like to thank my committee members, Dr. Bruce Novak, Dr. Suzanne Purrington, and Dr. Jonathan Lindsey for their helpful comments in the preparation of this dissertation. A special acknowledgement is given to Dr. Novak, who saw in me the potential to be a professor, and whose effort toward realization of this will never be forgotten. Friendships have been essential to my experience in graduate school. I would like to thank all the present and past members of the Comins research group. I would like to especially acknowledge Mr. Ibrahim Bori, Mr. Brian DeCamp, Mr. Jason Dinsmore, Ms. Florence“Flo” Fevŕier, Dr. Dimitar Gotchev, Mr. Lucas Marks, Mr. Stephen McCall, Dr. Michel Nuchols, and Dr. Bradley Wolfe. Much of what I learned throughout this experience is because of all of you. I thank you all for being my colleagues, but more importantly for being my friends. The confidence that you have in me inspires me to move forward. I would like to thank Dr. Angela Allen and Dr. Chiamaka Porter for being the sisters that I never had. I value our relationship more than you will ever know. Thank you for teaching me some very important lessons that transcend chemistry. My family has been my backbone, and I am truly blessed to have such wonderful people in my corner. To my mother, Mrs. Sherill Young, I thank you for being an extraordinary mother and my lifelong best friend. I would not be where I am today without v your love and guidance throughout my entire life. To my grandfather, Mr. Ralph Macon, you are a continual inspiration to me of what a strong man should be. To Mr. William Crosby, I thank you for the unfailing support and peace of mind that you have given me during these past five years. To Mr. Jack Hester and Mrs. Maryln Hester, I thank you for accepting me as your new son and providing me with the strong encouragement necessary to make it through these years. And finally, to my loving wife Shawna, I find it exceedingly difficult to articulate words that appropriately express my thanks for what you have done for me. The sacrifices that you have made and are making now go far beyond what most would give. Thank you for loving me enough to allow me the freedom to pursue my dreams. Truly I say that you are my friend, confidant, and soul mate, and I look happily forward to spending the rest of my life with you. vi TABLE OF CONTENTS Page LIST OF TABLES…………………………………………………………… viii LIST OF FIGURES………………………………………………………….. ix LIST OF SCHEMES………………………………………………………… x LIST OF ABBREVIATIONS AND TERMS……………………………… xv INTRODUCTION…………………………………………………………… 1 I. Preparation of 2,3-Dihydro-4-pyridones……………………. 2 1.1. Dihydropyridones Arising From Acyclic Precursors…………………………………………. 2 1.2. Dihydropyridones from Pyridine Precursors……... 8 II. Reactions of 2,3-Dihydro-4-pyridones………………………. 12 CHAPTER 1: SPIROLUCIDINE AND ITS BIOSYNTHETIC ORIGINS…………………………………………………….. 27 CHAPTER 2: TOWARDS THE TOTAL SYNTHESIS OF THE LYCOPODIUM ALKALOID SPIROLUCIDINE………... 36 I. The Synthetic Plan for Spirolucidine……………………….. 36 II. The Synthesis of Zone A…………………………………… 43 III. Progress towards the Synthesis of the Zone C Fragment of Spirolucidine………………………………………………… 47 3.1. Intramolecular Tandem Diels-Alder/Retro-Mannich Approach…………………………………………… 47 3.2. Ring Opening through an E1cb Type Elimination…. 54 3.3. Chirality Transfer Reactions………………………… 68 3.4. Other Methods of Bicycle Formation………………. 81 CHAPTER 3: MODEL STUDIES TOWARD THE CONVERGENCE OF ZONES IN SPIROLUCIDINE………………………………… 85 Introduction………………………………………………………… 85 I. Olefin Addition Olefin Regeneration Model Studies……………. 89 II. Directed Lithiations toward the Desired Model Compound…… 99 vii Page CHAPTER 4: DIRECTED METALATIONS TOWARD 2,6-DISUBSTITUTED AND 2,5,6-TRISUBSTITUTED DIHYDROPYRIDONES……………………………..... 113 I. Directed Lithiations to Form 2,6-Disubstituted- Dihydropyridones……………………………………… 113 II. Directed Lithiations to Form 2,5,6 Trisubstituted Dihydropyridones……………..……………………… 117 CONCLUSIONS…....…………………………………………………… 123 EXPERIMENTAL……………………………………………………… 125 REFERENCES…………………………………………………………… 188 viii LIST OF TABLES Page Table 1. Attempted Elimination Reaction of 145a…………………………….. 59 Table 2. Attempted Reduction of Vinyl Bromide by Diimide………………….. 66 Table 3. Attempted [2,3]-Sigmatropic Rearrangement…………………………. 76 Table 4. Electrophilic Iodination Reaction……………………………………… 103 Table 5. Substitution of C5 with Various Electrophiles…………………………. 118 Table 6. Conjugate Addition to Substrate 256 Using Various Organocopper Reagents………………………………………………………………… 119 ix LIST OF FIGURES Page Figure 1. The Dihydropyridone Family ……………………………………… 1 Figure 2. General Structure and Utility of N-Acyl-2,3-dihydro-4-pyridones… 8 Figure 3. The Versatility of N-Acyl-2,3-dihydro-4-pyridones………………. 11 Figure 4. Structure of Spirolucidine………………………………………….. 27 Figure 5. The Lucidine Family: Alkaloids of the Lycopodium Lucidulum……. 28 Figure 6. Fifty Years of Alkaloid Total Synthesis……………………………… 37 Figure 7. Rationale for Stereoselective Reduction of the C4 Carbonyl…………. 62 Figure 8. Comparison of Diimide Reductions……………………………………. 67 Figure 9. New Strategy for Producing the Zone A-B-C Model …………………… 99 x LIST OF SCHEMES Page Scheme 1. Preparation of Dihydropyridones from β-amino Esters………….. 2 Scheme 2. The Cyclization of Glycosyl Eneamines to Glycosyl Dihydropyridones………………………………………………… 3 Scheme 3. Liquid Phase Synthesis of 2,3-Dihydro-4-pyridones……………… 4 Scheme 4. The Aza Diels Alder Reaction of a Functionalized Imine…………. 5 Scheme 5. Catalytic Asymmetric Dihydropyridine Formation Using a Chiral Silver Catalyst……………………………………………………… 6 Scheme 6. Enantioselective Formal Diels Alder Reaction of Chiral Copper Complexes…………………………………………………………… 7 Scheme 7. Preparation of Racemic N-acyldihydropyridones…………………… 9 Scheme 8. Preparation of Enantiopure N-acyldihydropyridones………………… 10 Scheme 9. The Equilibration of Dihydropyridone Enolates…………………… 13 Scheme 10. Utilization of Dihydropyridones Toward the Synthesis of (+/-)-Epiuleine…………………………………………………… 14 Scheme 12. Weinreb's Application of the Dihydropyridone
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