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Title Synthetic Strategies toward Aconitine-type and Hetisine-type Diterpenoid Alkaloids

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Author Pflueger, Jason Jon

Publication Date 2016

Peer reviewed|Thesis/dissertation

eScholarship.org Powered by the California Digital Library University of California Synthetic Strategies toward Aconitine-type and Hetisine-type Diterpenoid Alkaloids

Jason Jon Pflueger

A dissertation submitted in partial satisfaction of the

requirements for the degree of

Doctor of Philosophy

Chemistry

in the

Graduate Division

of the

University of California, Berkeley

Committee in Charge:

Professor Richmond Sarpong, Chair Professor Thomas Maimone Professor Leonard Bjeldanes

Fall 2016

Abstract

Synthetic Strategies toward Aconitine-type and Hetisine-type Diterpenoid Alkaloids

Jason Jon Pflueger

Doctor of Philosophy in Chemistry

University of California, Berkeley

Professor Richmond Sarpong, Chair

Diterpenoid alkaloid natural products, isolated from plants in the Aconitum, Delphinium, Consolida, and Spiraea genera, possess complex, caged, highly oxygenated skeletons and display potent biological activities through interactions with voltage-gated ion channels. Several of these alkaloids are currently used clinically for the treatment of arrhythmia, while others act as incredibly potent neurotoxins. Until recently, there were very few successful total syntheses of any diterpenoid alkaloid natural products, a testament to the structural complexity of these molecules. We explored synthetic strategies targeting two major types of these natural products: the aconitine-type C19-diterpenoid alkaloids and the hetisine-type C20-diterpenoid alkaloids. Initial work explored Diels–Alder cycloadditions with maleic anhydride-derived dienophiles toward the eventual construction of aconitine-type diterpenoid alkaloids. We examined the selective ring-opening of these adducts with a variety of nucleophiles and utilized an ester-stabilized benzylic nucleophile to achieve C–C bond formation with complete positional selectivity. This product was rapidly elaborated to a vinyl lactone intermediate, which following amine addition and oxidation underwent a high-yielding, diastereoselective methylation reaction to install the challenging C18 carbon atom. Synthesis of the hetisine-type diterpenoid alkaloid cossonidine built off of previous work performed in the Sarpong lab. Reexamining the previously-developed route, we optimized several steps and implemented new reactions to increase the yield and reproducibility of the chemistry and reduce the overall step count. Subsequent functional group transformations involving deprotection and inversion of the C1 hydroxyl group and installation of the allylic alcohol moiety completed the first total synthesis of cossonidine. Recognizing the connections between the various diterpenoid alkaloid types, we explored ways to convert the vinyl lactone intermediate developed in our studies toward aconitine-type natural products into the hetisine-type skeleton of cossonidine. Following the introduction of an iodine atom on the aromatic ring, magnesium-halogen exchange leads to an intramolecular cyclization reaction to forge the central 6-7-6 tricycle with carbonyl groups at all three nitrogen- bearing carbon atoms following oxidation. Efforts to install the C18 methyl group and accomplish a triple reductive amination cascade to complete this second-generation total synthesis are ongoing.

TABLE OF CONTENTS

Acknowledgements ...... iii

Chapter 1. Diterpenoid Alkaloid Natural Products: Classification, Biosynthesis, Biological Activities, and Selected Syntheses ...... 1 1.1 Introduction ...... 1 1.2 Structural Classification ...... 1 1.3 Biosynthesis ...... 3 1.4 Biological Studies ...... 4 1.5 Previous Syntheses...... 4 1.5.1 Syntheses of C18- and C19-Diterpenoid Alkaloids ...... 5 1.5.2 Syntheses of Denudatine-type C20-Diterpenoid Alkaloids ...... 7 1.5.3 Syntheses of the Hetidine-type C20-Diterpenoid Alkaloid Skeleton...... 8 1.5.4 Syntheses of the Hetisine-type C20-Diterpenoid Alkaloid Nominine ...... 10 1.6 Conclusion ...... 11 1.7 References ...... 11

Chapter 2. Initial Efforts toward the Aconitine-type Skeleton: Diels–Alder Reactions with Maleic Anhydride-based Dienophiles and Subsequent Derivatization ...... 13 2.1 Introduction ...... 13 2.2 Retrosynthetic Analysis ...... 13 2.3 Diels–Alder Cycloaddition Studies...... 14 2.4 Derivatization Studies of Bicyclic Anhydride 2.5 ...... 16 2.5 Synthesis and Elaboration of a Homologated Diels–Alder Adduct ...... 17 2.6 Conclusion ...... 20 2.7 Experimental Procedures and Characterization Data ...... 20 2.8 References ...... 31

Appendix 1. NMR Spectra and Crystallography Data for Compounds Discussed in Chapter 2 ...... 33

Chapter 3. Total Synthesis of Cossonidine: A Benzyne-Insertion Route toward Hetisine- type C20-Diterpenoid Alkaloids ...... 73 3.1 Introduction ...... 73 3.2 Retrosynthesis and Previous Work toward the Heptacyclic Core of Cossonidine ...... 74 3.3 Optimization of the Initial Route to the Heptacyclic Core ...... 75 3.4 Completing the Total Synthesis of Cossonidine ...... 83 3.5 Conclusion ...... 87 3.6 Experimental Procedures and Characterization Data ...... 87 3.7 References ...... 101

Appendix 2. NMR Spectra for Compounds Discussed in Chapter 3 ...... 104

Chapter 4. Exploring a Second-Generation Synthesis of Cossonidine: A Magnesiate- Insertion Route to the 6-7-6 Tricycle ...... 129 4.1 Introduction ...... 129 4.2 Initial Studies on C–C Bond Formation to Access the 6-7-6 Tricyclic Core ...... 129 4.3 Late-Stage Iodination and Elaboration to Diketoaldehyde 4.18 ...... 133 4.4 Efforts to Elaborate Diketoaldehyde 4.18 to the Hetisine Core...... 135 4.5 Conclusion ...... 136 4.6 Experimental Procedures and Characterization Data ...... 137 4.7 References ...... 140

Appendix 3. NMR Spectra and Crystallography Data for Compounds Discussed in Chapter 4 ...... 141

Acknowledgements

First and foremost, I would like to thank my parents, Richard and Helen, for their constant support and inspiration. It is from you that I learned how to dream big, work hard, and give back more than I receive. None of this would have been possible without you. I was also lucky to have three wonderful siblings growing up, Rebecca, Bryan, and Miranda, who have my lifelong appreciation and admiration. Throughout my education, I was fortunate to have many wonderful teachers and mentors. I would specifically like to thank my high school chemistry teachers, Dr. David Ostfeld, Dr. Todd Crane, Dr. Laura Crane, and Mrs. Elizabeth Sorrentino, for sharing their passions for chemistry and education with me. Their support and encouragement was instrumental in helping me along my path of personal and professional growth. As an undergraduate at Columbia University, I was lucky to be a member of Professor Scott Snyder’s research group for over three years. My time in the Snyder lab exposed me to the real world of chemistry research, providing me with the training, experience, and confidence to pursue my own projects as a graduate student. I am very grateful to Scott and the entire Snyder group for their time, advice, and support. My deepest thanks and appreciation go out to my dissertation advisor, Professor Richmond Sarpong, for being a constant source of knowledge, ideas, and support. He has been a wonderful educator and mentor, and I will forever be deeply indebted to him. I’d also like to thank the members of my qualifying exam and dissertation committees, Professors John Hartwig, Tom Maimone, Robert Bergman, and Leonard Bjeldanes, for comments and support. Thanks also go out to the facilities personnel at Berkeley, especially Chris Canlas, Jeffrey Pelton, and Hasan Celik for NMR assistance, and Antonio DiPasquale for X-Ray crystallographic analysis. Of course, it’s impossible to survive graduate school on your own, and I am grateful to have had the opportunity to work with and learn from some of the most intelligent, talented, and helpful people I could ever ask for. Far too many people have passed through the Sarpong group for me to name here individually, but all of them helped contribute to a fantastic work environment that I consider myself lucky to have been a part of. I’d specifically like to thank Jim Newton and Ethan Fisher, who helped me get acquainted with graduate school, life in 842 Latimer Hall, and summer softball. I’ve had the honor to work closely with several stellar chemists, and I’d especially like to thank Eduardo Mercado, Jessica Kisunzu, Louis Morrill, and Kevin Kou for their time, insights, and ideas over the years. I’d also like to thank Paul Leger, Kyle Owens, Rebecca Johnson, Brian Wang, Nicolle Doering, Beryl Li, and Melissa Hardy for helpful comments on this dissertation and for being wonderful friends and coworkers. Perhaps less obvious, but in my eyes no less important, are all the friends who helped me maintain at least a modicum of sanity throughout my time in graduate school. Whether we were getting lunch together, playing board games, going out for trivia, or participating in a puzzle hunt, you’ve helped generate some of my fondest memories from these past few years. While many people have joined me in these pursuits over the years, I’d particularly like to acknowledge the most consistent participants, who have spent way more hours than I can count recalling obscure trivia, rolling dice, or tackling a stubborn puzzle by my side. So thank you Max Horlbeck, Darienne Myers, Katie Klymko, Grace Chan, Dave Sukhdeo, Cheri Ackerman, Debra McCaffrey, Paul Leger, Grace Carroll, Kyle Owens, Rebecca Johnson, Brian Wang, Nicolle Doering, and Beryl Li for all the adventures! I’m looking forward to many more to come!

iii

Chapter 1. Diterpenoid Alkaloid Natural Products: Classification, Biosynthesis, Biological Activities, and Selected Syntheses

1.1 Introduction The diterpenoid alkaloids are a collection of over 1,200 small molecules isolated primarily from plants in the Aconitum, Delphinium, Consolida, and Spiraea genera. While these flowering plants are notorious for their poisonous nature, they have long seen use, following proper preparation, as herbal remedies, possessing anti-inflammatory, analgesic, and antiarrhythmic properties. The diterpenoid alkaloids have been identified as the active ingredients that give these plants their observed bioactivities, primarily through their interactions with voltage-gated ion channels. Taken together with the complex, caged structural features that characterize these natural products, the diterpenoid alkaloids have served as tantalizing targets for total synthesis by our research group and others. This chapter will introduce the diterpenoid alkaloids, describing their structure and broad classification, as well as their presumed biosynthesis. Details on the bioactivity studies of these molecules will be presented, with a focus on their interactions with voltage-gated ion channels. Finally, a summary of previous syntheses of diterpenoid alkaloid natural products will be discussed.

1.2 Structural Classification The diterpenoid alkaloids are broadly classified based on the number of carbon atoms 1 that comprise their core skeletons into the C18-, C19-, and C20-diterpenoid alkaloids. Each of these groups has been further subdivided based on key conserved structural features.

The C18-diterpenoid alkaloids (Figure 1-1) are the smallest of the three main groups of 1a diterpenoid alkaloids, with only 78 molecules known as of 2009. The C18-diterpenoid alkaloids can be subdivided into two very similar types: the lappaconitine-type and the ranaconitine-type, the latter of which contains additional oxygenation at C7.

Figure 1-1. C18-diterpenoid alkaloid types

The C19-diterpenoid alkaloids (Figure 1-2) are a much larger group of molecules, with 1b 672 compounds characterized as of 2008. Structurally similar to the C18-diterpenoid alkaloids, the C19-diterpenoid alkaloids bear an additional carbon atom at the piperidine ring junction position. Because of the greater number and variety of known compounds, the C19-diterpenoid alkaloids are subdivided into 6 different types. The aconitine-type and lycoctonine-type alkaloids, which are the C19 analogues of the two C18-diterpenoid alkaloid types, comprise nearly all of the known C19-diterpenoid alkaloids. The other four subdivisions are the pyro-type, lactone-type, 7,17-seco-type, and rearranged-type alkaloids, which collectively contain the remaining 37 alkaloids.

Figure 1-2. C19-diterpenoid alkaloid types

The C20-diterpenoid alkaloids (Figure 1-3) are the final group of diterpenoid alkaloids, 1c,d with 376 compounds identified as of 2010. The C20-diterpenoid alkaloids display a greater variety in structure, subdivided into 16 types, with a much more even distribution than that displayed by the C19-diterpenoid alkaloids in which nearly all members belong to one of 2 closely related types. These 16 groups are the atisine-type, denudatine-type, hetidine-type, hetisine-type, cardionidine-type, albovionitine-type, vakognavine-type, veatchine-type, napelline-type, anopterine-type, delnudine-type, kusnezoline-type, actaline-type, racemulosine- type, arcutine-type, and tricalysiamide-type diterpenoid alkaloids. Perhaps most notably, while virtually all of the C18- and C19-diterpenoid alkaloids possess a [3.2.1]bicycle in the Eastern half of these representations, the vast majority of the C20-diterpenoid alkaloids contain a [2.2.2]bicycle.

Figure 1-3. C20-diterpenoid alkaloid types

1.3 Biosynthesis Biosynthetically, the diterpenoid alkaloids are derived from geranyl geranyl pyrophosphate (GGPP, 1.1, Scheme 1-1). An enzyme-catalyzed cyclization provides ent-copalyl pyrophosphate (ent-CPP, 1.2), which undergoes further cyclization, a hydride shift, and Wagner– Meerwein rearrangement to provide the ent-atisane diterpene skeleton (1.7). From the atisane skeleton, amination leads to the atisine skeleton (1.8), the branching point for the biosynthesis of the rest of the diterpenoid alkaloids.1,2

Scheme 1-1. Biosynthesis of the atisine skeleton

From the atisine skeleton, formation of a C14–C20 bond (see Scheme 1-2 for numbering) gives rise to the hetidine skeleton, and subsequent N–C6 bond formation affords the hetisines. Alternatively, a C7–C20 bond formation on the atisine core provides the denudatine skeleton, which can undergo a Wagner–Meerwein rearrangement from the [2.2.2]bicycle to the [3.2.1]bicycle to yield the C19 and C18 skeletons after successive C–C bond cleavage events. A series of related alkyl shifts and C–C bond forming events can be imagined to lead to the other, albeit less prominent, members of the diterpenoid alkaloids.1,2

Scheme 1-2. Biosynthetic proposal for the major diterpenoid alkaloid types

1.4 Biological Studies Physiologically, the observed activities of the diterpenoid alkaloids are believed to derive from their interactions with voltage-gated ion channels, primarily sodium and potassium channels.3 While much is still not understood about the nature and exact location of binding by the diterpenoid alkaloids, they are believed to bind with high specificity to a poorly-defined site 2 on the sodium ion channel. Despite their overall structural similarities, many diterpenoid alkaloids show differing, and in some cases even inverse, activities with ion channels. One of the most notable examples is when comparing the activity of aconitine (1.9, Figure 1-4) to that of lappaconitine (1.10). While aconitine acts as a sodium channel activator, lappaconitine functions as a sodium channel blocker, even though they are believed to bind in the same pocket and possess many similar structural features.4 Furthermore, talatisamine (1.11), another related alkaloid, actually binds to potassium channels over sodium channels, acting as a blocker.5 Guan- fu base A (1.12), a C20-diterpenoid alkaloid, has also been shown to act as a sodium-channel blocker.6

Figure 1-4. Selected diterpenoid alkaloids and their observed ion channel interactions

Physiologically, these interactions lead to a number of observed effects. Aconitine (1.9), by virtue of its function as a sodium channel activator, is one of the most powerful neurotoxins to have been identified, with as little as 2 mg being potentially fatal to a human being.7 Aconitine is also one of the primary components leading to the toxicity of the aconite plants. Other diterpenoid alkaloids, however, demonstrate anti-inflammatory, analgesic, and antiarrhythmic activities, with both lappaconitine (1.10) and guan-fu base A (1.12) currently used clinically in China for the treatment of arrhythmia.1 While some studies have also demonstrated potential anticancer, insect repellant, and antifeedant properties, these effects are not as well understood or as thoroughly investigated.1

1.5 Previous Syntheses Given the structural complexity and therapeutic potential of this class of natural products, a number of research groups have pursued the total syntheses of diterpenoid alkaloids.8 This section will review the major successful syntheses of diterpenoid alkaloids, with a focus on recent work and syntheses relevant to the work discussed in subsequent chapters of this dissertation.

1.5.1 Syntheses of C18- and C19-Diterpenoid Alkaloids One of the pioneers in the structural elucidation and synthesis of diterpenoid alkaloid natural products was Karel Wiesner. Throughout the 1970s, the Wiesner lab completed the syntheses of several diterpenoid alkaloids, evolving their strategies over multiple generations.9 In their pioneering synthesis of talatisamine (1.11, Scheme 1-3), Wiesner employed a biomimetic Wagner–Meerwein rearrangement as a key transformation to convert the [2.2.2]atisine-type skeleton into the [3.2.1]aconitine-type core.10 Starting from an advanced atisine-type skeleton (1.13), Wiesner was able to advance this compound to tosylate 1.14 in five steps. Heating this compound in a 1:1 mixture of DMSO and tetramethylguanidine led to the desired Wagner– Meerwein rearrangement to provide the desired [3.2.1]bicycle (1.15) in 40% yield. Four subsequent steps completed the total synthesis of talatisamine (1.11).

Scheme 1-3. Wiesner’s total synthesis of talatisamine

Following this work by Wiesner in the 1970s, the syntheses of diterpenoid alkaloid natural products lay relatively dormant for over 30 years. With regard to the [3.2.1]bicycle- bearing C18- and C19-diterpenoid alkaloids, the next total synthesis did not come until 2013, when Gin published their synthesis of the lappaconitine-type alkaloid neofinaconitine (1.21, 11 Scheme 1-4). After synthesizing dienophile 1.16 and diene 1.17, a SnCl4-mediated Diels– Alder reaction proceeded in 87% yield to provide Diels–Alder adduct 1.18. After oxidative cleavage of the exocyclic methylene and elimination of the bromine atom, a Mannich-type N- acylimminium cyclization mediated by Tf2NH furnished the C11–C17 bond, which after allylic oxidation and elimination provided 1.19. At this stage, an alkyl radical was generated from the bromide with Bu3SnH and AIBN, which underwent a conjugate addition into the enone, forging the C7–C8 bond in 1.20, completing the hexacyclic core of the aconitine-type diterpenoid alkaloids. The total synthesis of neofinaconitine (1.21) was completed in 11 additional steps.

Scheme 1-4. Gin’s total synthesis of neofinaconitine

Shortly thereafter, the Sarpong group published their syntheses of the lappaconitine-type C18-diterpenoid alkaloid weisaconitine D (1.28) and the aconitine-type C19-diterpenoid alkaloid liljestrandinine (1.30) through a unified approach guided by network analysis (Scheme 1-5).12 The synthesis began with a Diels–Alder reaction between diene 1.22 and dienophile 1.23, which is followed by reduction, vinyl nitrile formation, and Rh-catalyzed conjugate addition to provide 1.24. A series of functional group manipulations at that stage afforded carbamate 1.25. Mesylate formation and displacement with the carbamate nitrogen smoothly installed the piperidine ring, after which MOM cleavage and oxidative dearomatization afforded dienone 1.26. Diels–Alder cycloaddition followed by functional group manipulation about the [2.2.2]bicycle provided 1.27. This substrate then underwent a Wagner–Meerwein rearrangement analogous to that reported by Wiesner to access the [3.2.1]bicycle, which was advanced to the C18-diterpenoid alkaloid weisaconitine D (1.28) in 8 additional steps.

Scheme 1-5. Sarpong’s total synthesis of weisaconitine D

Accessing members of the C19-diterpenoid alkaloids necessitates installation of the C18 carbon atom, which was also demonstrated by the Sarpong lab (Scheme 1-6). From carbamate 1.25, oxidation to the aldehyde was followed by an aldol-Cannizzaro reaction and mesylation to afford germinal bis-mesylate 1.29. Piperidine formation proceeded stereoselectively followed by methoxide displacement of the mesylate, which could be advanced to the C19-diterpenoid alkaloid liljestrandinine (1.30) using similar chemistry to that discussed above.12

Scheme 1-6. Sarpong’s total synthesis of liljestrandinine

1.5.2 Syntheses of Denudatine-type C20-Diterpenoid Alkaloids The following year, the Sarpong group reported application of this same synthetic strategy to access the denudatine-type C20-diterpenoid alkaloids cochlearenine (1.33), N-ethyl- 1α-hydroxy-17-veratroyldictyzine (1.34), and paniculamine (1.35, Scheme 1-7).13 Using bismesylate 1.29 as their point of divergence, piperidine formation was followed this time by reductive cleavage of the mesylate group, and then MOM cleavage, oxidative dearomatization, and Diels–Alder cycloaddition to yield [2.2.2]bicycle 1.31, with the C18 methyl group installed. Wittig reaction, ketal hydrolysis, and Weitz–Scheffer epoxidation afforded epoxyketone 1.32, which could be advanced to all three denudatine-type natural products in short order.

Scheme 1-7. Sarpong’s total synthesis of denudatine-type diterpenoid alkaloids

The only other denudatine-type diterpenoid alkaloid to succumb to total synthesis is lepenine (1.39), synthesized by the Fukuyama lab in 2014 (Scheme 1-8).14 Their route begins with the synthesis of triene 1.36, which undergoes a Diels–Alder reaction and further elaboration to afford ketoaldehyde 1.37. A Pd-catalyzed Alloc-deprotection/condensation/Mannich reaction then forges the azabicycle which can be elaborated to dienone 1.38. A Diels–Alder reaction with ethylene forms the [2.2.2]bicycle, which can be elaborated in 8 subsequent operations to the natural product, lepenine (1.39).

Scheme 1-8. Fukuyama’s total synthesis of lepenine

1.5.3 Syntheses of the Hetidine-type C20-Diterpenoid Alkaloid Skeleton The third major group of related diterpenoid alkaloid types (after the C18/C19 and the denudatine-type diterpenoid alkaloids) are the atisine-, hetidine-, and hetisine-type C20- diterpenoid alkaloids. While there have been several syntheses of atisine-type alkaloids by Wiesner15 and more recently by Fukumoto16 and Wang,17 syntheses of the hetidine and hetisine cores have proven much more elusive.18 While no hetidine-type natural products have been synthesized to date, the Sarpong group was the first to disclose a route to access the hetidine-type skeleton (Scheme 1-9).19 This route took advantage of a gallium-catalyzed cycloisomerization reaction of indenylalkyne 1.40 to forge the central 6-7-6 tricycle of these natural products, which after elaboration provided aryl ketone 1.41. A Claisen rearrangement was then employed to install the allyl group after which nitrile reduction, Boc-protection, and intramolecular substitution reactions were carried out to provide piperidine 1.42. An oxidative dearomatization of the arene was intercepted by the Boc protecting group, leading to 1.43, which was subjected to an oxidative cleavage of the vinyl group, Michael addition, 1,4-enone reduction, and aldol reaction to provide 1.44, completing the hetidine-type core. Seven additional steps afforded dihydronavirine (1.45), although conditions to oxidize the amine to the requisite imine, in order to complete the natural product navirine, could not be identified.

Scheme 1-9. Sarpong’s synthesis of the hetidine skeleton

The Baran lab recently reported a synthesis of the hetidine-type skeleton, employing C–H activation chemistry to directly forge the C14–C20 bond (Scheme 1-10).20 Starting from (–)- steviol (1.46), the carboxylic acid moiety was converted into a phosphoramidate, followed by a fragmentation/aldol cyclization/acetylation sequence to afford phosphoramidate 1.47. At this stage, a Suárez C–H activation reaction selectively introduced an iodine atom at C20 and oxidized the nitrogen to the imine oxidation state. This compound was treated with allylamine, which facilitated an isomerization/Mannich cyclization cascade, providing the hetidine skeleton, secondary amine 1.48. The Baran lab also attempted to convert the hetidine core into the hetisine skeleton (1.49) through a subsequent C–H activation at C6, but despite numerous investigations into an HLF reaction, Suárez conditions, or additional directing groups, they were unable to realize this transformation.

Scheme 1-10. Baran’s synthesis of the hetidine skeleton

In late 2016, the groups of Qin and Wang reported a bioinspired approach to the hetidine skeleton (Scheme 1-11).21 The synthesis began with the coupling of iodide 1.50 and dithiane 1.51 through lithiation of the dithiane and substitution onto alkyl iodide 1.50 to provide 1.52. An oxidative dearomatization/Diels–Alder reaction followed by samarium diiodide cleavage of the two methoxy groups provided atisine-core compound 1.53. A series of functional group manipulations provided 1.54, which underwent intramolecular aminal formation followed by intramolecular aza-Prins cyclization to afford the hetidine-skeleton compound 1.55.

Scheme 1-11. Qin and Wang’s synthesis of the hetidine skeleton

1.5.4 Syntheses of the Hetisine-type C20-Diterpenoid Alkaloid Nominine The first successful synthesis of a hetisine-type diterpenoid alkaloid was the total synthesis of nominine (1.61) by Muratake and Natsume in 2004 (Scheme 1-12).22 They began with aldehyde 1.56, which underwent α-arylation followed by a series of functional group manipulations and cyclizations to afford nitrile 1.57. Reduction and subsequent cyclization of the cyano nitrogen atom forged the N–C6 bond, followed by a series of functional group manipulations to provide alkyne 1.58. Treatment of this alkyne with Bu3SnH and AIBN led to a radical cyclization, assembling the [2.2.2]bicycle in 1.59. Conversion of the primary alcohol to a bromine followed by allylic oxygenation affords enone 1.60, which undergoes 1,2-reduction followed by intramolecular substitution mediated by SOCl2 to afford nominine (1.61).

Scheme 1-12. Muratake and Natsume’s total synthesis of nominine

Just 2 years later, in 2006, Gin published an elegant, 15-step total synthesis of nominine (Scheme 1-13).23 The synthesis began with a Staudinger–aza-Wittig reaction between aldehyde 1.62 and azide 1.63 to provide a secondary amine that cyclized to 4-oxidoisoquinolinium betaine 1.64. Upon heating, this substrate undergoes an intramolecular 1,3-dipolar cycloaddition to afford 1.65, albeit as the minor component of a 1:3.6 mixture. Gratifyingly, this cycloaddition was found to be reversible, and the major component can be isolated and resubjected to the reaction conditions to generate more of the desired compound. Reductive cleavage of the ketone carbonyl followed by DIBAL reduction of the nitrile and subsequent Wittig methylenation afforded vinyl arene 1.66. At this stage a Birch reduction followed by a pyrrolidine-mediated Diels–Alder reaction forged the [2.2.2] bicycle, which after Wittig methylenation of the resultant ketone and allylic oxygenation with selenium dioxide, afforded nominine (1.61) in only 15 steps.

Scheme 1-13. Gin’s total synthesis of nominine

While this initial synthesis was racemic, the Gin lab was eventually able to render the synthesis asymmetric through an enantioselective conjugate addition of 1.67 mediated by a chiral NHC catalyst to provide vinyl triflate 1.68 (Scheme 1-14). This compound could be converted into vinyl nitrile 1.62 in two subsequent steps, the stereocenter of which dictates the relative stereochemistry of the rest of the operations, completing the first enantioselective synthesis of a hetisine-type diterpenoid alkaloid.24

Scheme 1-14. Gin’s enantioselective synthesis of vinyl nitrile 1.62

1.6 Conclusion Efforts toward the total synthesis of diterpenoid alkaloid natural products are rapidly growing. In fact, the majority of the syntheses discussed were published during the same time period as the work discussed in this dissertation. At the outset of the project discussed herein, the true state-of-the-art syntheses in the field were the work of Wiesner on the C18- and C19- diterpenoid alkaloids, and the synthesis of nominine by Gin. It was in this relative dearth of successful strategies for diterpenoid alkaloid total synthesis that this work was conceived. Initial work was directed toward the synthesis of the C18- and C19-diterpenoid alkaloid cores, which will be discussed in Chapter 2. Chapters 3 and 4 will detail significant advances toward the synthesis of hetisine-type C20-diterpenoid alkaloids, culminating in a total synthesis of a more highly- oxygenated hetisine-type diterpenoid alkaloid, cossonidine.

1.7 References (1) (a) Wang, F.-P.; Chen, Q.-H.; Liang, X.-T. In The Alkaloids: Chemistry and Biology; Cordell, G. A., Ed.; Elsevier Science: New York, 2009; Vol. 67; pp 1-78. (b) Wang, F.-P.; Chen, Q.-H. In The Alkaloids: Chemistry and Biology; Cordell, G. A., Ed.; Elsevier Science: New York, 2010; Vol. 69; pp 1-577. (c) Wang, F.-P.; Liang, X.-T. In The Alkaloids: Chemistry and Biology; Cordell, G. A., Ed.; Elsevier Science: New York, 2002; Vol. 59; pp 1-280. (d) Wang, F.-P.; Chen, Q.-H.; Liu, X.-Y. Nat. Prod. Rep. 2010, 27, 529-570. (2) Cherney, E. C.; Baran, P. S. Isr. J. Chem. 2011, 51, 391-405. (3) Catterall, W. A.; Cestèle, S.; Yarov-Yarovoy, V.; Yu, F. H.; Konoki, K.; Scheuer, T.; Toxicon 2007, 49, 124-141. (4) Tikhonov, D. B.; Zhorov, B. S. FEBS Letters 2005, 579, 4207-4212. (5) Song, M.-K.; Liu, H.; Jiang, J.-L.; Yue, J.-M.; Hu, G.-Y.; Chen, H.-Z. Neuroscience 2008, 155, 469-475. (6) Jin, S.-S.; Guo, Q.; Xu, J.; Yu, P.; Liu, J.-H.; Tang, Y.-Q. Chin. J. Nat. Med. 2015, 13, 361- 367. (7) Chan, T. Y. K. Clinical Toxicology 2009, 47, 279-285. (8) Liu, X.-Y.; Qin, Y. Asian J. Org. Chem. 2015, 4, 1010-1019. (9) Wiesner, K. Pure Appl. Chem. 1975, 41, 93-112. (10) Wiesner, K.; Tsai, T. Y. R.; Huber, K.; Bolton, S. E. J. Am. Chem. Soc. 1974, 96, 4490- 4492.

(11) Shi, Y.; Wilmot, J. T.; Nordstrøm, L. U.; Tan, D. S.; Gin, D. Y. J. Am. Chem. Soc. 2013, 135, 14313-14320. (12) Marth, C. J.; Gallego, G. M.; Lee, J. C.; Lebold, T. P.; Kulyk, S.; Kou, K. G. M.; Qin, J.; Lilien, R.; Sarpong, R. Nature 2015, 528, 493-498. (13) Kou, K. G. M.; Li, B. X.; Lee, J. C.; Gallego, G. M.; Lebold, T. P.; DiPasquale, A.; Sarpong, R. J. Am. Chem. Soc. 2016, 138, 10830-10833. (14) Nishiyama, Y.; Han-ya, Y.; Yokoshima, S.; Fukuyama, T. J. Am. Chem. Soc. 2014, 136, 6598-6601. (15) Guthrie, R. W.; Valenta, Z.; Wiesner, K. Tetrahedron Lett. 1966, 38, 4645-4654. (16) Ihara, M.; Suzuki, M.; Fukumoto, K.; Kametani, T.; Kabuto, C. J. Am. Chem. Soc. 1988, 110, 1963-1964. (17) Liu, X.-Y.; Cheng, H.; Li, X.-H.; Chen, Q.-H.; Xu, L.; Wang, F.-P. Org. Biomol. Chem. 2012, 10, 1411-1417. (18) Hamlin, A. M.; Kisunzu, J. K.; Sarpong, R. Org. Biomol. Chem. 2014, 12, 1846-1860. (19) Hamlin, A. M.; Lapointe, D.; Owens, K.; Sarpong, R. J. Org. Chem. 2014, 79, 6783-6800. (20) Cherney, E. C.; Lopchuk, J. M.; Green, J. C.; Baran, P. S. J. Am. Chem. Soc. 2014, 136, 12592-12595. (21) Li, X.-H.; Zhu, M.; Wang, Z.-X.; Liu, X.-Y.; Song, H.; Zhang, D.; Wang, F.-P.; Qin, Y. Angew. Chem. Int. Ed. 2016, 55, 15667-15671. (22) Muratake, H.; Natsume, M. Angew. Chem. Int. Ed. 2004, 43, 4646-4649. (23) Peese, K. M.; Gin, D. Y. J. Am. Chem. Soc. 2006, 128, 8734-8735. (24) Peese, K. M.; Gin, D. Y. Chem. Eur. J. 2008, 14, 1654-1665.

Chapter 2. Initial Efforts toward the Aconitine-type Skeleton: Diels–Alder Reactions with Maleic Anhydride-based Dienophiles and Subsequent Derivatization

2.1 Introduction In the fall of 2011, with the Wiesner lab’s total synthesis of talatisamine (2.1, Figure 2-1) standing as the only successful total synthesis of an aconitine-type diterpenoid alkaloid,1 we began a concerted effort to develop a novel and rapid approach to the synthesis of these complex natural products. Given the potent and selective bioactivities shown by the parent molecule aconitine (2.2), along with the complex pattern of oxygenation about the carbon skeleton, this molecule was chosen as the ultimate goal of this project.2 We sought to develop a rapid synthesis that would provide access to several natural products of this type. Furthermore, the synthesis of unnatural derivatives would allow us to further assess the therapeutic potential of these compounds as well as initiate studies to better understand the specifics of ion channel binding of these alkaloids.

Figure 2-1. Talatisamine and aconitine

2.2 Retrosynthetic Analysis Retrosynthetically, we sought to complete the skeleton of aconitine (2.2) by directly forging the [3.2.1]bicycle late-stage, utilizing a meta-photocycloaddition between the aromatic ring and vinyl group in 2.3 (Scheme 2-1). This photocycloaddition reaction, popularized by the Wender lab in their syntheses of cedrene and related molecules, has the potential to rapidly assemble the core skeleton of these natural products.3 We envisioned photocycloaddition precursor 2.3 could arise via lactam formation and Mannich reaction on 2.4, forging the azabicycle. This densely-substituted cyclohexene ring was expected to be generated through functionalization of bicyclic anhydride 2.5, which could be accessed through a Diels–Alder cycloaddition from diene 2.6 and dienophile 2.7.

Scheme 2-1. Retrosynthetic analysis of aconitine

2.3 Diels–Alder Cycloaddition Studies At the outset of this project, we set out to explore the utility of maleic anhydride-derived dienophiles in the Diels–Alder cycloaddition and subsequent functionalization reactions. Not only are maleic anhydrides inherently reactive dienophiles, the resulting cycloadducts offer the potential for rapid and selective functionalization reactions.4 As illustrated in Scheme 2-2, a wide range of nucleophiles can be added to these cyclic anhydrides. If positional selectivity can be controlled, these reactions provide access to diverse 1,2-bisfunctionalized substrates, which can be used for further derivatization reactions. In this way, a series of acids, esters, thioesters, amides, lactones, ketones, and alcohols can be selectively generated, greatly expanding the synthetic utility of these cycloadducts.

Scheme 2-2. Divergent reactivity of cyclic anhydrides

Our synthetic studies began with the preparation of diene 2.6. Building on published work,5 our group was able to optimize the synthesis of this diene starting from commercially available 1,4-butynediol (2.15, Scheme 2-3). Bismethylation with dimethylsulfate followed by a zipper elimination reaction with sodium amide affords enyne 2.16. Deprotonation of the alkyne followed by addition into paraformaldehyde and selective alkyne reduction yields diene 2.17, which is silyl protected with TBSCl to afford diene 2.6.

Scheme 2-3. Synthesis of diene 2.6

We next examined the synthesis of the known dienophiles (carbomethoxy)maleic anhydride (CMA, 2.21, Scheme 2-4)6 and (benzyloxymethylene)maleic anhydride (BMA, 2.7).7 First reported by Hall and coworkers in 1982, the synthesis of CMA (2.21) begins with the

14 alkylation of dimethyl malonate (2.18) with methyl bromoacetate (2.19). Subsequent bromination and elimination yields 1,1,2-tricarbomethoxyethylene (2.20), which was heated neat in the presence of phosphorous pentoxide to facilitate cyclization, providing CMA (2.21). Wood and coworkers reported the first synthesis of BMA (2.7) in 2002, starting from propargyl alcohol (2.22). Benzyl protection affords 2.23, which was subjected to a palladium-catalyzed dicarbonylation reaction to provide diester 2.24. Saponification of this diester with sodium hydroxide followed by dehydration with acetic anhydride affords BMA (2.7).

Scheme 2-4. Synthesis of dienophiles CMA and BMA

With the diene and both dienophiles in hand, we began exploring the Diels–Alder reaction (Scheme 2-5). The reaction of CMA (2.21) with diene 2.6 proceeded extremely rapidly, even at room temperature, to afford Diels–Alder adduct 2.25, albeit in only 12% isolated yield. While BMA (2.7) was not quite as reactive, heating a concentrated mixture (1.8 M) of BMA and diene 2.6 in benzene at 40 °C for 12 h provided the desired Diels–Alder adduct (2.5) in 94% yield as a single diastereomer. Furthermore, the regio- and stereochemistry of this adduct was confirmed by X-ray crystallography. Given the increased yield of this reaction and the presumed greater stability and chemoselectivity the benzyl ether substituent would afford over the methyl ester, we opted to use BMA Diels–Alder adduct 2.5 for our subsequent derivatization studies.

Scheme 2-5. Diels–Alder reactions of CMA and BMA with diene 2.6

2.4 Derivatization Studies of Bicyclic Anhydride 2.5 Starting from Diels–Alder adduct 2.5, we explored the nucleophilic addition of a number of reagents (Scheme 2-6). Addition of most nucleophiles proceeded with complete positional selectivity for the less hindered carbonyl. Thus, cyclohexylamine could be added with complete selectivity to open the cyclic anhydride, the resultant acid of which was converted into methyl ester 2.26 for isolation and characterization purposes. We could also achieve addition of methanol into the less hindered carbonyl, and converted the resultant acid into cyclohexyl amide 2.27, demonstrating that we could invert the substitution pattern about the ring by changing the order of functionalization. Under acidic conditions, we observed cleavage of the silyl enol ether, the product of which spontaneously opened the anhydride to provide bicyclic lactone 2.28 after esterification. The only change to the observed selectivity pattern was the addition of sodium borohydride, which added with high selectivity to the more hindered carbonyl, providing lactone 2.29, possibly as a result of the benzyl ether acting as a directing group for the reducing agent. Turning to 3-methoxybenzyl Grignard, however, we were unable to observe any appreciable amount of ketone 2.30, despite exploring a range of temperatures, molar ratios, and additives.

Scheme 2-6. Functionalization of bicyclic anhydride 2.5

Given the challenges encountered in the direct addition of benzyl Grignard reagents, we began exploring the use of more stabilized benzyl nucleophiles, starting with methyl ester 2.31, readily available in one step from 3-methoxyphenylacetic acid.8 Following deprotonation with LiHMDS, the resultant enolate underwent smooth addition to Diels–Alder adduct 2.5 to provide 2.32 (Scheme 2-7). Upon treatment of this substrate with HCl in MeOH, TBS cleavage followed by intramolecular acetal formation was observed to generate 2.33, in which the acetal moiety serves as an internal protecting group for the more reactive hydroxyl groups. Exploring the further derivatization of this substrate, we found that we could achieve a one-pot alkene reduction/benzyl ether cleavage to provide 2.34, which was subjected to a Ley oxidation9 to

16 afford aldehyde 2.35. We next explored a number of olefination reactions to achieve methylenation of the aldehyde carbonyl to provide vinyl lactone 2.36, including the Wittig reaction, Lebel olefination,10 Julia olefination,11 and use of the Tebbe12 and Lombardo13 reagents. Unfortunately, we were unable to identify conditions to achieve the desired methylenation.

Scheme 2-7. Elaboration of bicyclic anhydride 2.5

2.5 Synthesis and Elaboration of a Homologated Diels–Alder Adduct Given our struggles in implementing a methylenation reaction on aldehyde 2.35, we elected instead to pursue an elimination reaction from the homologated primary alcohol. This necessitated the synthesis of a homologated version of our BMA dienophile, which could be readily accessed via the same route, starting with 3-butyn-1-ol (2.37, Scheme 2-8).

Scheme 2-8. Synthesis of homologated dienophile 2.40

Heating dienophile 2.40 with diene 2.6 in refluxing toluene for 24 hours cleanly afforded Diels–Alder adduct 2.41 as a single diastereomer in 72% yield (Scheme 2-9). Addition of stabilized benzyl nucleophile 2.31 followed by treatment with HCl provided tricyclic acetal 2.42 in 75% yield over 2 steps as a roughly 1:1 mixture of diastereomers. Upon exploration of Krapcho-type conditions for the cleavage and decarboxylation of the methyl ether, we discovered that heating a mixture of 2.42 and lithium chloride in 9:1 DMF/H2O at 150 °C for 4 days provided 2.43 in 86% yield.14 Performing this reaction in a microwave reactor at 225 °C dramatically reduced the reaction time to only 30 min, with no loss in yield. A subsequent one- pot hydrogenation/hydrogenolysis reaction with H2 and Pd/C facilitated reduction of the alkene group and benzyl ether cleavage to provide primary alcohol 2.44. Upon exploration of several conditions to promote the elimination of the primary alcohol, we found that we could achieve a one-pot Grieco elimination to afford vinyl lactone 2.45 in 95% yield.15 This 5-step sequence to

17 convert Diels–Alder adduct 2.41 to vinyl lactone 2.45 proceeds in 52% overall yield and can be performed on gram-scale.

Scheme 2-9. Synthesis of vinyl lactone 2.45

With vinyl lactone 2.45 in hand, we next turned our attention to opening the lactone- acetal moiety that had served as a critical internal protecting group. We sought to use this opportunity to introduce the nitrogen atom and began investigating the addition of amine nucleophiles into vinyl lactone 2.45. After exploring several conditions for lactam formation, we found that simply heating 2.45 in a 70% solution of ethylamine in water with THF co-solvent afforded lactam 2.46 in 71% yield, the structure of which was confirmed by X-ray crystallography (Scheme 2-10).

Scheme 2-10. Ethylamine addition into vinyl lactone 2.45

With the confirmation of lactam 2.45, we sought to take advantage of this compound to install the C18 carbon atom present in all the C19- and also the C20-diterpenoid alkaloids. While aconitine possesses a methoxy-substituted carbon at this position, we began by exploring the installation of a methyl group, which had proven to be a challenging transformation in alternate routes simultaneously being explored by our group. Oxidation of 2.45 with IBX led to the

18 formation of lactone 2.47 in 84% yield,16 which smoothly underwent methylation following deprotonation with KOtBu to afford 2.48 in 83% yield (Scheme 2-11).

Scheme 2-11. Installation of the C18 carbon atom

With a smooth and high-yielding procedure for the diastereoselective incorporation of the C18 carbon atom, we next turned our attention to the construction of the aconitine-type azabicycle. Our goal was to achieve a formal reductive ring-opening of the lactone to afford amine 2.50, which following intramolecular transamidation would afford keto-lactam 2.51 (Scheme 2-12). While we were never able to achieve a nucleophilic ring-opening of the lactone, reduction with lithium borohydride did provide access to lactol 2.49. From this substrate, we explored reductive amination conditions to access amine 2.50 without success. We also looked into further reduction to the corresponding primary alcohol, which we could convert to the desired amine in subsequent steps, but complete reduction proved challenging and was often accompanied by decomposition. Ultimately, we were unable to find a way to cleanly and productively advance 2.48, and given other successes in our research group exploring an alternate route to access these cores, this project was suspended.

Scheme 2-12. Elaboration of methylated lactam 2.48

2.6 Conclusion With the total synthesis of aconitine-type diterpenoid alkaloids as our inspiration, we investigated the Diels–Alder reaction and subsequent derivatization of maleic anhydride-derived dienophiles. These studies ultimately led to a rapid and scalable synthesis of vinyl lactone 2.45, which possesses key functional groups for the eventual synthesis of various diterpenoid alkaloid natural products. While we were able to install the nitrogen atom as well as achieve a high- yielding and diastereoselective methylation to incorporate the C18 carbon atom, we were unable to productively advance these compounds to diterpenoid alkaloid cores. Simultaneously in the Sarpong group, a related route was achieving greater success in forging the central core of these and other diterpenoid alkaloids.17 With the graduation of the lead researcher on one of these projects impending, my efforts shifted from aconitine-type C19-diterpenoid alkaloids to hetisine- type C20-diterpenoid alkaloids, which will be the focus of the following chapter.

2.7 Experimental Procedures and Characterization Data

All reagents were obtained from commercial chemical suppliers and used without further purification unless otherwise noted. Unless stated otherwise, all reactions were performed in oven-dried glassware sealed with rubber septa under a nitrogen atmosphere and were stirred with Teflon-coated magnetic stir bars. Dry tetrahydrofuran (THF), benzene, toluene, acetonitrile (CH3CN), methanol (MeOH), and triethylamine (Et3N) were degassed with argon for 45 min and passed through activated alumina columns. Dichloromethane (CH2Cl2) was distilled over calcium hydride before use. Reactions were monitored by thin layer chromatography (TLC) on Silicycle SiliaplateTM glass backed TLC plates (250 μm thickness, 60 Å porosity, F-254 indicator) and visualized by UV irradiation and potassium permanganate (KMnO4) or p- anisaldehyde stain. Volatile solvents were removed under reduced pressure with a rotary evaporator. Flash column chromatography was performed either manually using Silicycle 60 Å, 230x400 mesh silica gel (40-63 μm) or automated on a Yamazen Smart Flash W-Prep 2XY system with Yamazen Universal silica gel purification columns, loaded using a Yamazen silica gel inject column. 1H NMR and 13C NMR spectra were taken with Bruker spectrometers 1 13 operating at 300, 400, 500, or 600 MHz for H (75, 100, 125, and 150, MHz for C) in CDCl3. Chemical shifts are reported in parts per million (δ) relative to the residual solvent signal (1H NMR: δ = 7.26; 13C NMR: δ = 77.16). NMR data are reported as follows: chemical shift (multiplicity, coupling constants where applicable, number of hydrogens). Splitting is reported with the following symbols: s = singlet, bs = broad singlet, d = doublet, t = triplet, q = quartet, dd = doublet of doublets, ddd = doublet of doublet of doublets, dt = doublet of triplets, m = multiplet. IR spectra were taken on a Nicolet 380 spectrometer as thin films on NaCl plates or on a Bruker ALPHA FTIR spectrometer and are reported in frequency of absorption (cm-1). Only selected resonances are reported. High-resolution mass spectra (HRMS) were obtained by the mass spectral facility at the University of California, Berkeley using a Finnigan/Thermo LTQ/FT instrument for ESI and a Waters Autospec Premiere Instrument for EI. X-ray crystallographic analysis was performed by the X-ray crystallography facility at the University of California, Berkeley on a MicroStar-H X8 APEX-II diffractometer with Cu-Kα radiation (λ = 1.54178 Å) and structures were visualized using CYLview.

Enyne 2.16. 2-Butyne-1,4-diol (2.15, 141 g, 1.64 mmol) was suspended in H2O (270 mL) in a 2 L round bottom flask and stirred until most of the solids had dissolved. The flask was then cooled to 0 °C and a solution of NaOH (148 g in 250 mL H2O) was added open to air followed by the addition of Me2SO4 (346 mL, 2.2 equiv) over 30 minutes via addition funnel. A reflux condenser was attached and the biphasic reaction mixture was heated to 90-100 °C for 2.5 h using a heating mantle. The reaction was cooled to rt and the organic and aqueous layers were separated. The aqueous layer was extracted with Et2O (2 x 200 mL), and all the organic layers were combined, washed with brine (150 mL), dried over Na2SO4, filtered, and concentrated on a rotary evaporator in a 0 °C bath to provide 2.52 as a volatile light yellow liquid, which was used in the next reaction without further purification. NH3(g) was condensed into a flame-dried 2 L two-neck round bottom flask that was precooled to -78 °C and equipped with a magnetic stir bar and cold finger condenser cooled to -78 °C. A balloon was attached to the neck of the cold finger and the condensation process was allowed to proceed until approximately 1 L of NH3(l) had been collected, at which point the balloon was replaced with a N2 inlet line. Na(s) (40.8 g, 1.75 mol, 2.4 equiv) was rinsed with hexanes and cut into approximately twenty 1 cm3 cubes. One piece of Na(s) was added, followed by Fe(NO3)3 • 9H2O (924 mg, 2.29 mmol, 0.003 equiv). The remainder of the Na(s) was added in 20 s intervals. After the last piece of Na(s) was added, the N2 inlet was replaced with an oil bubbler to monitor H2 gas generation. The reaction mixture was stirred at -78 °C for 2 h, at which time H2 gas generation had ceased. The oil bubbler was removed and the N2 inlet was reattached, after which crude butyne 2.52 (83.3 g, 730 mmol) was added at a rate of 1 mL/min via syringe pump. After addition was complete, the reaction mixture was stirred for an additional 1 h at -78 °C. At that time, NH3 was carefully evaporated over 2 h by removing the cold bath and letting the reaction mixture stir at rt, ensuring adequate N2 flow through the reaction vessel. After most of the NH3 had evaporated, Et2O (250 mL) was slowly added, after which the reaction mixture was cooled to 0 °C and quenched by the dropwise addition of H2O (250 mL0. The resulting dark brown suspension was filtered through Celite with Et2O (200 mL) and extracted with Et2O (2 x 100 mL). The combined organic extracts were washed with brine (100 mL), dried over Na2SO4, and filtered. The volatile product could either be concentrated by distillation of the Et2O at 40-50 °C or on a rotary evaporator in a 0 °C bath to 1 give enyne 2.16 (90.1 g, 2:3 2.16/Et2O by H NMR analysis, ~440 mmol, 60% over 2 steps). This material was used directly in the next step without further purification. 1H NMR (400 MHz, CDCl3) δ 6.95 (d, J = 12.9 Hz, 1H), 4.82 (dd, J = 12.9, 2.4 Hz, 1H), 3.60 (s, 3H), 2.72 (dd, J = 2.4, 0.5 Hz, 1H), in agreement with previously reported spectral data.18

Diene 2.6. Enyne 2.16 (~440 mmol) was diluted with THF (500 mL) under N2 in a flame-dried 2 L round bottom flask and cooled to -78 °C. To this solution was added nBuLi (228 mL, 570 mmol, 2.5 M in hexanes, 1.3 equiv) over 30 min via addition funnel. The solution was moved to a water bath at rt and allowed to stir at rt for 1 h, then cooled to 0 °C. Paraformaldehyde (20.3 g, 676 mmol, 1.5 equiv) was added in a single portion and the reaction mixture was allowed to gradually warm to rt. After 17 h, the resulting mixture was cooled to 0 °C and LiAlH4 was added in 12 portions over 10 min and the reaction mixture was allowed to warm to rt over 90 min. The reaction mixture was then cooled to 0 °C and quenched sequentially with 10 mL EtOAc, 24.3 mL H2O, 24.3 mL 15% NaOH(aq), and 3 x 24.3 mL H2O dropwise. The crude reaction mixture was filtered through Celite and concentrated to provide diene 2.17 as a dark yellow liquid, which was advanced without further purification. To a solution of 2.17 in CH2Cl2 (600 mL) under N2 in a 2 L round bottom flask was added imidazole (52.5 g, 771 mmol, 2.0 equiv) in 3-5 g portions. TBSCl (64.3 g, 427 mmol, 1.2 equiv) was then added in 5-10 g portions and the reaction mixture was allowed to stir at rt for 9 h, during which time a light orange precipitate formed. The reaction mixture was quenched by the addition of sat. NaHCO3 (300 mL) and the organic and aqueous layers were separated. The organic layer was washed with brine (100 mL), dried over Na2SO4, filtered, and concentrated. Column chromatography (0% then 2% then 4% EtOAc in hexanes) afforded diene 2.6 as a pale yellow liquid (54.0 g, 54% over 1 2 steps). H NMR (400 MHz, CDCl3) δ 6.58 (d, J = 12.6 Hz, 1H), 6.20 – 5.94 (m, 1H), 5.69 – 5.39 (m, 2H), 4.18 (dd, J = 5.6, 1.5 Hz, 2H), 3.58 (s, 3H), 0.91 (s, 9H), 0.07 (s, 6H), in agreement with previously reported spectral data.18

(Carbomethoxy)maleic anhydride (CMA, 2.21). To a solution of NaOMe (2.7 g, 50 mmol, 1.0 equiv) in MeOH (50 mL) at 0 °C was added dimethyl malonate (2.18, 5.7 mL, 50 mmol, 1.0 equiv) and the resulting solution was stirred at 0 °C for 30 min. At that time methyl bromoacetate (2.19, 4.7 mL, 50 mmol, 1.0 equiv) was added and the reaction mixture was allowed to stir at rt for 1 h before being heated to reflux for 3 h. At that time, the reaction mixture was concentrated and the residue was suspended in methyl tert-butyl ether (20 mL), which was washed with H2O (2 x 20 mL) and brine (20 mL), dried over MgSO4, filtered, and distilled via Kugelrohr at 135 °C and 0.3 torr. The crude product was then dissolved in CH2Cl2 (20 mL) and cooled to 0 °C. A solution of bromine (1.7 mL, 33 mmol, 1.0 equiv) in CH2Cl2 (10 mL) was added dropwise and the resulting solution heated to reflux for 30 min. At that time, the reaction mixture was cooled to rt and washed with sat. Na2CO3 (40 mL), H2O (40 mL), and brine (40 mL), dried over MgSO4, filtered, and concentrated. This crude product was then added to pyridine (32 mL) and heated to 100 °C for 1 h. After cooling to rt, the reaction mixture was added to H2O (30 mL) and extracted with EtOAc (3 x 50 mL). The combined organic layers were washed with 0.1 mL HCl (50 mL), NaHCO3 (50 mL) and brine (50 mL), dried over MgSO4, filtered, and concentrated. Column chromatography (10% EtOAc in hexanes) afforded triester 2.20. Triester 2.20 (585 mg, 2.9 mmol) and phosphorous pentoxide (820 mg, 5.8 mmol,

2.0 equiv) were mixed in a dry 25 mL round bottom flask and dried under vacuum for 30 min. The reagents were then placed under N2 and heated to 160 °C for 5 h, at which time the residue was distilled via Kugelrohr to provide CMA (2.21) as a yellow oil (216 mg, 13% over 4 steps). 1 H NMR (600 MHz, CDCl3) δ 7.45 (s, 1H), 3.98 (s, 3H), in agreement with previously reported spectral data.6

Benzyl ether 2.23. To a solution of propargyl alcohol (2.22, 1.48 mL, 25 mmol) in THF (25 mL) at 0 oC was added, sequentially, sodium hydride (1.2 g, 60% in mineral oil, 30 mmol), tetrabutylammonium iodide (920 mg, 2.5 mmol), and benzyl bromide (3.56 mL, 30 mmol). The o solution was warmed to 23 C and stirred for 18 hours. At this time, sat. NH4Cl (20 mL) was added and the mixture was extracted with diethyl ether (3 x 20 mL). The combined organic layers were washed with H2O (25 mL) and brine (25 mL), dried over MgSO4, filtered, and concentrated to afford 3.60 g of benzyl ether 2.23 (24.6 mmol, 98% yield). 1H NMR (400 MHz, CDCl3) δ 7.37-7.31 (m, 5H), 4.62 (s, 2H), 4.18 (d, J = 2.4 Hz, 2H), 2.47 (t, J = 2.3 Hz, 1H), in agreement with previously reported spectral data.7

(Benzyloxymethylene)maleic anhydride (BMA, 2.7). To a Parr bomb reaction vessel was added benzyl ether 2.23 (3.00 g, 20.5 mmol, 1.0 equiv), MeOH (100 mL), PdI2 (40 mg, 0.10 mmol, 0.005 equiv), and KI (100 mg, 0.62 mmol, 0.03 equiv). The Parr bomb was sealed and pressurized with CO and air (3:1 CO/air, 560 psi total) before being heated at 65 °C and stirred for 20 h. At this time, the reaction vessel was cooled and the pressure released. The reaction mixture was diluted with CH2Cl2 (150 mL), filtered through Celite with a layer of charcoal on top, filtered through a plug of silica, and concentrated. To a solution of crude diester 2.24 in EtOH (18 mL) was added 2 M NaOH (31 mL) and the reaction mixture was heated at 75 °C for 3 h. At that time, the reaction mixture was cooled to rt and acidified with 1 M HCl (63 mL). The reaction mixture was extracted with EtOAc (3 x 100 mL) and the combined organic phases were dried over MgSO4, filtered, and concentrated. The crude diacid was dissolved in acetic anhydride (100 mL) and the reaction mixture was heated at 75 °C for 1 h at which time the reaction mixture was cooled to rt and concentrated. Column chromatography (10% EtOAc in hexanes) provided 1 BMA (2.7) as a white solid (2.5 g, 56% yield over 3 steps). H NMR (400 MHz, CDCl3) δ 7.41- 7.33 (m, 5H), 6.88 (t, J = 2.2 Hz, 1H), 4.66 (s, 2H), 4.44 (d, J = 2.3 Hz, 2H), in agreement with previously reported spectral data.7

CMA Diels–Alder Adduct 2.25. To a mixture of CMA (2.21, 35 mg, 0.22 mmol) in CDCl3 (0.5 mL) was added diene 2.6 (51 mg, 0.22 mmol). The mixture was stirred for 15 minutes at rt, after which time the solvent was evaporated and the residue was chromatographed (10% EtOAc in hexanes) to afford adduct 2.25 (10 mg, 0.026 mmol, 12% yield). Rf = 0.46 (20% EtOAc in 1 hexanes); H NMR (600 MHz, CDCl3) δ 6.09 (ddd, J = 10.0, 3.8, 2.5 Hz, 1H), 5.98 (ddd, J = 10.0, 3.7, 1.5 Hz, 1H), 4.50 (m, 1H), 4.24 (dd, J = 9.8, 7.7 Hz, 1H), 3.88-3.84 (m, 2H), 3.87 (s, 3H), 3.44 (s, 3H), 2.66 (m, 1H), 0.89 (s, 9H), 0.084 (s, 3H), 0.079 (s, 3H); 13C NMR (150 MHz, CDCl3) δ 168.4, 167.4, 166.1, 131.7, 127.4, 74.2, 62.9, 61.8, 58.5, 54.1, 44.6, 36.8, 26.0, 18.4, - 5.25, -5.31; IR (thin film) 2956, 2930, 2857, 1795, 1788, 1744 cm-1; HRMS (ESI) calcd for + + [C18H28O7SiNa] (M+Na) : m/z 407.1497, found 407.1505.

BMA Diels–Alder Adduct 2.5. To a solution of diene 2.6 (210 mg, 0.92 mmol) in benzene (0.5 ml) was added BMA (2.7, 100 mg, 0.46 mmol). The solution was heated to 40 oC and stirred for 12 hours. The reaction mixture was cooled to rt and chromatographed (15% EtOAc in hexanes with 1% formic acid) to afford adduct 2.5 (131 mg, 0.29 mmol, 64% yield). Rf = 0.48 (20% o 1 EtOAc in hexanes); mp 39-45 C; H NMR (600 MHz, CDCl3) δ 7.44-7.20 (m, 5H), 6.03 (d, J = 9.9 Hz, 1H), 5.95 (d, J = 9.9 Hz, 1H), 4.62 (d, J = 12.1 Hz, 1H), 4.52 (d, J = 12.0 Hz, 1H), 4.21 (dd, J = 9.3, 8.0 Hz, 1H), 4.00 (d, J = 9.2 Hz, 1H), 3.92 (dd, J = 9.6, 8.3 Hz, 1H), 3.66 (m, 2H), 3.52 (d, J = 9.3 Hz, 1H), 3.39 (s, 3H), 2.55 (m, 1H), 0.91 (s, 9H), 0.10 (s, 6H); 13C NMR (150 MHz, CDCl3) δ 170.8, 170.2, 137.2, 131.5, 128.7, 128.1, 127.8, 127.5, 74.7, 73.8, 69.0, 62.9, 58.5, 57.0, 42.1, 36.9, 26.0, 18.4, -5.26, -5.31; IR (thin film) 2954, 2929, 2857, 1856, 1785 cm-1; + + HRMS (ESI) calcd for [C24H34O6SiNa] (M+Na) : m/z 469.2017, found 469.2019.

Amide 2.26. To a solution of adduct 2.5 (50 mg, 0.11 mmol) in DCM (2 mL) was added cyclohexylamine (15 μL, 0.13 mmol) as a solution in DCM. The mixture was stirred at 23 oC for 30 minutes at which time the organic solvents were removed with a rotary evaporator. The crude

24 product was dissolved in toluene (2 mL), followed by the addition of methanol (0.8 mL) and trimethylsilyldiazomethane (0.1 mL, 2.0M in diethyl ether, 0.2 mmol). The mixture was stirred for 15 minutes at 23 oC, at which time the organic solvents were removed with a rotary evaporator. The residue was chromatographed (10% then 50% EtOAc in hexanes) to afford 1 amide 2.26 (20 mg, 0.033 mmol, 30% yield). Rf = 0.76 (50% ethyl acetate in hexanes); H NMR (400 MHz, CDCl3) δ 7.41-7.18 (m, 5H), 6.07 (d, J = 10.4 Hz, 1H), 5.94 (dt, J = 10.4, 2.7 Hz, 1H), 4.46 (s, 2H), 3.96 (dd, J = 10.0, 4.8 Hz, 1 H), 3.75-3.63 (m, 2H), 3.69 (s, 3H), 3.55 (d, J = 3.5 Hz, 1H), 3.42 (s, 3H), 3.39-3.31 (m, 3H), 2.38 (m, 1H), 1.77 (m, 2H), 1.59 (m, 3H), 1.33 13 (m, 2H), 1.19 (m, 1H), 1.05 (m, 2H), 0.89 (s, 9H), 0.04 (s, 6H); C NMR (100 MHz, CDCl3) δ 172.7, 169.8, 137.8, 131.1, 128.5, 127.9, 127.7, 122.3, 75.3, 73.4, 72.7, 64.0, 58.1, 53.8, 52.0, 47.7, 43.3, 37.3, 33.0, 32.4, 26.1, 25.9, 24.5, 18.4, -5.1, -5.2; IR (thin film) 3313, 2929, 2855, -1 + + 1745, 1658, 1641 cm ; HRMS (ESI) calcd for [C31H50O6NSi] (M+H) : m/z 560.3402, found 560.3407.

Ester 2.27. A solution of adduct 2.5 (50 mg, 0.11 mmol) in MeOH (3 mL) was heated to 110 oC for 1 hour in a microwave reactor, after which point the solvent was removed with a rotary evaporator and the residue dissolved in 2 mL of CH2Cl2. To this solution was added CDI (21 mg, 0.13 mmol) and the mixture was stirred for 15 minutes at which time cyclohexylamine (0.02 mL, 0.14 mmol) was added. The solution was stirred at 23 oC for 12 hours at which time 2 mL of a saturated NH4Cl solution was added. The mixture was extracted with Et2O (3 x 2 mL) and the organic layer was dried over MgSO4, filtered, and concentrated. The concentrate was chromatographed (20% EtOAc in hexanes) to afford ester 2.27 (15 mg, 0.027 mmol, 25% yield). 1 Rf = 0.57 (50% ethyl acetate in hexanes); H NMR (600 MHz, CDCl3) δ 10.99 (bs, 1H), 7.35- 7.24 (m, 5H), 6.16 (d, J = 10.4 Hz, 1H), 6.02 (d, J = 10.3 Hz, 1H), 4.46 (dd, J = 22.7, 12.4 Hz, 2H), 3.96 (dd, J = 9.5, 4.89 Hz, 1H), 3.76 (s, 3H), 3.71 (d, J = 7.4 Hz, 2H), 3.62 (d, J = 6.7 Hz, 1H), 3.50-5.45 (m, 1H), 3.48 (s, 3H), 3.38-3.33 (m, 2H), 2.43 (s, 1H), 1.94 (m, 1H), 1.70 (m, 1H), 1.57 (m, 4H), 1.35 (m, 2H), 1.13 (m, 2H), 0.89 (s, 9H), 0.062 (s, 3H), 0.055 (s, 3H); 13C NMR (150 MHz, CDCl3) δ 172.6, 171.2, 137.4, 133.1, 128.6, 128.1, 127.8, 121.2, 74.6, 73.5, 71.4, 63.8, 57.8, 53.7, 52.7, 42.5, 36.9, 34.1, 26.05, 26.03, 25.8, 25.1, 18.4, -5.2, -5.3; IR (thin -1 + + film) 2927, 2855, 1743 cm ; HRMS (ESI) calcd for [C31H50O6NSi] (M+H) : m/z 560.3402, found 560.3418.

Lactone 2.28. To a solution of adduct 2.5 (50 mg, 0.11 mmol) in MeOH (2 mL) was added 12 drops of 1M HCl. The solution was stirred at 23 oC for 20 minutes, at which time the organic solvents were evaporated, and the crude residue was dissolved in toluene (1 mL). MeOH (0.4 mL) was added, followed by trimethylsilyldiazomethane (0.2 mL, 2.0M in diethyl ether, 0.4 mmol). The mixture was stirred at 23 oC for 15 minutes, concentrated with a rotary evaporator, and chromatographed (20% EtOAc in hexanes) to afford lactone 2.28 (8 mg, 0.023 mmol, 21% 1 yield). Rf = 0.54 (50% EtOAc in hexanes); H NMR (600 MHz, CDCl3) δ 7.37-7.29 (m, 5H), 5.96 (dt, J = 10.1, 2.8 Hz, 1H), 5.67 (dt, J = 10.1, 2.5 Hz, 1H), 4.62 (d, J = 11.9 Hz, 1H), 4.53 (d, J = 11.9 Hz, 1H), 4.42 (t, J = 8.6 Hz, 1H), 4.13 (dd, J = 8.2, 6.9 Hz, 1H), 4.09 (m, 1H), 3.92 (d, J = 9.1 Hz, 1H), 3.88 (d, J = 9.1 Hz, 1H), 3.70 (s, 3H), 3.42-3.40 (m, 1H), 3.41 (s, 3H), 3.13 (m, 13 1H); C NMR (150 MHz, CDCl3) δ 176.2, 171.3, 138.1, 128.6, 127.98, 127.95, 127.9, 126.5, 75.1, 73.5, 70.7, 69.1, 58.6, 52.29, 52.27, 38.3, 34.5; IR (thin film) 2927, 2359, 2341, 1763, -1 + + 1731 cm ; HRMS (ESI) calcd for [C19H23O6] (M+H) : m/z 347.1489, found 347.1494.

Lactone 2.29. To a suspension of sodium borohydride (8 mg, 0.22 mmol) in THF (1 mL) at 0 oC was added a solution of adduct 2.5 (50 mg, 0.11 mmol) in THF (1 mL). The solution was o warmed to 23 C and stirred for 2 hours at which time 3 mL of a saturated NH4Cl solution was added. The mixture was extracted with diethyl ether (3 x 3 mL), dried over MgSO4, and filtered, and the organic solvents were evaporated. The residue was chromatographed (10% EtOAc in hexanes) to afford lactone 2.29 (24 mg, 0.056 mmol, 51% yield). Rf = 0.58 (20% ethyl acetate in 1 hexanes); H NMR (600 MHz, CDCl3) δ 7.40-7.23 (m, 5H), 6.00 (d, J = 9.7 Hz, 1H), 5.88 (d, J = 9.8 Hz, 1H), 4.59 (d, J = 12.1 Hz, 1H), 4.54 (d, J = 12.1 Hz, 1H), 4.26 (d, J = 9.7 Hz, 1H), 4.10 (m, 1H), 3.91 (m, 1H), 3.83 (s, 1H), 3.82 (d, J = 9.9 Hz, 1H), 3.63 (d, J = 8.8 Hz, 1H), 3.47 (d, J = 8.8 Hz, 1H), 3.37 (s, 3H), 3.08 (d, J = 6.6 Hz, 1H), 2.45 (m, 1H), 0.90 (s, 9H), 0.08 (s, 6H); 13 C NMR (150 MHz, CDCl3) δ 177.5, 138.0, 131.1, 130.4, 128.6, 128.0, 127.7, 77.0, 73.6, 72.5, 70.9, 62.9, 58.1, 50.1, 44.0, 38.6, 26.1, 18.5, -5.15, -5.21; IR (thin film) 2954, 2928, 2856, 1770 -1 + + cm ; HRMS (ESI) calcd for [C24H36O5SiNa] (M+Na) : m/z 455.2224, found 455.2227.

Arylacetic Ester 2.31. To a flask containing MeOH (800 mL) at 0 °C was added dropwise acetyl chloride (36.0 mL, 506 mmol, 3.5 equiv) and the reaction mixture was stirred at 0 °C for 10 min. 3-Methoxyphenylacetic acid (2.53, 24.0 g, 144 mmol) was added and the reaction mixture was stirred at rt for 16 h, at which point the reaction mixture was concentrated. Column chromatography (4:1 hexanes/EtOAc) provided arylacetic ester 2.31 as a colorless oil (25.8 g, 1 143 mmol, 99% yield). Rf: 0.55 (4:1 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 7.29 (d, J = 7.2 Hz, 1H), 6.92 – 6.84 (m, 3H), 3.84 (s, 3H), 3.73 (s, 3H), 3.64 (s, 2H), in agreement with previously reported spectral data.8b 26

Benzyl Ether 2.38. To a solution of but-3-yn-1-ol (2.37, 15.0 mL, 198 mmol, 1.2 equiv) in THF (165 mL) at 0 °C was added, sequentially, sodium hydride (7.93 g, 60% in mineral oil, 198 mmol, 1.2 equiv), tetrabutylammonium iodide (6.09 g, 16.5 mmol, 0.10 equiv), and benzyl bromide (19.6 mL, 165 mmol, 1 equiv). The solution was warmed to rt and stirred for 18 h, at which time the reaction was quenched by the addition of sat. NH4Cl(aq) and extracted with Et2O (3 x 100 mL). The combined organic phases were washed with H2O (100 mL) and brine (100 mL), dried over MgSO4, filtered, and concentrated. Column chromatography (19:1 hexanes/EtOAc) provided benzyl ether 2.38 as a light yellow oil (26.4 g, 165 mmol, quant.). Rf: 1 0.80 (4:1 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 7.36 – 7.28 (m, 5H), 4.57 (s, 2H), 3.61 (t, J = 6.9 Hz, 2H), 2.51 (td, J = 6.9, 2.7 Hz, 2H), 2.00 (t, J = 2.7 Hz, 1H); in agreement with previously reported spectral data.19

Diester 2.39. To a Parr bomb reaction vessel was added benzyl ether 2.38 (6.00 g, 37.5 mmol, 1 equiv), MeOH (160 mL), PdI2 (134 mg, 0.37 mmol, 0.01 equiv), and KI (620 mg, 3.72 mmol, 0.10 equiv). The Parr bomb was sealed and pressurized with CO and air (2.5:1 CO/air, 560 psi total) before being heated at 60 °C and stirred for 60 h. At this time, the reaction vessel was cooled and the pressure released. The reaction mixture was diluted with CH2Cl2 (150 mL), filtered through Celite with a layer of charcoal on top, and concentrated. Column chromatography (4:1 hexanes/EtOAc) provided diester 2.39 as a light yellow oil (6.74 g, 24.2 1 mmol, 65% yield). Rf: 0.29 (4:1 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 7.37 – 7.28 (m, 5H), 5.94 (t, J = 1.4 Hz, 1H), 4.51 (s, 2H), 3.78 (s, 3H), 3.73 (s, 3H), 3.62 (t, J = 6.3 13 Hz, 2H), 2.66 (td, J = 6.3, 1.4 Hz, 2H). C NMR (100 MHz, CDCl3) δ 169.0, 166.5, 147.0, -1 138.0, 128.5, 127.8, 121.5, 73.2, 67.3, 52.5, 52.0, 34.8. IR (thin film) ṽmax cm 3441, 2096, + + 1647. HRMS (ESI) calcd for [C15H18O5Na] ([M+Na] ): m/z 301.1046, found 301.1043.

Dienophile 2.40. To a solution of diester 2.39 (7.49 g, 26.9 mmol) in EtOH (24 mL) was added 2 M NaOH (41.5 mL, 83 mmol, 3 equiv) and the reaction mixture was heated at 75 °C for 3 h. At that time, the reaction mixture was cooled to rt and acidified with 1 M HCl (100 mL). The reaction mixture was extracted with EtOAc (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried over MgSO4, filtered, and concentrated. The crude diacid was dissolved in acetic anhydride (119 mL) and the reaction mixture was heated at 75 °C for 1 h at which time the reaction mixture was cooled to rt and concentrated. Column chromatography (4:1 hexanes/EtOAc) provided dienophile 2.40 as a light yellow solid (4.05 g, 17.4 mmol, 65% yield). 1 mp: 64 – 65 °C. Rf: 0.39 (4:1 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 7.39 – 7.28 (m, 5H), 6.71 (t, J = 1.7 Hz, 1H), 4.53 (s, 2H), 3.75 (t, J = 5.8 Hz, 2H), 2.80 (td, J = 5.8, 1.7 13 Hz, 2H). C NMR (100 MHz, CDCl3) δ 166.0, 164.1, 150.6, 137.4, 130.4, 128.7, 128.2, 128.0, -1 73.4, 66.1, 26.6. IR (thin film) ṽmax cm 3109, 2881, 1841, 1773, 1644, 1265, 1238. HRMS + + (ESI) calcd for [C13H12O4Na] ([M+Na] ): m/z 255.0628, found 255.0627.

Diels–Alder Adduct 2.41. A solution of dienophile 2.40 (14.3 g, 61.7 mmol) and diene 2.6 (21.1 g, 92.6 mmol, 1.5 equiv) in toluene (110 mL) was heated under reflux for 24 h, at which time the reaction mixture was cooled to rt and concentrated. Column chromatography (7:1 hexanes/EtOAc) provided Diels–Alder adduct 2.41 as a light yellow oil (20.4 g, 44.3 mmol, 72% 1 yield). Rf: 0.46 (4:1 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 7.36 – 7.28 (m, 3H), 7.27 – 7.24 (m, 2H), 6.08 – 5.99 (m, 2H), 4.49 (d, J = 11.9 Hz, 1H), 4.38 (d, J = 11.9 Hz, 1H), 4.15 (dd, J = 9.7, 7.0 Hz, 1H), 3.87 (dd, J = 9.7, 8.7 Hz, 1H), 3.63 (d, J = 3.6 Hz, 1H), 3.60 (t, J = 5.7 Hz, 2H), 3.53 (d, J = 7.0 Hz, 1H), 3.38 (s, 3H), 2.58 (d, J = 8.2 Hz, 1H), 2.42 (dt, J = 14.8, 5.6 Hz, 1H), 1.87 (dt, J = 14.8, 5.8 Hz, 1H), 0.89 (s, 9H), 0.07 (s, 6H). 13C NMR (100 MHz, CDCl3) δ 172.6, 170.4, 137.5, 132.2, 128.7, 128.1, 128.0, 126.9, 77.7, 73.5, 66.0, 63.1, -1 58.2, 53.9, 43.4, 37.0, 32.1, 26.0, 18.4, -5.2, -5.3. IR (thin film) ṽmax cm 2953, 2928, 2857, + + 1849, 1782, 1090, 837. HRMS (ESI) calcd for [C25H36O6SiNa] ([M+Na] ): m/z 483.2173, found 483.2164.

Decarboxylated Tricycle 2.43. To a solution of arylacetic ester 2.31 (3.39 g, 18.1 mmol, 1.6 equiv) in THF (70 mL) at -78 °C was added LiHMDS (1.0 M in THF, 17.6 mL, 17.6 mmol, 1.5

28 equiv) and the reaction mixture was allowed to stir at -78 °C for 30 min. A solution of Diels– Alder adduct 2.41 (5.42 g, 11.8 mmol) in THF (48 mL) was added dropwise and the reaction mixture was stirred at -78 °C for 5 h, at which time the reaction mixture was quenched with sat. NH4Cl(aq) (20 mL). The reaction mixture was extracted with EtOAc (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried over MgSO4, filtered, and concentrated. The crude alcohol was then dissolved in MeOH (108 mL) and 1 M HCl (35 mL) was added. The reaction mixture was stirred at rt for 3 h, at which point the reaction mixture was concentrated. Column chromatography (35% EtOAc in hexanes) provided tricyclic acetal 2.42 as a colorless gum (4.46 g, 8.77 mmol, 75% yield, 51:49 dr). To a microwave vial was added the mixture of diastereomers of tricyclic acetal 2.42 (557 mg, 1.10 mmol), DMF (13.5 mL), H2O (1.5 mL), and LiCl (232 mg, 5.48 mmol, 5 equiv). The microwave vial was sealed and heated in the microwave (225 °C, 30 min, very high absorbance, 30 s pre-stirring). This process was carried out in 8 separate batches. Once cooled, all 8 reaction mixtures were combined, diluted with Et2O, washed with brine (100 mL), dried over MgSO4, filtered, and concentrated. Column chromatography (35% EtOAc in hexanes) provided decarboxylated tricycle 2.43 as a light 1 yellow oil (3.42 g, 7.59 mmol, 87% yield). Rf: 0.60 (1:1 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 7.36 – 7.33 (m, 2H), 7.30 – 7.27 (m, 3H), 7.16 (t, J = 7.9 Hz, 1H), 6.85 (s, 1H), 6.80 (d, J = 6.4 Hz, 2H), 6.19 (dd, J = 9.7, 5.3 Hz, 1H), 6.00 (dd, J = 9.7, 6.6 Hz, 1H), 4.47 (d, J = 9.6 Hz, 1H), 4.40 (d, J = 9.6 Hz, 1H), 4.09 – 4.03 (m, 2H), 3.81 (d, J = 5.3 Hz, 1H), 3.77 (s, 3H), 3.48 – 3.39 (m, 2H), 3.25 (s, 3H), 3.22 (d, J = 11.2 Hz, 1H), 3.02 (d, J = 10.8 Hz, 1H), 2.93 (d, J = 7.6 Hz, 1H), 2.59 – 2.53 (m, 1H), 1.74 (t, J = 6.2 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ 176.7, 159.5, 138.0, 136.6, 132.0, 129.6, 129.3, 128.5, 127.7, 127.6, 123.1, 116.3, -1 116.2, 112.8, 76.4, 73.0, 66.2, 57.3, 55.3, 53.1, 48.5, 44.4, 38.3, 36.2. IR (thin film) ṽmax cm + + 3454, 2924, 1776, 1766, 1600, 1264, 1087. HRMS (ESI) calcd for [C27H31O6] ([M+H] ): m/z 451.2115, found 451.2121.

Alcohol 2.44. To a solution of decarboxylated tricycle 2.43 (12.2 g, 30.1 mmol) in EtOAc (2.74 L) was added palladium on carbon (5 wt% wet Degussa type E101 NO/W, 6.42 g, 3.01 mmol, 0.10 equiv). A balloon of H2 was appended and bubbled through the stirred reaction mixture at rt for 1 h. The reaction mixture was then filtered through Celite and concentrated to provide alcohol 2.44 as a white solid (9.12 g, 25.2 mmol, 84% yield). mp: 132 – 134 °C. Rf: 0.45 (1:4 1 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 7.21 (t, J = 8.1 Hz, 1H), 6.89 – 6.87 (m, 2H), 6.81 – 6.79 (m, 1H), 3.92 (t, J = 8.4 Hz, 1H), 3.82 (dd, J = 8.0, 5.6 Hz, 1H), 3.79 – 3.75 (m, 4H), 3.73 – 3.68 (m, 1H), 3.38 – 3.34 (m, 2H), 3.33 (s, 3H), 3.10 (d, J = 14.1 Hz, 1H), 2.54 (d, J = 10.2 Hz, 1H), 2.30 (t, J = 3.6 Hz, 1H), 2.16 – 2.10 (m, 1H), 1.82 – 1.78 (m, 1H), 1.75 – 13 1.71 (m, 1H), 1.64 – 1.55 (m, 3H), 1.52 – 1.48 (m, 1H). C NMR (100 MHz, CDCl3) δ 176.8, 159.6, 136.7, 129.4, 123.0, 117.1, 116.3, 112.7, 80.2, 72.0, 59.1, 57.4, 55.4, 51.0, 48.1, 43.6,

-1 40.0, 34.7, 20.7, 17.9. IR (thin film) ṽmax cm 3494, 2937, 1764, 1602, 1584, 1491, 1455, 1263, + + 1091. HRMS (ESI) calcd for [C20H26O6Na] ([M+Na] ): m/z 385.1622, found 385.1625.

Vinyl Lactone 2.45. To a solution of alcohol 2.44 (1.24 g, 3.42 mmol) and o- nitrophenylselenocyanide (1.55 g, 6.84 mmol, 2 equiv) in THF (56 mL) under N2 was added PBu3 (1.71 mL, 6.84 mmol, 2 equiv) and the reaction mixture was stirred at rt for 16 h. EtOH (30 mL) was then added and the reaction mixture was concentrated. The residue was then dissolved in THF (60 mL) and cooled to 0 °C before H2O2 (30% w/w in H2O, 4.0 mL, 35.3 mmol, 10 equiv) was added. The reaction mixture was allowed to warm to rt and stirred for 16 h, at which time the reaction mixture was diluted with H2O (100 mL) and extracted with Et2O (3 x 100 mL). The combined organic phases were washed with brine (100 mL), dried over MgSO4, filtered, and concentrated. Column chromatography (1:1 hexanes/EtOAc) provided vinyl lactone 2.45 as an orange solid (1.12 g, 3.25 mmol, 95% yield). mp: 63 – 64 °C. Rf: 0.52 (1:1 hexanes/EtOAc, 1 KMnO4). H NMR (400 MHz, CDCl3) δ 7.19 (t, J = 7.9 Hz, 1H), 6.83 – 6.77 (m, 3H), 5.79 (dd, J = 17.4, 10.6 Hz, 1H), 5.30 (d, J = 10.0 Hz, 1H), 5.27 (d, J = 17.2 Hz, 1H), 3.94 (t, J = 8.4 Hz, 1H), 3.79 (s, 3H), 3.74 (dd, J = 11.8, 8.8 Hz, 1H), 3.37 – 3.33 (m, 4H), 3.21 (dd, J = 9.3, 2.6 Hz, 1H), 2.92 (d, J = 14.1 Hz, 1H), 2.62 (d, J = 10.4 Hz, 1H), 2.22 – 2.12 (m, 1H), 1.75 – 1.69 (m, 13 1H), 1.64 – 1.51 (m, 4H). C NMR (100 MHz, CDCl3) δ 173.6, 159.6, 138.1, 136.5, 129.3, 123.0, 116.9, 116.5, 116.4, 112.6, 81.6, 71.1, 58.4, 55.9, 55.3, 48.3, 43.2, 34.6, 21.4, 19.5. IR -1 (thin film) ṽmax cm 2937, 2873, 1774, 1601, 1491, 1453, 1263. HRMS (ESI) calcd for + + [C20H25O5] ([M+H] ): m/z 345.1697, found 345.1695.

Ethyl Amide 2.46. To a solution of vinyl lactone 2.45 in THF (1 mL) in a 5 mL microwave vial was added ethylamine (4 mL, 70% in H2O). The microwave vial was then sealed and the reaction mixture was heated to 60 °C for 3 days, at which time the reaction mixture was allowed to cool to rt and extracted with EtOAc (3 x 10 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated. Automated column chromatography (50 → 71% EtOAc in hexanes gradient) provided ethyl amide 2.46 (76 mg, 71% yield). Rf: 0.16 (1:1

1 hexanes/EtOAc, KMnO4). H NMR (500 MHz, CDCl3) δ 7.16 (t, J = 8.4 Hz, 1H), 6.76 – 6.71 (m, 3H), 5.74 (dd, J = 17.7, 11.0 Hz, 1H), 5.28 (s, 1H), 5.14 (d, J = 11.0 Hz, 1H), 4.93 (d, J = 17.7 Hz, 1H), 4.05 (d, J = 10.8 Hz, 1H), 3.88 – 3.84 (m, 1H), 3.77 – 3.72 (m, 4H), 3.65 (d, J = 2.9 Hz, 1H), 3.49 (d, J = 16.0 Hz, 1H), 3.40 – 3.36 (m, 4H), 3.30 (dd, J = 14.0, 7.0 Hz, 1H), 3.13 (d, J = 16.0 Hz, 1H), 2.49 (d, J = 5.6 Hz, 1H), 2.04 – 1.99 (m, 1 H), 1.91 – 1.83 (m, 2H), 1.52 – 13 1.44 (m, 2H), 1.28 (t, J = 7.2 Hz, 3H). C NMR (125 MHz, CDCl3) δ 175.3, 159.8, 137.7, 136.8, 129.7, 122.0, 117.0, 115.7, 112.4, 92.9, 64.9, 57.4, 55.3, 52.5, 42.4, 40.2, 36.7, 35.5, 29.9, 23.0, 19.4, 14.5.

Methylated Lactone 2.48. Ethyl amide 2.46 (76 mg, 0.195 mmol) was transferred to a 5 mL microwave vial with < 0.5 mL CH2Cl2. EtOAc (5 mL) was added followed by IBX (164 mg, 0.585 mmol, 3.0 equiv). The microwave vial was then sealed and the reaction mixture was heated to reflux for 24 h at which time the solution was filtered through Celite with EtOAc and concentrated. Automated column chromatography (33 → 53% EtOAc in hexanes gradient) provided lactone 2.47 (63 mg, 84% yield). To a solution of lactone 2.47 (52 mg, 0.135 mmol) in CH2Cl2 (3 mL) was added iodomethane (0.04 mL, 0.675 mmol, 5.0 equiv) and the solution was cooled to 0 °C. KOtBu (0.16 mL, 1.0 M in THF, 0.162 mmol, 1.2 equiv) was added and the reaction mixture was stirred at 0 °C for 2 h, at which time another portion of KOtBu (0.08 mL, 1.0 M in THF, 0.6 equiv) was added. The reaction mixture was then stirred for an additional 1 h, at which time the reaction was quenched with H2O (5 mL) and extracted with EtOAc (3 x 10 mL). The combined organic layers were washed with brine (10 mL), dried over MgSO4, filtered, and concentrated to afford methylated lactone 2.48 (45 mg, 83% yield). Rf: 0.50 (1:1 1 hexanes/EtOAc, KMnO4). H NMR (500 MHz, CDCl3) δ 7.18 (t, J = 8.0 Hz, 1H), 6.77 (dd, J = 8.3, 2.2 Hz, 1H), 6.65 (d, J = 7.6 Hz, 1H), 6.59 (s, 1H), 5.66 (dd, J = 17.6, 10.9 Hz, 1H), 4.96 (d, J = 10.9 Hz, 1H), 4.58 (d, J = 17.6 Hz, 1H), 3.87 – 3.80 (m, 1H), 3.74 (s, 3H), 3.68 (d, J = 14.9 Hz, 1H), 3.56 (d, J = 3.5 Hz, 1H), 3.42 – 3.35 (m, 1H), 3.15 (s, 3H), 3.02 (d, J = 15.0 Hz, 1H), 2.66 (s, 1H), 2.33 – 2.24 (m, 1H), 1.87 – 1.80 (m, 1H), 1.47 – 1.39 (m, 2H), 1.38 (s, 3H), 1.30 (t, 13 J = 7.2 Hz, 3H). C NMR (125 MHz, CDCl3) δ 179.9, 175.5, 159.8, 136.8, 135.6, 129.8, 122.2, 116.0, 115.7, 112.8, 99.1, 78.4, 55.5, 55.3, 53.3, 46.5, 41.4, 40.3, 36.0, 29.8, 26.0, 17.2, 14.0. IR -1 (thin film) ṽmax cm 2936, 2359, 1777, 1705, 1602, 1491, 1408, 1263, 1102, 998, 922. HRMS + + (ESI) calcd for [C23H29NO5Na] ([M+Na] ): m/z 422.1938, found 422.1932.

2.8 References (1) Wiesner, K.; Tsai, T. Y. R.; Huber, K.; Bolton, S. E. J. Am. Chem. Soc. 1974, 96, 4490-4492. (2) (a) Tikhonov, D. B.; Zhorov, B. S. FEBS Letters 2005, 579, 4207-4212. (b) Chan, T. Y. K. Clinical Toxicology 2009, 47, 279-285. (3) Streit, U.; Bochet, C. G. Beilstein J. Org. Chem. 2011, 7, 525-542.

(4) Atodiresei, I.; Schiffers, I.; Bolm, C. Chem. Rev. 2007, 107, 5683-5712. (5) (a) Hall, H. K., Jr.; Nogues, P.; Rhoades, J. W.; Sentman, R. C.; Detar, M. J. Org. Chem. 1982, 47, 1451-1455. (b) Forrest, A. K.; Schmidt, R. R.; Huttner, G.; Jibril, I. J. Chem. Soc., Perkin Trans. 1 1984, 1981-1987. (6) Hall, H. K., Jr.; Nogues, P.; Rhoades, J. W.; Sentman, R. C.; Detar, M. J. Org. Chem. 1982, 47, 1451-1455. (7) Spiegel, D. A.; Njardarson, J. T.; Wood, J. L. Tetrahedron 2002, 58, 6545-6554. (8) (a) Rafiq, M.; Saleem, M.; Hanif, M.; Abbas, Q.; Lee, K. H.; Seo, S.-Y. Russ. J. Bioorganic Chem. 2015, 41, 170-177. (b) Hutchby, M.; Houlden, C. E.; Haddow, M. F.; Tyler, S. N. G.; Lloyd-Jones, G. C.; Booker-Milburn, K. I. Angew. Chem. Int. Ed. 2012, 51, 548-551. (9) Griffith, W. P.; Ley, S. V.; Whitcombe, G. P.; White, A. D. J. Chem. Soc., Chem. Commun. 1987, 1625-1627. (10) Lebel, H.; Paquet, V. J. Am. Chem. Soc. 2004, 126, 320-328. (11) Lebrun, M.-E.; Marquand, P. L.; Berthelette, C. J. Org. Chem. 2006, 71, 2009-2013. (12) Pine, S. H.; Zahler, R.; Evans, D. A.; Grubbs, R. H. J. Am. Chem. Soc. 1980, 102, 3270- 3272. (13) Lombardo, L. Tetrahedron Lett. 1982, 23, 4293-4296. (14) Krapcho, A. P.; Weimaster, J. F.; Eldridge, J. M.; Jahngen, E. G. E.; Lovey, A. J.; Stephens, W. P. J. Org. Chem. 1978, 43, 138-147. (15) Grieco, P. A.; Gilman, S.; Nishizawa, M. J. Org. Chem. 1976, 41, 1485-1486. (16) Frigerio, M.; Santagostino, M.; Sputore, S.; Palmisano, G. J. Org. Chem. 1995, 60, 7272- 7276. (17) Marth, C. J.; Gallego, G. M.; Lee, J. C.; Lebold, T. P.; Kulyk, S.; Kou, K. G. M.; Qin, J.; Lilien, R.; Sarpong, R. Nature 2015, 528, 493-498. (18) Kou, K. G. M.; Li, B. X.; Lee, J. C.; Gallego, G. M.; Lebold, T. P.; DiPasquale, A.; Sarpong, R. J. Am. Chem. Soc. 2016, 138, 10830-10833. (19) Ghosh, A. K.; Gong, G. Chem. Asian J. 2008, 3, 1811-1823.

Appendix 1

NMR Spectra and Crystallography Data for Compounds Discussed in Chapter 2

X-Ray Crystallography Data for Diels–Alder Adduct 2.5

A colorless plate 0.12 x 0.10 x 0.02 mm in size was mounted on a Cryoloop with Paratone oil. Data were collected in a nitrogen gas stream at 100(2) K using phi and omega scans. Crystal-to- detector distance was 60 mm and exposure time was 10 seconds per frame using a scan width of 1.0°. Data collection was 98.9% complete to 67.00° in . A total of 22451 reflections were collected covering the indices, -6<=h<=8, -26<=k<=26, -18<=l<=18. 4221 reflections were found to be symmetry independent, with an Rint of 0.0422. Indexing and unit cell refinement indicated a primitive, monoclinic lattice. The space group was found to be P2(1)/c (No. 14). The data were integrated using the Bruker SAINT software program and scaled using the SADABS software program. Solution by direct methods (SIR-2011) produced a complete heavy-atom phasing model consistent with the proposed structure. All non-hydrogen atoms were refined anisotropically by full-matrix least-squares (SHELXL-97). All hydrogen atoms were placed using a riding model. Their positions were constrained relative to their parent atom using the appropriate HFIX command in SHELXL-97.

Table 1. Crystal data and structure refinement for sarpong29. X-ray ID sarpong29 Sample/notebook ID JJPI-126 Empirical formula C24 H34 O6 Si Formula weight 446.60 Temperature 100(2) K Wavelength 1.54178 Å Crystal system Monoclinic Space group P2(1)/c Unit cell dimensions a = 6.9614(3) Å = 90°. b = 22.3685(10) Å = 96.790(3)°. c = 15.3393(6) Å  = 90°. Volume 2371.82(17) Å3 Z 4 Density (calculated) 1.251 Mg/m3 Absorption coefficient 1.176 mm-1 F(000) 960 Crystal size 0.12 x 0.10 x 0.02 mm3 Crystal color/habit colorless plate Theta range for data collection 3.51 to 67.75°. Index ranges -6<=h<=8, -26<=k<=26, -18<=l<=18 Reflections collected 22451 Independent reflections 4221 [R(int) = 0.0422] Completeness to theta = 67.00° 98.9 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.9769 and 0.8717 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4221 / 0 / 286 Goodness-of-fit on F2 1.040 Final R indices [I>2sigma(I)] R1 = 0.0504, wR2 = 0.1307 R indices (all data) R1 = 0.0613, wR2 = 0.1408 Largest diff. peak and hole 0.543 and -0.221 e.Å-3

Table 2. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for sarpong29. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. ______x y z U(eq) ______C(1) 4537(3) -377(1) 7888(1) 27(1) C(2) 2994(3) -862(1) 7570(1) 28(1) C(3) 2971(3) -989(1) 6602(1) 29(1) C(4) 2883(3) -534(1) 6052(1) 31(1) C(5) 2983(3) 89(1) 6431(1) 29(1) C(6) 4695(3) 97(1) 7173(1) 28(1) C(7) 6607(3) -41(1) 6837(1) 32(1) C(8) 6555(3) -655(1) 8028(1) 30(1) C(9) 4112(3) -104(1) 8761(1) 28(1) C(10) 1859(3) 523(1) 9336(1) 29(1) C(11) -49(3) 843(1) 9110(1) 27(1) C(12) -717(3) 994(1) 8246(1) 30(1) C(13) -2447(3) 1305(1) 8055(1) 33(1) C(14) -3520(3) 1463(1) 8724(2) 34(1) C(15) -2855(3) 1316(1) 9587(1) 31(1) C(16) -1138(3) 1007(1) 9775(1) 29(1) C(17) 1715(4) -1767(1) 8051(2) 38(1) C(18) 3116(4) 575(1) 5745(1) 35(1) C(19) 2939(5) 2264(1) 6871(2) 54(1) C(20) -437(4) 1585(2) 5858(2) 52(1) C(21) 2771(3) 2083(1) 4863(1) 33(1) C(22) 2215(4) 1653(1) 4100(1) 40(1) C(23) 1735(5) 2680(1) 4688(2) 62(1) C(24) 4957(4) 2182(1) 4922(2) 56(1) O(1) 7612(2) -470(1) 7364(1) 34(1) O(2) 2337(2) 205(1) 8590(1) 31(1) O(3) 3343(2) -1372(1) 8111(1) 33(1) O(4) 7318(2) 166(1) 6237(1) 42(1) O(5) 7265(2) -965(1) 8602(1) 37(1) O(6) 3448(2) 1138(1) 6173(1) 38(1) Si(1) 2188(1) 1755(1) 5935(1) 32(1) 57

Table 3. Bond lengths [Å] and angles [°] for sarpong29. ______C(1)-C(8) 1.528(3) C(14)-H(14) 0.9500 C(1)-C(9) 1.531(3) C(15)-C(16) 1.382(3) C(1)-C(6) 1.539(3) C(15)-H(15) 0.9500 C(1)-C(2) 1.565(3) C(16)-H(16) 0.9500 C(2)-O(3) 1.415(2) C(17)-O(3) 1.430(3) C(2)-C(3) 1.510(3) C(17)-H(17A) 0.9800 C(2)-H(2) 1.0000 C(17)-H(17B) 0.9800 C(3)-C(4) 1.319(3) C(17)-H(17C) 0.9800 C(3)-H(3) 0.9500 C(18)-O(6) 1.426(3) C(4)-C(5) 1.507(3) C(18)-H(18A) 0.9900 C(4)-H(4) 0.9500 C(18)-H(18B) 0.9900 C(5)-C(18) 1.525(3) C(19)-Si(1) 1.858(3) C(5)-C(6) 1.547(3) C(19)-H(19A) 0.9800 C(5)-H(5) 1.0000 C(19)-H(19B) 0.9800 C(6)-C(7) 1.514(3) C(19)-H(19C) 0.9800 C(6)-H(6) 1.0000 C(20)-Si(1) 1.856(3) C(7)-O(4) 1.190(3) C(20)-H(20A) 0.9800 C(7)-O(1) 1.389(3) C(20)-H(20B) 0.9800 C(8)-O(5) 1.183(3) C(20)-H(20C) 0.9800 C(8)-O(1) 1.388(3) C(21)-C(23) 1.527(3) C(9)-O(2) 1.413(2) C(21)-C(22) 1.529(3) C(9)-H(9A) 0.9900 C(21)-C(24) 1.530(3) C(9)-H(9B) 0.9900 C(21)-Si(1) 1.887(2) C(10)-O(2) 1.420(2) C(22)-H(22A) 0.9800 C(10)-C(11) 1.512(3) C(22)-H(22B) 0.9800 C(10)-H(10A) 0.9900 C(22)-H(22C) 0.9800 C(10)-H(10B) 0.9900 C(23)-H(23A) 0.9800 C(11)-C(16) 1.390(3) C(23)-H(23B) 0.9800 C(11)-C(12) 1.394(3) C(23)-H(23C) 0.9800 C(12)-C(13) 1.391(3) C(24)-H(24A) 0.9800 C(12)-H(12) 0.9500 C(24)-H(24B) 0.9800 C(13)-C(14) 1.385(3) C(24)-H(24C) 0.9800 C(13)-H(13) 0.9500 O(6)-Si(1) 1.6537(16) C(14)-C(15) 1.389(3) 58

C(8)-C(1)-C(9) 108.04(16) O(1)-C(8)-C(1) 109.52(17) C(8)-C(1)-C(6) 103.77(17) O(2)-C(9)-C(1) 106.74(15) C(9)-C(1)-C(6) 112.75(17) O(2)-C(9)-H(9A) 110.4 C(8)-C(1)-C(2) 110.27(17) C(1)-C(9)-H(9A) 110.4 C(9)-C(1)-C(2) 110.67(17) O(2)-C(9)-H(9B) 110.4 C(6)-C(1)-C(2) 111.08(15) C(1)-C(9)-H(9B) 110.4 O(3)-C(2)-C(3) 113.97(17) H(9A)-C(9)-H(9B) 108.6 O(3)-C(2)-C(1) 108.22(15) O(2)-C(10)-C(11) 109.63(16) C(3)-C(2)-C(1) 111.38(17) O(2)-C(10)-H(10A) 109.7 O(3)-C(2)-H(2) 107.7 C(11)-C(10)-H(10A) 109.7 C(3)-C(2)-H(2) 107.7 O(2)-C(10)-H(10B) 109.7 C(1)-C(2)-H(2) 107.7 C(11)-C(10)-H(10B) 109.7 C(4)-C(3)-C(2) 118.54(19) H(10A)-C(10)-H(10B) 108.2 C(4)-C(3)-H(3) 120.7 C(16)-C(11)-C(12) 118.96(19) C(2)-C(3)-H(3) 120.7 C(16)-C(11)-C(10) 119.82(18) C(3)-C(4)-C(5) 118.02(18) C(12)-C(11)-C(10) 121.19(19) C(3)-C(4)-H(4) 121.0 C(13)-C(12)-C(11) 120.3(2) C(5)-C(4)-H(4) 121.0 C(13)-C(12)-H(12) 119.9 C(4)-C(5)-C(18) 113.38(17) C(11)-C(12)-H(12) 119.9 C(4)-C(5)-C(6) 106.94(17) C(14)-C(13)-C(12) 120.1(2) C(18)-C(5)-C(6) 113.22(18) C(14)-C(13)-H(13) 120.0 C(4)-C(5)-H(5) 107.7 C(12)-C(13)-H(13) 120.0 C(18)-C(5)-H(5) 107.7 C(13)-C(14)-C(15) 119.8(2) C(6)-C(5)-H(5) 107.7 C(13)-C(14)-H(14) 120.1 C(7)-C(6)-C(1) 103.97(17) C(15)-C(14)-H(14) 120.1 C(7)-C(6)-C(5) 112.31(17) C(16)-C(15)-C(14) 120.0(2) C(1)-C(6)-C(5) 113.70(17) C(16)-C(15)-H(15) 120.0 C(7)-C(6)-H(6) 108.9 C(14)-C(15)-H(15) 120.0 C(1)-C(6)-H(6) 108.9 C(15)-C(16)-C(11) 120.87(19) C(5)-C(6)-H(6) 108.9 C(15)-C(16)-H(16) 119.6 O(4)-C(7)-O(1) 119.5(2) C(11)-C(16)-H(16) 119.6 O(4)-C(7)-C(6) 130.2(2) O(3)-C(17)-H(17A) 109.5 O(1)-C(7)-C(6) 110.25(17) O(3)-C(17)-H(17B) 109.5 O(5)-C(8)-O(1) 120.70(19) H(17A)-C(17)-H(17B) 109.5 O(5)-C(8)-C(1) 129.7(2) O(3)-C(17)-H(17C) 109.5 59

H(17A)-C(17)-H(17C) 109.5 C(21)-C(22)-H(22B) 109.5 H(17B)-C(17)-H(17C) 109.5 H(22A)-C(22)-H(22B) 109.5 O(6)-C(18)-C(5) 109.39(17) C(21)-C(22)-H(22C) 109.5 O(6)-C(18)-H(18A) 109.8 H(22A)-C(22)-H(22C) 109.5 C(5)-C(18)-H(18A) 109.8 H(22B)-C(22)-H(22C) 109.5 O(6)-C(18)-H(18B) 109.8 C(21)-C(23)-H(23A) 109.5 C(5)-C(18)-H(18B) 109.8 C(21)-C(23)-H(23B) 109.5 H(18A)-C(18)-H(18B) 108.2 H(23A)-C(23)-H(23B) 109.5 Si(1)-C(19)-H(19A) 109.5 C(21)-C(23)-H(23C) 109.5 Si(1)-C(19)-H(19B) 109.5 H(23A)-C(23)-H(23C) 109.5 H(19A)-C(19)-H(19B) 109.5 H(23B)-C(23)-H(23C) 109.5 Si(1)-C(19)-H(19C) 109.5 C(21)-C(24)-H(24A) 109.5 H(19A)-C(19)-H(19C) 109.5 C(21)-C(24)-H(24B) 109.5 H(19B)-C(19)-H(19C) 109.5 H(24A)-C(24)-H(24B) 109.5 Si(1)-C(20)-H(20A) 109.5 C(21)-C(24)-H(24C) 109.5 Si(1)-C(20)-H(20B) 109.5 H(24A)-C(24)-H(24C) 109.5 H(20A)-C(20)-H(20B) 109.5 H(24B)-C(24)-H(24C) 109.5 Si(1)-C(20)-H(20C) 109.5 C(8)-O(1)-C(7) 111.00(16) H(20A)-C(20)-H(20C) 109.5 C(9)-O(2)-C(10) 112.30(15) H(20B)-C(20)-H(20C) 109.5 C(2)-O(3)-C(17) 112.32(16) C(23)-C(21)-C(22) 110.1(2) C(18)-O(6)-Si(1) 125.64(14) C(23)-C(21)-C(24) 109.2(2) O(6)-Si(1)-C(20) 109.59(12) C(22)-C(21)-C(24) 107.2(2) O(6)-Si(1)-C(19) 104.27(10) C(23)-C(21)-Si(1) 110.32(17) C(20)-Si(1)-C(19) 111.08(14) C(22)-C(21)-Si(1) 111.23(15) O(6)-Si(1)-C(21) 110.69(10) C(24)-C(21)-Si(1) 108.68(16) C(20)-Si(1)-C(21) 109.61(11) C(21)-C(22)-H(22A) 109.5 C(19)-Si(1)-C(21) 111.49(12)

______Symmetry transformations used to generate equivalent atoms:

Table 4. Anisotropic displacement parameters (Å2x 103)for sarpong29. The anisotropic displacement factor exponent takes the form: -22[ h2a*2U11 + ... + 2 h k a* b* U12 ] ______U11 U22 U33 U23 U13 U12 ______C(1) 26(1) 31(1) 23(1) -1(1) 1(1) 2(1) C(2) 26(1) 30(1) 26(1) 1(1) 0(1) 1(1) C(3) 27(1) 31(1) 28(1) -4(1) 1(1) -2(1) C(4) 29(1) 39(1) 24(1) -4(1) -2(1) -2(1) C(5) 30(1) 34(1) 22(1) 2(1) -1(1) 1(1) C(6) 32(1) 29(1) 23(1) -1(1) 0(1) -1(1) C(7) 32(1) 37(1) 26(1) -5(1) 1(1) -7(1) C(8) 28(1) 34(1) 27(1) -6(1) -1(1) 0(1) C(9) 28(1) 32(1) 22(1) 1(1) -2(1) 3(1) C(10) 30(1) 33(1) 23(1) -2(1) 0(1) 1(1) C(11) 27(1) 26(1) 27(1) -2(1) 1(1) -2(1) C(12) 33(1) 32(1) 26(1) -1(1) 3(1) 0(1) C(13) 34(1) 37(1) 27(1) 1(1) -2(1) 3(1) C(14) 30(1) 35(1) 35(1) -1(1) -1(1) 4(1) C(15) 30(1) 32(1) 32(1) -4(1) 6(1) 0(1) C(16) 31(1) 31(1) 26(1) -1(1) 1(1) -4(1) C(17) 40(1) 36(1) 38(1) 7(1) -2(1) -8(1) C(18) 45(1) 34(1) 24(1) 3(1) -2(1) 2(1) C(19) 76(2) 46(2) 35(1) -9(1) -14(1) 17(1) C(20) 39(1) 75(2) 43(1) 1(1) 10(1) 2(1) C(21) 37(1) 29(1) 32(1) 6(1) 0(1) 2(1) C(22) 45(1) 49(1) 26(1) 5(1) 4(1) -2(1) C(23) 92(2) 51(2) 45(2) 15(1) 12(2) 31(2) C(24) 45(2) 60(2) 61(2) 6(1) 4(1) -16(1) O(1) 28(1) 43(1) 31(1) -3(1) 2(1) 3(1) O(2) 29(1) 40(1) 23(1) -4(1) -1(1) 8(1) O(3) 33(1) 32(1) 32(1) 7(1) -5(1) -2(1) O(4) 40(1) 55(1) 32(1) 0(1) 8(1) -9(1) O(5) 32(1) 44(1) 32(1) 2(1) -6(1) 8(1) O(6) 50(1) 32(1) 30(1) 4(1) -9(1) 3(1) Si(1) 37(1) 34(1) 24(1) 1(1) -2(1) 5(1) 61

Table 5. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 103) for sarpong29. ______x y z U(eq) ______

H(2) 1694 -700 7663 33 H(3) 3018 -1388 6393 35 H(4) 2761 -596 5435 37 H(5) 1770 158 6706 35 H(6) 4775 502 7451 34 H(9A) 4013 -422 9202 33 H(9B) 5159 174 8988 33 H(10A) 2887 817 9524 35 H(10B) 1762 242 9827 35 H(12) 12 884 7785 36 H(13) -2893 1408 7465 40 H(14) -4708 1672 8594 40 H(15) -3581 1428 10048 37 H(16) -696 905 10366 35 H(17A) 553 -1540 8145 57 H(17B) 1943 -2079 8499 57 H(17C) 1535 -1951 7467 57 H(18A) 4188 485 5396 42 H(18B) 1898 590 5341 42 H(19A) 2442 2112 7400 81 H(19B) 2418 2664 6737 81 H(19C) 4355 2283 6971 81 H(20A) -834 1365 5314 78 H(20B) -1169 1960 5857 78 H(20C) -693 1342 6362 78 H(22A) 827 1566 4059 60 H(22B) 2950 1280 4201 60 H(22C) 2511 1837 3552 60 H(23A) 2058 2846 4132 94 H(23B) 2149 2958 5167 94 62

H(23C) 334 2619 4652 94 H(24A) 5630 1804 5070 84 H(24B) 5352 2479 5377 84 H(24C) 5290 2326 4355 84 ______

X-Ray Crystallography Data for Amide 2.46

A colorless plate 0.040 x 0.030 x 0.020 mm in size was mounted on a Cryoloop with Paratone oil. Data were collected in a nitrogen gas stream at 100(2) K using phi and omega scans. Crystal- to-detector distance was 60 mm and exposure time was 5 seconds per frame using a scan width of 2.0°. Data collection was 98.4% complete to 67.000° in . A total of 29826 reflections were collected covering the indices, -10<=h<=10, -11<=k<=11, -16<=l<=16. 3631 reflections were found to be symmetry independent, with an Rint of 0.0239. Indexing and unit cell refinement indicated a primitive, triclinic lattice. The space group was found to be P -1 (No. 2). The data were integrated using the Bruker SAINT software program and scaled using the SADABS software program. Solution by iterative methods (SHELXT) produced a complete heavy-atom phasing model consistent with the proposed structure. All non-hydrogen atoms were refined anisotropically by full-matrix least-squares (SHELXL-2013). All hydrogen atoms were placed using a riding model. Their positions were constrained relative to their parent atom using the appropriate HFIX command in SHELXL-2013.

Table 1. Crystal data and structure refinement for sarpong67. X-ray ID sarpong67 Sample/notebook ID JJPIV-005 Empirical formula C22 H31 N O5 Formula weight 389.48 Temperature 100(2) K Wavelength 1.54178 Å Crystal system Triclinic Space group P -1 Unit cell dimensions a = 9.0812(5) Å = 83.103(3)°. b = 9.3858(5) Å = 76.197(2)°. c = 13.5396(7) Å  = 64.565(2)°. Volume 1011.88(10) Å3 Z 2 Density (calculated) 1.278 Mg/m3 Absorption coefficient 0.730 mm-1 F(000) 420 Crystal size 0.040 x 0.030 x 0.020 mm3 Crystal color/habit colorless plate Theta range for data collection 3.362 to 68.278°. Index ranges -10<=h<=10, -11<=k<=11, -16<=l<=16 Reflections collected 29826 Independent reflections 3631 [R(int) = 0.0239] Completeness to theta = 67.000° 98.4 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.929 and 0.882 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3631 / 0 / 258 Goodness-of-fit on F2 1.038 Final R indices [I>2sigma(I)] R1 = 0.0337, wR2 = 0.0857 R indices (all data) R1 = 0.0368, wR2 = 0.0885 Extinction coefficient n/a Largest diff. peak and hole 0.330 and -0.180 e.Å-3

Table 2. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for sarpong67. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. ______x y z U(eq) ______C(1) 6792(1) 3162(1) 3273(1) 16(1) C(2) 6146(1) 4266(1) 2372(1) 16(1) C(3) 4269(2) 5406(1) 2496(1) 18(1) C(4) 3789(2) 6991(1) 2974(1) 21(1) C(5) 4954(2) 7761(1) 2442(1) 22(1) C(6) 6727(2) 6690(1) 2542(1) 18(1) C(7) 7335(2) 5094(1) 2016(1) 17(1) C(8) 8895(2) 3984(1) 2400(1) 18(1) C(9) 6658(2) 1573(1) 3312(1) 18(1) C(10) 7603(2) 557(1) 2382(1) 18(1) C(11) 6838(2) 719(1) 1575(1) 19(1) C(12) 7685(2) -215(1) 719(1) 20(1) C(13) 9313(2) -1333(1) 658(1) 22(1) C(14) 10071(2) -1511(2) 1472(1) 23(1) C(15) 9236(2) -586(1) 2324(1) 21(1) C(16) 7517(2) -995(2) -847(1) 26(1) C(17) 3048(2) 4704(2) 3041(1) 22(1) C(18) 6627(2) 7606(2) 4144(1) 28(1) C(19) 7789(2) 5343(1) 880(1) 20(1) C(20) 7203(2) 5031(2) 169(1) 25(1) C(21) 9723(2) 1950(2) 3710(1) 23(1) C(22) 9830(2) 2876(2) 4517(1) 29(1) N(1) 8551(1) 2931(1) 3066(1) 17(1) O(1) 5967(1) 3803(1) 4250(1) 19(1) O(2) 6792(1) 68(1) -20(1) 28(1) O(3) 3284(1) 3344(1) 2544(1) 27(1) O(4) 6834(1) 6313(1) 3592(1) 19(1) O(5) 10246(1) 4078(1) 2151(1) 22(1) ______

Table 3. Bond lengths [Å] and angles [°] for sarpong67. ______C(1)-O(1) 1.4157(14) C(12)-C(13) 1.3868(18) C(1)-N(1) 1.4767(15) C(13)-C(14) 1.3905(18) C(1)-C(9) 1.5413(16) C(13)-H(13) 0.9500 C(1)-C(2) 1.5567(16) C(14)-C(15) 1.3847(18) C(2)-C(7) 1.5448(15) C(14)-H(14) 0.9500 C(2)-C(3) 1.5546(16) C(15)-H(15) 0.9500 C(2)-H(2) 1.0000 C(16)-O(2) 1.4269(15) C(3)-C(17) 1.5260(16) C(16)-H(16A) 0.9800 C(3)-C(4) 1.5369(16) C(16)-H(16B) 0.9800 C(3)-H(3) 1.0000 C(16)-H(16C) 0.9800 C(4)-C(5) 1.5259(17) C(17)-O(3) 1.4250(15) C(4)-H(4A) 0.9900 C(17)-H(17A) 0.9900 C(4)-H(4B) 0.9900 C(17)-H(17B) 0.9900 C(5)-C(6) 1.5177(17) C(18)-O(4) 1.4214(15) C(5)-H(5A) 0.9900 C(18)-H(18A) 0.9800 C(5)-H(5B) 0.9900 C(18)-H(18B) 0.9800 C(6)-O(4) 1.4391(14) C(18)-H(18C) 0.9800 C(6)-C(7) 1.5530(16) C(19)-C(20) 1.3201(18) C(6)-H(6) 1.0000 C(19)-H(19) 0.9500 C(7)-C(19) 1.5116(16) C(20)-H(20A) 0.9500 C(7)-C(8) 1.5224(16) C(20)-H(20B) 0.9500 C(8)-O(5) 1.2310(15) C(21)-N(1) 1.4657(15) C(8)-N(1) 1.3435(15) C(21)-C(22) 1.5202(18) C(9)-C(10) 1.5164(16) C(21)-H(21A) 0.9900 C(9)-H(9A) 0.9900 C(21)-H(21B) 0.9900 C(9)-H(9B) 0.9900 C(22)-H(22A) 0.9800 C(10)-C(11) 1.3894(17) C(22)-H(22B) 0.9800 C(10)-C(15) 1.3988(18) C(22)-H(22C) 0.9800 C(11)-C(12) 1.3940(17) O(1)-H(1) 0.8400 C(11)-H(11) 0.9500 O(3)-H(3A) 0.8400 C(12)-O(2) 1.3660(15)

O(1)-C(1)-N(1) 110.03(9) C(19)-C(7)-C(8) 109.37(10) O(1)-C(1)-C(9) 105.16(9) C(19)-C(7)-C(2) 115.73(10) N(1)-C(1)-C(9) 111.13(9) C(8)-C(7)-C(2) 103.25(9) O(1)-C(1)-C(2) 114.87(9) C(19)-C(7)-C(6) 108.59(9) N(1)-C(1)-C(2) 102.13(9) C(8)-C(7)-C(6) 105.61(9) C(9)-C(1)-C(2) 113.65(9) C(2)-C(7)-C(6) 113.63(9) C(7)-C(2)-C(3) 113.80(9) O(5)-C(8)-N(1) 125.87(11) C(7)-C(2)-C(1) 105.05(9) O(5)-C(8)-C(7) 124.51(11) C(3)-C(2)-C(1) 120.03(10) N(1)-C(8)-C(7) 109.60(10) C(7)-C(2)-H(2) 105.6 C(10)-C(9)-C(1) 115.86(9) C(3)-C(2)-H(2) 105.6 C(10)-C(9)-H(9A) 108.3 C(1)-C(2)-H(2) 105.6 C(1)-C(9)-H(9A) 108.3 C(17)-C(3)-C(4) 109.21(10) C(10)-C(9)-H(9B) 108.3 C(17)-C(3)-C(2) 115.46(10) C(1)-C(9)-H(9B) 108.3 C(4)-C(3)-C(2) 114.43(9) H(9A)-C(9)-H(9B) 107.4 C(17)-C(3)-H(3) 105.6 C(11)-C(10)-C(15) 118.46(11) C(4)-C(3)-H(3) 105.6 C(11)-C(10)-C(9) 120.29(11) C(2)-C(3)-H(3) 105.6 C(15)-C(10)-C(9) 121.24(11) C(5)-C(4)-C(3) 111.34(10) C(10)-C(11)-C(12) 120.93(11) C(5)-C(4)-H(4A) 109.4 C(10)-C(11)-H(11) 119.5 C(3)-C(4)-H(4A) 109.4 C(12)-C(11)-H(11) 119.5 C(5)-C(4)-H(4B) 109.4 O(2)-C(12)-C(13) 124.57(11) C(3)-C(4)-H(4B) 109.4 O(2)-C(12)-C(11) 114.97(11) H(4A)-C(4)-H(4B) 108.0 C(13)-C(12)-C(11) 120.46(12) C(6)-C(5)-C(4) 109.64(10) C(12)-C(13)-C(14) 118.61(12) C(6)-C(5)-H(5A) 109.7 C(12)-C(13)-H(13) 120.7 C(4)-C(5)-H(5A) 109.7 C(14)-C(13)-H(13) 120.7 C(6)-C(5)-H(5B) 109.7 C(15)-C(14)-C(13) 121.23(12) C(4)-C(5)-H(5B) 109.7 C(15)-C(14)-H(14) 119.4 H(5A)-C(5)-H(5B) 108.2 C(13)-C(14)-H(14) 119.4 O(4)-C(6)-C(5) 111.21(10) C(14)-C(15)-C(10) 120.29(12) O(4)-C(6)-C(7) 106.39(9) C(14)-C(15)-H(15) 119.9 C(5)-C(6)-C(7) 110.61(10) C(10)-C(15)-H(15) 119.9 O(4)-C(6)-H(6) 109.5 O(2)-C(16)-H(16A) 109.5 C(5)-C(6)-H(6) 109.5 O(2)-C(16)-H(16B) 109.5 C(7)-C(6)-H(6) 109.5 H(16A)-C(16)-H(16B) 109.5 68

O(2)-C(16)-H(16C) 109.5 H(20A)-C(20)-H(20B) 120.0 H(16A)-C(16)-H(16C) 109.5 N(1)-C(21)-C(22) 113.29(11) H(16B)-C(16)-H(16C) 109.5 N(1)-C(21)-H(21A) 108.9 O(3)-C(17)-C(3) 111.89(10) C(22)-C(21)-H(21A) 108.9 O(3)-C(17)-H(17A) 109.2 N(1)-C(21)-H(21B) 108.9 C(3)-C(17)-H(17A) 109.2 C(22)-C(21)-H(21B) 108.9 O(3)-C(17)-H(17B) 109.2 H(21A)-C(21)-H(21B) 107.7 C(3)-C(17)-H(17B) 109.2 C(21)-C(22)-H(22A) 109.5 H(17A)-C(17)-H(17B) 107.9 C(21)-C(22)-H(22B) 109.5 O(4)-C(18)-H(18A) 109.5 H(22A)-C(22)-H(22B) 109.5 O(4)-C(18)-H(18B) 109.5 C(21)-C(22)-H(22C) 109.5 H(18A)-C(18)-H(18B) 109.5 H(22A)-C(22)-H(22C) 109.5 O(4)-C(18)-H(18C) 109.5 H(22B)-C(22)-H(22C) 109.5 H(18A)-C(18)-H(18C) 109.5 C(8)-N(1)-C(21) 120.38(10) H(18B)-C(18)-H(18C) 109.5 C(8)-N(1)-C(1) 114.19(10) C(20)-C(19)-C(7) 127.49(11) C(21)-N(1)-C(1) 123.47(10) C(20)-C(19)-H(19) 116.3 C(1)-O(1)-H(1) 109.5 C(7)-C(19)-H(19) 116.3 C(12)-O(2)-C(16) 117.09(10) C(19)-C(20)-H(20A) 120.0 C(17)-O(3)-H(3A) 109.5 C(19)-C(20)-H(20B) 120.0 C(18)-O(4)-C(6) 113.72(9)

______Symmetry transformations used to generate equivalent atoms:

Table 4. Anisotropic displacement parameters (Å2x 103) for sarpong67. The anisotropic displacement factor exponent takes the form: -22[ h2 a*2U11 + ... + 2 h k a* b* U12 ] ______U11 U22 U33 U23 U13 U12 ______C(1) 14(1) 19(1) 17(1) -2(1) -2(1) -8(1) C(2) 14(1) 18(1) 17(1) -2(1) -3(1) -8(1) C(3) 14(1) 21(1) 20(1) -1(1) -4(1) -6(1) C(4) 15(1) 20(1) 26(1) -2(1) -4(1) -4(1) C(5) 22(1) 18(1) 24(1) -2(1) -4(1) -7(1) C(6) 19(1) 19(1) 19(1) 0(1) -3(1) -11(1) C(7) 15(1) 18(1) 18(1) -2(1) -2(1) -8(1) C(8) 17(1) 19(1) 17(1) -5(1) -2(1) -9(1) C(9) 18(1) 19(1) 19(1) 1(1) -3(1) -10(1) C(10) 18(1) 16(1) 22(1) 1(1) -1(1) -11(1) C(11) 17(1) 17(1) 25(1) -1(1) -3(1) -8(1) C(12) 23(1) 19(1) 22(1) 0(1) -4(1) -12(1) C(13) 23(1) 19(1) 23(1) -4(1) 1(1) -10(1) C(14) 17(1) 20(1) 30(1) -3(1) -3(1) -6(1) C(15) 20(1) 21(1) 25(1) 1(1) -6(1) -10(1) C(16) 35(1) 23(1) 22(1) -4(1) -6(1) -11(1) C(17) 14(1) 24(1) 26(1) -5(1) -3(1) -8(1) C(18) 43(1) 27(1) 24(1) -2(1) -7(1) -22(1) C(19) 19(1) 19(1) 21(1) 0(1) -1(1) -9(1) C(20) 28(1) 28(1) 19(1) 1(1) -3(1) -14(1) C(21) 19(1) 24(1) 26(1) 3(1) -9(1) -8(1) C(22) 27(1) 39(1) 26(1) 0(1) -10(1) -16(1) N(1) 14(1) 19(1) 19(1) -1(1) -4(1) -7(1) O(1) 21(1) 19(1) 17(1) -3(1) -1(1) -10(1) O(2) 29(1) 26(1) 27(1) -8(1) -10(1) -5(1) O(3) 16(1) 28(1) 40(1) -10(1) -6(1) -9(1) O(4) 22(1) 19(1) 18(1) -2(1) -3(1) -11(1) O(5) 15(1) 27(1) 25(1) -3(1) -2(1) -12(1) ______

Table 5. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for sarpong67. ______x y z U(eq) ______

H(2) 6384 3549 1809 19 H(3) 4064 5671 1790 22 H(4A) 2629 7708 2926 26 H(4B) 3838 6818 3704 26 H(5A) 4898 7951 1714 26 H(5B) 4601 8790 2752 26 H(6) 7480 7219 2223 22 H(9A) 7068 959 3912 22 H(9B) 5466 1788 3415 22 H(11) 5722 1477 1607 23 H(13) 9899 -1964 73 26 H(14) 11181 -2281 1442 28 H(15) 9776 -729 2873 26 H(16A) 8517 -885 -1247 40 H(16B) 6711 -748 -1280 40 H(16C) 7822 -2080 -583 40 H(17A) 3197 4413 3749 26 H(17B) 1893 5509 3067 26 H(18A) 7390 8070 3776 43 H(18B) 6873 7235 4819 43 H(18C) 5475 8403 4217 43 H(19) 8590 5774 651 24 H(20A) 6399 4598 353 30 H(20B) 7584 5238 -526 30 H(21A) 10845 1426 3274 27 H(21B) 9376 1115 4048 27 H(22A) 10179 3702 4188 43 H(22B) 10645 2163 4912 43 H(22C) 8734 3362 4970 43 H(1) 5975 4690 4270 28 71

H(3A) 2370 3452 2433 41 ______

Chapter 3. Total Synthesis of Cossonidine: A Benzyne-Insertion Route toward Hetisine- type C20-Diterpenoid Alkaloids

3.1 Introduction Within the C20-diterpenoid alkaloids, the hetisine-type is the most prevalent, with over 120 known members.1 Featuring a tertiary amine embedded in a heptacyclic skeleton, the hetisine-type also possesses one of the most complex skeletons of the C20-diterpenoid alkaloids. As discussed in Chapter 1, the hetisine-type alkaloids are closely related to the hetidine-type and the atisine-type alkaloids. Starting from the atisine-type core, formation of the C14–C20 bond provides the hetidine-type core, and subsequent N–C6 bond formation converts the hetidine-type core into the hetisine-type core.1a Initial studies by Okamoto and coworkers suggested that hetidine-type alkaloids could be directly converted to hetisine-type alkaloids such as 3.2 (albeit in minimal yield) via chloramine intermediate 3.1 through a Hofmann-Löffler-Freytag-type reaction (Scheme 3-1).2 However, recent efforts from the Baran lab could not realize this transformation in a related system.3

Scheme 3-1. Conversion of the hetidine skeleton to the hetisine skeleton by Okamoto

As a testament to the increased complexity of the hetisine-type alkaloids, only two total syntheses of this skeleton have been reported, both of which are syntheses of the mono- hydroxylated alkaloid nominine (3.3),4,5 as discussed in Chapter 1. While the synthesis of nominine developed by Gin5 is particularly elegant, the route only permits oxygenation at a single position, on the [2.2.2]bicycle. For our synthesis, we desired a synthetic route that would readily install oxygenation on both the [2.2.2]bicycle and the A-ring (see labeling on 3.4, Figure 3-1), both of which are oxygenated in many hetisine-type natural products. This is especially relevant given the important biological activities of guan-fu base A (3.4), currently in use in China for the treatment of arrhythmia, which bears A-ring oxygenation at C2 in addition to 3 sites of oxygenation on the [2.2.2]bicycle.6 Thus, we sought to develop a de novo synthesis that would directly target the hetisine-type core bearing oxygenation on both the A ring and the [2.2.2]bicycle. In order to validate our initial approach, we selected cossonidine (3.5) as our first target, a hetisine-type diterpenoid alkaloid bearing hydroxyl groups on C1 and C15.

Figure 3-1. Selected hetisine-type C20-diterpenoid alkaloids

Cossonidine was isolated in 1996 by two independent research groups. A team led by de la Fuente isolated cossonidine from Delphinium cossonianum and Delphinium cardiopetalum,7 while Pelletier and coworkers isolated the same natural product from Delphinium davisii, terming this compound davisine.8 To simplify this naming disparity, this compound will hereafter be referred to as cossonidine.

3.2 Retrosynthesis and Previous Work toward the Heptacyclic Core of Cossonidine Retrosynthetically, we envisioned forming the [2.2.2]bicycle late-stage from pentacycle 3.6, bearing an arene and a vinyl group (Scheme 3-2). In the forward sense, a Birch reduction followed by an intramolecular Diels–Alder reaction would forge the [2.2.2]bicycle.5 Subsequent functional group manipulations to deprotect and invert the C1 hydroxyl group and install the allylic alcohol would provide cossonidine (3.5). Continuing with our network analysis approach, in which caged systems are disconnected to all-fused systems,9 we envisioned subsequent C–N bond forming reactions would allow for the synthesis of pentacycle 3.6 from 6-7-6 tricycle 3.7. In order to forge this all-fused tricyclic core, we sought to take advantage of benzyne-insertion chemistry developed by the Stoltz lab in which an aryne is formally inserted into the carbon- carbon bond of a β-ketoester.10 This reaction would require the syntheses of aryne precursor 3.8 and β-ketoester 3.9, which can be accessed through a Diels–Alder reaction of diene 3.10 and dienophile 3.11.

Scheme 3-2. Retrosynthetic analysis of cossonidine

Initial exploration of this synthetic route was performed by a former graduate student in the Sarpong lab, Jessica Kisunzu, aided by Dr. Toshihiro Kiho, Dr. Ethan Fisher, Kyle Clagg, and Dr. Terry Lebold. Scheme 3-3 illustrates the route developed by this team, as reported in Jessica Kisunzu’s Ph.D. dissertation.11 Synthesis of diene 3.10 was carried out as previously described (Chapter 2), and dienophile 3.11 could be prepared in only 2 steps. The Diels–Alder reaction between these two substrates provided adduct 3.12. This product could then be elaborated to β-ketoester 3.9 through a 5-step sequence involving a series of reductions, re- oxidation, methylenation, and allylcarboxylation. Successful application of the Stoltz benzyne acyl-alkylation reaction with aryne precursor 3.8 (synthesized in 5 steps from 4-methoxyphenol) provided 6-7-6 tricycle 3.13. Subsequent deallylation, decarboxylative elimination, and silyl ether cleavage were followed by a 3-step nitrile formation and subsequent methylation to provide tricycle 3.7. At this stage, reduction of the cyano group was followed by a reductive cyclization with LiAlH4 to form the N–C20 bond, followed by a light-mediated, formal hydroamination to forge the N–C6 bond, which afforded tertiary amine 3.6. Birch reduction followed by an intramolecular Diels–Alder reaction constructed the [2.2.2]bicycle of 3.15, the most advanced intermediate achieved. The remaining work involved subsequent deprotection and inversion of the C1-hydroxyl group and methylenation followed by allylic oxygenation to install the allylic alcohol to complete the total synthesis of cossonidine (3.5).

Scheme 3-3. Previous work toward cossonidine in the Sarpong group

My tasks upon inheriting this project were reproducing and optimizing this initial chemistry (i.e., through the synthesis of [2.2.2]bicycle 3.15), and developing the chemistry to complete the final functional group manipulations and complete the total synthesis of cossonidine. While much of the early chemistry proceeded without significant issues, several steps required further development and optimization. These improvements, along with a more thorough discussion of the entire route, are presented in the next section.

3.3 Optimization of the Initial Route to the Heptacyclic Core Starting from methyl 2-oxocyclopentanecarboxylate (3.16), α-selenation with phenylselenium bromide followed by an oxidative elimination with hydrogen peroxide provides dienophile 3.11 in effectively quantitative yield (Scheme 3-4).12 Due to the relative instability of this compound, this reagent was always prepared fresh and used immediately in the Diels–Alder reaction. Heating this dienophile at 100 °C in toluene with diene 3.10, prepared as previously described in Chapter 2, provides desired endo adduct 3.12 in 71% yield. Hydrogenation of the alkene, mediated by palladium on carbon, proceeds in 98% yield to afford 3.17, which is followed by a global reduction of the ester and ketone groups with LiAlH4 to provide diol 3.18. At this stage, a Ley oxidation13 is employed to access ketoaldehyde 3.19, which was subjected to a methylenation protocol developed by the Lebel group,14 installing the requisite vinyl group and producing vinyl ketone 3.20 in 72% yield over 3 steps. Deprotonation with LiHMDS followed by addition of allyl cyanoformate15 provides β-ketoester 3.9 in 88% yield as an inconsequential 1:1 mixture of diastereomers.

Scheme 3-4. Synthesis of β-ketoester 3.9

Benzyne precursor 3.8 was prepared following an analogous procedure to that reported by Garg.16 Starting from 4-methoxyphenol (3.21), a carbamate synthesis with isopropylisocyanate provides 3.22 (Scheme 3-5). Sequential ortho-lithiations are then employed to install the requisite silyl and bromo substituents. First, nBuLi and TMSCl are used to install the trimethylsilyl group necessary for facile aryne formation (3.23). Next, sBuLi and dibromoethane are employed to install the bromine atom on 3.24. While not apparently required in our synthesis of cossonidine, this bromine atom is critical for controlling the regioselectivity of the aryne insertion reaction, as observed and rationalized by Garg and Houk.17 Furthermore, this bromine atom provides an additional functional group handle for possible late-stage derivatization of the natural product. Carbamate cleavage with diethylamide to afford phenol 3.25 was then followed by triflate formation to provide aryne precursor 3.8 in 83% yield over 5 steps.

Scheme 3-5. Synthesis of benzyne precursor 3.8

With only minor modifications, the benzyne acyl-alkylation reaction proceeded as described by Stoltz,10 providing tricycle 3.13 in 41% yield (Scheme 3-6). According to the proposed mechanism,10 cesium fluoride leads to generation of the highly reactive benzyne intermediate, which is attacked by the enolate of the β-ketoester with high regioselectivity due to the presence of the bromine atom on the aryne to afford 3.26. Subsequent 1,2-addition of the resultant aryl anion provides strained cylobutanoxide intermediate 3.27. Upon collapse of the tetrahedral intermediate, fragmentation of the internal C–C bond followed by diastereoselective protonation affords ring-expanded tricycle 3.13. While the yields are modest, to the best of our knowledge, this reaction represents the most complex example of an aryne acyl-alkylation reaction reported to date.18 Currently, this reaction is run in 20 mL microwave vials, which has helped to improve the consistency and reproducibility of the reaction. This does, however, present a challenge to the large throughput of material. Further optimization may be required in order to render this reaction truly scalable, while minimizing the time and effort required.

Scheme 3-6. Benzyne acyl-alkylation reaction and proposed mechanism

With 6-7-6 tricycle 3.13 in hand, deallylation proceeds in 93% yield using Pd(PPh3)4 and phenylsilane19 to afford carboxylic acid 3.28 (Scheme 3-7). Improvements in both yield and reproducibility were then achieved for the subsequent decarboxylative elimination reaction. Following a procedure reported by Gandelman,20 this reaction was initially reported to proceed in 55% yield over the two steps of deallylation and elimination. Mechanistically, we suspect that the decarboxylation proceeds as reported by Gandelman to afford the intermediate alkyl iodide, which spontaneously eliminates in the reaction vessel to directly afford the styrenyl double bond. Despite the anticipated moderate yields, in my hands, initial attempts to run this reaction resulted in only 22% and 26% isolated yields for this decarboxylative elimination. After several trials, a modified procedure involving positioning the light source 0.2 m from the reaction, switching the reaction vessel to a flame-dried 10 mL Pyrex reaction tube, sparging the reaction mixture with argon for 30 minutes, and decreasing the reaction time from 2 h to 1 h resulted in a more consistent and higher-yielding reaction, providing elimination product 3.29 in 74% isolated yield. Once again, however, we run into difficulties in scale-up due to the relatively small size of the reaction vessels employed, an issue common in many photochemical reactions. While the use of larger reaction vessels has not been thoroughly explored, flow chemistry may provide a more promising option for further reaction optimization.21

Scheme 3-7. Deallylation and decarboxylative elimination

At this stage in the reported route, a TBAF-mediated silyl ether cleavage was followed by DMP oxidation22 to form the corresponding aldehyde (3.30, Scheme 3-8). This aldehyde was converted into the corresponding oxime with hydroxylamine and subjected to elimination with acetic anhydride to afford nitrile 3.31. This sequence was reported to proceed in 56% yield over these 4 steps. While the silyl ether cleavage to produce primary alcohol 3.14 proceeded without event, significant challenges were encountered attempting to reproduce the 3-step nitrile formation sequence. The DMP oxidation alone only proceeded in 54% yield on 46 mg scale, with yields dropping to 27% on 104 mg scale. Furthermore, oxime formation was not reproducible in my hands, mainly resulting in low to negligible yields for this reaction. Attempting the oxime formation-elimination in tandem, only a 44% yield for the nitrile was obtained on 25 mg scale.

Scheme 3-8. Previously developed 4-step route to nitrile 3.31

Investigating alternate protocols, a one-step procedure for converting aldehyde 3.30 into nitrile 3.31 using hydroxylamine hydrochloride in DMSO at 90 °C provided nitrile 3.31 in a slightly higher 51% yield.23 While this yield would be acceptable for continuing with the synthesis, a more efficient oxidation from alcohol 3.14 to aldehyde 3.30 was required. Given the numerous issues encountered in carrying out this 3-step process, a method to directly convert alcohol 3.14 to nitrile 3.31 was sought. Following a procedure reported by Togo,24 subjecting primary alcohol 3.14 to aqueous ammonia mediated by either molecular iodine or DIH resulted only in minimal conversion to nitrile 3.31, with primarily starting material recovered. The greatest success was achieved employing a recently-published procedure from Vatèle for the direct, 1-step conversion of primary alcohols to nitriles employing TEMPO, PIDA, and ammonium acetate in a 9:1 mixture of acetonitrile and water.25 Yields of up to 79% were obtained with this procedure, with further optimization performed by Dr. Louis Morrill, a postdoctoral scholar in our group who joined the project to help with scale-up and reaction optimization. In the final version of this protocol, we were able to increase the yield of nitrile formation to 96%, cutting two steps out of the reaction sequence in the process (Scheme 3-9).

Scheme 3-9. Optimized 2-step route to nitrile 3.31

With a reliable and scalable synthesis of nitrile 3.31 in hand, I was then able to examine the conditions for the methylation reaction, which required significant screening by Dr. Toshihiro Kiho in order to achieve methylation from the desired face in acceptable yields. After slight adjustments to the equivalents of LiHMDS and iodomethane employed, methylated product 3.7 could be produced reliably in 58% yield (Scheme 3-10).

Scheme 3-10. Methylation reaction of nitrile 3.7

Looking toward the requisite C–N bond forming reactions to assemble the azabicycle, we next needed to achieve a reduction of the cyano group in 3.7 to the corresponding primary amine, followed by a reductive cascade reaction using LiAlH4 to forge the N–C20 bond and remove the bromine atom that had originally been installed to aid in the regioselectivity of the benzyne insertion reaction. At the outset, this sequence was reported to proceed in only 37% yield over these 2 steps (Scheme 3-11) and a thorough evaluation of these conditions to improve the yield and reproducibility of these reactions was undertaken. The first step in this sequence is the chemoselective reduction of the nitrile group in 3.7 in the presence of the ketone carbonyl and the vinyl and styrenyl double bonds. While a complete global reduction of this molecule with LiAlH4 was initially attempted, incomplete nitrile reduction was theorized to significantly impede reaction progress, leading to undesired reaction products that could not be advanced. After exploring several options, the use of in situ generated cobalt boride26 was identified by Jessica to facilitate the desired nitrile reduction, although significant amounts of off-target reductions were also observed. Nevertheless, treatment of this reaction mixture with LiAlH4 then allowed secondary amine 3.32 to be isolated, albeit in low, variable yields.

Scheme 3-11. Previous, unoptimized synthesis of secondary amine 3.32

Having identified the nitrile reduction as the most problematic step in this sequence, a deeper investigation into the cobalt boride literature was undertaken. While detailed studies of cobalt boride are relatively scarce, Ganem and coworkers reported on a series of mechanistic experiments in 1982.27 As a result of their studies, these authors concluded that cobalt boride acts by coordinating to various functional groups, catalyzing their reduction by external NaBH4, or some other competent reducing agent. Looking to explore the feasibility of transient quantities of surface-generated BH3 serving as a reducing agent, they explored using pre-formed cobalt boride in combination with amine-borane complexes, which are stable at ambient temperature but thermally dissociate into free BH3. Using tert-butylamine–borane (TAB), which is typically unreactive in the presence of nitriles, in combination with cobalt boride, they observed facile nitrile reduction to the corresponding primary amine (Table 3-1). Interestingly, alkenes and alkynes were found to react more slowly with this reagent system than the standard in situ generation with CoCl2 and NaBH4. Notably, while there is a qualitative rate comparison presented in the paper, no molecules bearing both a nitrile and additional units of unsaturation were reported.

Table 3-1. Substrates examined by Ganem in cobalt boride reduction studies

Looking to take advantage of the reported rate differences between nitrile and alkene reductions with this reagent system, we began investigating application of this protocol to methylated nitrile 3.7 (Scheme 3-12). Initial results were very encouraging, providing amino ketone 3.33 along with recovered starting material. Developing a reliable reaction protocol from the relatively sparse experimental information given in the original report ultimately led to a very efficient, completely chemoselective, reduction of the cyano group to the primary amine. Some considerations key to the success and reproducibility of this reaction include using freshly prepared cobalt boride and performing the reaction in a sealed vessel (microwave vials were employed for this purpose) under an atmosphere of nitrogen. After work-up, crude primary amine 3.33 was dried by azeotropic distillation with benzene (key for achieving full conversion in the subsequent reduction cascade) and subjected directly to LiAlH4 in THF under reflux. Under these conditions, the arene is debrominated, the ketone carbonyl is reduced, and the N– C20 bond is formed, providing 3.32. Based on evidence reported by Baik, we propose the intermediacy of a p-quinone methide in facilitating C–N bond formation.28 While secondary amine 3.32 could be isolated, in practice this crude material was directly advanced to the subsequent light-mediated hydroamination reaction, following the protocol reported by the Trost lab in their synthesis of morphine.29 Through this sequence, we can advance fused 6-7-6 tricycle 3.7 to pentacyclic azabicycle 3.6 in 71% yield over 3 steps with only a single purification.

Scheme 3-12. Optimized synthesis of tertiary amine 3.6

The final reported transformation is a 2-step construction of the [2.2.2]bicycle, which completes the heptacyclic core of the hetisine-type diterpenoid alkaloids. Gin had previously demonstrated the use of a Birch reduction/Diels–Alder cycloaddition to accomplish this transformation in his synthesis of nominine (3.3), smoothly converting vinyl arene 3.34 to [2.2.2]bicycle 3.36 in 76% yield over 2 steps (Scheme 3-13).5 Given that our system is identical to Gin’s intermediate except for the equatorial methoxy group at C1, Jessica had previously attempted to apply these conditions to our substrate as well. While she was ultimately able to form desired [2.2.2]bicycle 3.15, the reaction required significantly elevated temperatures (90 °C) and only proceeded in 29% yield over the two steps. We hypothesize that the C1-methoxy group leads to steric congestion about the vinyl group, preferentially orienting it away from the aromatic ring, and requiring higher temperatures in order for the desired cycloaddition to proceed.

Scheme 3-13. Birch/Diels–Alder reactions reported by Gin (top) and Jessica (bottom)

As I began to perform this chemistry, I found that the Birch reduction to afford 3.37 proceeded smoothly in my hands, although it was noted that the resultant unconjugated enone was unstable for extended periods of time (Scheme 3-14). Thus, this compound was not purified and the crude material was instead used directly in the subsequent Diels–Alder cycloaddition. Frustratingly, my initial attempts to reproduce this chemistry were met with complete failure; none of the desired Diels–Alder adduct was observed, with only an undetermined, apparently rearomatized compound seen by NMR and LCMS analysis. Efforts to vigorously exclude oxygen from the reaction conditions were explored to no avail. With that in mind, we proposed that we might only be achieving condensation of the pyrrolidine on the ketone in the reaction vessel, and upon opening the flask for work-up, oxygen in the air would then oxidize the diene to an aromatic system. With this hypothesis that it was not decomposition but simply incomplete reactivity in the reaction vessel that was the main issue, we adopted the use of a much smaller Schlenk flask which was submerged fully into the oil bath with a minimal headspace, in an effort to ensure the desired reaction temperatures could be achieved. Simultaneously, a second reaction was set-up in a sealed microwave vial and heated even higher using microwave irradiation, to 120 °C. To our delight, both of these trials led to formation of [2.2.2]bicycle 3.15. For operational simplicity, we elected to move forward with the microwave conditions, which allow for complete reactivity in only 2 hours, providing [2.2.2]bicycle 3.15 in a slightly improved 40% yield over 2 steps.

Scheme 3-14. Optimized Birch/Diels–Alder sequence to access [2.2.2]bicycle 3.15

3.4 Completing the Total Synthesis of Cossonidine With the heptacyclic core of the hetisine-type alkaloids constructed, we could finally begin addressing the unexplored chemistry to complete the total synthesis of cossonidine. This required deprotection and inversion of the C1 hydroxyl group to the axial position as well as conversion of the ketone group on the [2.2.2]bicycle to an allylic alcohol through methylenation and allylic oxygenation (Scheme 3-15). When examining the ideal order of operations for this sequence, we believed that ketone product 3.15 from the Diels–Alder reaction would be the most robust substrate for the likely harsh reaction conditions that would be required to cleave the aliphatic methyl ether at C1. Envisioning an oxidation-reduction sequence to be the simplest route to invert the C1 stereocenter, we first targeted Wittig methylenation product 3.38 to avoid chemoselectivity issues in the C1 ketone reduction. From exo-methylene compound 3.38, an oxidation-reduction sequence could then be explored to invert the C1 hydroxyl group to afford 3.39, followed by a selenium dioxide-mediated allylic oxygenation to complete the total synthesis of cossonidine (3.5).

Scheme 3-15. Conceptual plan to complete the total synthesis of cossonidine

While methyl ethers are often employed as alcohol protecting groups due to their robust stability to a wide range of reaction conditions, these strengths often turn into detriments when it comes time to cleave the ether and restore the free hydroxyl group. Aliphatic methyl ethers in particular are often very challenging to cleave, typically requiring the use of very harsh Lewis or Brønsted acids.30 We began by screening a number of conventional Lewis acids on methyl ether 31 32 3.15 (Table 3-2), including trimethylsilyl iodide (TMSI), boron tribromide (BBr3), methyl trimethylsilyl sulfide with zinc iodide,33 and dimethylboron bromide.34 We also briefly explored the use of the Brønsted acid HBr in an ionic liquid solvent, which has been shown to increase the 35 rate of SN2-type reactions. Unfortunately, none of these reagent systems led to the desired free alcohol 3.40, leading only to recovered starting material or nonspecific decomposition.

Table 3-2. Conditions explored for direct methyl ether cleavage

We next turned to conditions recently reported for O-demethylation by Wang and coworkers in their derivatization studies of diterpenoid alkaloid natural products.36 Treating alkaloids bearing multiple methyl ethers with a 6.5% solution of HBr in HOAc at 80 °C for 28 – 33 h, the authors reported isolating a mixture of acetates, bromides, and elimination products, depending on the position and relative reactivity of the methyl ethers. Given that our compound contained only a single methyl ether, we were hopeful that these conditions would be able to more cleanly provide us with a single product. Indeed, applying these conditions to 3.15 provided the corresponding C1-acetate 3.41 with retention of stereochemistry, although the reaction took around 5 days to reach full conversion. Gratifyingly, by heating the reaction mixture to 120 °C in the microwave reactor, we were able to reduce the reaction time from 5 days to only 1.5 h to provide acetate 3.41. This crude material could then be subjected to acetate cleavage using K2CO3 in MeOH, providing the equatorial free alcohol 3.40 in 57% yield over two steps (Scheme 3-16).

Scheme 3-16. Two-step deprotection of C1-hydroxyl group

Looking next to the methylenation reaction to introduce the exo-methylene, we explored the conditions utilized by Gin in their synthesis of nominine.5 While we were initially concerned about performing this reaction in the presence of the free hydroxyl group, treating 3.40 with 5.0 equivalents of preformed Wittig reagent and heating the reaction mixture to reflux for 12 h effectively converted the ketone carbonyl into exo-methylene 3.38 (Scheme 3-17). While we had also explored the use of a Julia olefination,37 a Tebbe methylenation,38 and alternative methods for forming the Wittig ylide, a Wittig reaction using the ylide formed with n- butyllithium proved to be the most effective. Frustratingly, one or more of the byproducts from this reaction appeared to co-elute with 3.38, rendering purification exceedingly challenging. Rather than struggle with sub-optimal purifications or risk losing significant amounts of material, we instead opted to investigate the subsequent oxidation conditions on the crude material.

We began by exploring the use of PDC as an oxidant,39 which provided our first successful oxidation to C1-ketone 3.42. However, this reaction was relatively messy and low- yielding, so alternate oxidants were investigated. Oxidation with the Dess–Martin periodinane22 provided none of the desired product, seemingly leading only to decomposition of the starting material. Applying a copper-catalyzed aerobic oxidation reported by the Stahl group,40 previously shown to work well on amine-bearing, sterically-congested alcohols, led to clean conversion to 3.42. Gratifyingly, this ketone no longer co-elutes with the Wittig reaction byproducts, and we can isolate 3.42 in 58% yield over 2 steps.

Scheme 3-17. Wittig methylenation and aerobic oxidation of the C1 hydroxyl group

The reduction of ketones on cyclohexane rings has been studied in great detail.41 As proposed by Felkin, the primary factor that distinguishes between an axial versus an equatorial approach of a nucleophile is the relative steric versus torsional strain involved in each transition state.42 Because the carbonyl oxygen is nearly but not entirely eclipsed by the equatorial C–H bonds, attack from the more accessible equatorial approach increases torsional strain by forcing the carbonyl group through a completely eclipsing interaction upon rehybridization. While attack along an axial approach would relieve this torsional strain, this approach is more sterically hindered due to the presence of the axial hydrogen atoms on the cyclohexane ring. As a result, small reducing agents like LiAlH4, NaBH4, and DIBAL preferentially attack from the axial side, minimizing torsional strain (Table 3-3). Bulky reducing agents like L-Selectride (LiBHsBu3) and lithium trisiamylborane (LiBH(siam)3), however, show a strong preference for attack from the equatorial direction to minimize steric interactions with the ring protons.43

Table 3-3. Stereoselectivity of Hydride Reducing Agents with 4-tert-butylcyclohexanone

Following this ample precedent, we began by investigating L-selectride, a bulky reductant known to favor reduction to provide the axial hydroxyl group (Table 3-4).43c Surprisingly, the only reduction product cleanly isolated from these reactions was equatorial alcohol 3.38. Investigating other reducing agents, DIBAL was found to be very slow to react, even in the presence of a Lewis acid,44 returning primarily starting material. A Meerwein– i Ponndorf–Verley reduction with Al(O Pr3) provided small amounts of the undesired equatorial

85 hydroxyl group along with significant amounts of recovered starting material. Using Superhydride (LiBHEt3), we observed a roughly 1:1 mixture of reduction products, providing some of the desired axial alcohol for the first time.45 While exciting, this result was curious as Superhydride is generally viewed as a more powerful but smaller reductant than L-selectride, contradicting the hypothesis of steric bulk being important for obtaining the desired selectivity. Building on this apparent trend, we next investigated the use of one of the smallest hydride reagents, LiAlH4. To our delight, this reduction proceeded with complete selectivity for the desired axial hydroxyl group (3.39), in direct contradiction to the common theoretical model for a simple cyclohexane ring. It is apparent that the steric environment around the C1 carbon atom is significantly altered by the presence of the [2.2.2]bicycle, leading bulky reagents to reduce the ketone from the undesired top face. Despite the clear trend that emerges from the data, it is not immediately clear why the much smaller LiAlH4 reverses this trend, as torsional effects would also be expected to drive LiAlH4 to attack along an axial approach as well. Nevertheless, through the 2-step sequence of Stahl oxidation followed by LiAlH4 reduction, we have been able to invert the C1 hydroxyl group, leaving only allylic oxygenation to complete the total synthesis.

Table 3-4. Reduction of the C1 carbonyl

Using the allylic oxygenation conditions reported by Gin in their nominine synthesis as a starting point,5 we began investigating the selenium dioxide-mediated allylic oxygenation of 3.39 (Scheme 3-18). While initial reactivity was rapid, over-oxidation to the corresponding enone was detected as a significant side reaction by LCMS. Through careful monitoring of reaction progress by TLC and LCMS, this reaction can be controlled to provide cossonidine (3.5) as the main product in 71% yield, completing the first total synthesis of this hetisine-type C20- diterpenoid alkaloid natural product.

Scheme 3-18. Allylic oxygenation to complete the total synthesis of cossonidine

3.5 Conclusion Building upon previous work conducted in the Sarpong group, we have successfully completed the first total synthesis of cossonidine (3.5). Key developments in this route include: 1) application of an aryne acyl-alkylation reaction in a complex setting to forge the central 6-7-6 tricycle, 2) use of a one-step oxidation of a primary alcohol to a nitrile to reduce the step count of the original synthesis by two and improve the yield of the transformation, 3) application of an underutilized protocol for chemoselective nitrile reductions using cobalt boride, 4) optimization of the Birch reduction/Diels–Alder cycloaddition sequence to afford the [2.2.2]bicycle, 5) application of new procedures for methyl ether cleavage and the aerobic oxidation of hindered hydroxyl groups, and 6) an examination of a series of reducing agents to selectively set the stereochemistry of the C1 hydroxyl group. The successful implementation of this route paves the way for further studies of other natural and unnatural derivatives, either through a divergent synthesis or utilizing the C1 and C15 hydroxyl groups as directing groups for further functionalization reactions. The synthesis of these derivatives and a thorough exploration of the chemical space around this core will be the subject of future studies, with the ultimate goal of exploring the potential bioactivities and ion channel interactions of these small molecules.

3.6 Experimental Procedures and Characterization Data

All reagents were obtained from commercial chemical suppliers and used without further purification unless otherwise noted. Unless stated otherwise, all reactions were performed in oven-dried glassware sealed with rubber septa under a nitrogen atmosphere and were stirred with Teflon-coated magnetic stir bars. Dry tetrahydrofuran (THF), benzene, toluene, acetonitrile (CH3CN), methanol (MeOH), and triethylamine (Et3N) were degassed with argon for 45 min and passed through activated alumina columns. Dichloromethane (CH2Cl2) was distilled over calcium hydride before use. Reactions were monitored by thin layer chromatography (TLC) on Silicycle SiliaplateTM glass backed TLC plates (250 μm thickness, 60 Å porosity, F-254 indicator) and visualized by UV irradiation and potassium permanganate (KMnO4), p- anisaldehyde, or Dragendorff-Munier stain. Volatile solvents were removed under reduced pressure with a rotary evaporator. Flash column chromatography was performed either manually using Silicycle 60 Å, 230x400 mesh silica gel (40-63 μm) or automated on a Yamazen Smart Flash W-Prep 2XY system with Yamazen Universal silica gel purification columns, loaded using a Yamazen silica gel inject column. 1H NMR and 13C NMR spectra were taken with Bruker spectrometers operating at 300, 400, 500, or 600 MHz for 1H (75, 100, 125, and 150, MHz for 13 C) in CDCl3. Chemical shifts are reported in parts per million (δ) relative to the residual solvent signal (1H NMR: δ = 7.26; 13C NMR: δ = 77.16). NMR data are reported as follows: chemical shift (multiplicity, coupling constants where applicable, number of hydrogens). Splitting is reported with the following symbols: s = singlet, bs = broad singlet, d = doublet, t = triplet, q = quartet, dd = doublet of doublets, ddd = doublet of doublet of doublets, dt = doublet of triplets, m = multiplet. IR spectra were taken on a Nicolet 380 spectrometer as thin films on NaCl plates or on a Bruker ALPHA FTIR spectrometer and are reported in frequency of absorption (cm-1). Only selected resonances are reported. High-resolution mass spectra (HRMS) were obtained by the mass spectral facility at the University of California, Berkeley using a Finnigan/Thermo LTQ/FT instrument for ESI and a Waters Autospec Premiere Instrument for EI. X-ray crystallographic analysis was performed by the X-ray crystallography facility at the

University of California, Berkeley on a MicroStar-H X8 APEX-II diffractometer with Cu-Kα radiation (λ = 1.54178 Å) and structures were visualized using CYLview.

Dienophile 3.11. To a solution of diphenyl diselenide (30.2 g, 97 mmol, 0.6 equiv) in CH2Cl2 was added bromine (5.0 mL, 97 mmol, 0.6 equiv) and the resultant solution was stirred at rt for 90 min. At this time, the reaction mixture was cooled to 0 °C, pyridine (19.6 mL, 242 mmol, 1.5 equiv) was added, and the solution was stirred at 0 °C for 10 min. Methyl 2- oxocyclopentanecarboxylate (3.16, 20 mL, 162 mmol, 1.0 equiv) was added dropwise and the resultant mixture was stirred at 0 °C for 2 h at which time the ice bath was removed and the mixture was extracted with 1M HCl (2 x 200 mL), sat. NaHCO3 (200 mL), and brine (200 mL). The organic layer was dried over Na2SO4, filtered, and concentrated. Column chromatography (9:1 then 7:3 hexanes/EtOAc) provided the α-selenide, which was dissolved in CH2Cl2 (450 mL) open to air and cooled to 0 °C. H2O2 (16.3 mL, 35% in H2O, 1.2 equiv) was slowly added into the vortex of the rapidly stirring reaction mixture. The solution was stirred vigorously and the ice bath was allowed to slowly expire over the course of 1 h, at which time a further 15 mL of H2O2 was added. After 20 min, H2O (200 mL) was added and the mixture was extracted. The organic layer was washed with sat. NaHCO3 (2 x 200 mL) and bring (200 mL), then dried over Na2SO4, filtered, and concentrated to provide dienophile 3.11 as a yellow liquid (20.8 g, ~quant.). Due to the instability of dienophile 3.11, this compound was used immediately in the 1 next step. H NMR (300 MHz, CDCl3) δ 8.42 (t, J = 2.7 Hz, 1H), 3.82 (s, 3H), 2.74 (dt, J = 4.6, 2.8 Hz, 2H), 2.55 (t, J = 4.8 Hz, 2H), in agreement with previously reported spectral data.12,46

Diels–Alder Adduct 3.12. To a 500 mL Schlenk flask was added dienophile 3.11 (17.6 g, 126 mmol, 1.0 equiv), diene 3.10 (54.0 g, 236 mmol, 1.9 equiv) and toluene (250 mL). The resulting mixture was evacuated and backfilled with nitrogen, the Schlenk flask was sealed, and the solution was stirred at 100 °C for 10 h. At this time, the reaction mixture was allowed to cool to rt and concentrated. Column chromatography (98:2 then 95:5 hexanes/EtOAc) provided Diels– 1 Alder adduct 3.12 as a yellow oil (29.6 g, 71%). H NMR (300 MHz, CDCl3) δ 5.99 (ddd, J = 10.4, 4.3, 2.7 Hz, 1H), 5.71 (dt, J = 10.4, 0.9 Hz, 1H), 4.35 (m, 1H), 3.73 (s, 3H), 3.63 (dd, J = 8.1, 4.4 Hz, 2H), 3.31 (s, 3H), 2.99 (dt, J = 12.3, 6.9 Hz, 1H), 2.52 – 2.43 (m, 1H), 2.41 – 2.34 (m, 1H), 2.30 – 2.17 (m, 1H), 2.02 – 1.83 (m, 2H), 0.90 (s, 9H), 0.06 (s, 6H), in agreement with previously reported spectral data.47

Hydrindanone 3.17. Diels–Alder adduct 3.12 (6.45 g, 17.5 mmol) was taken up in EtOAc (250 mL) in a flame-dried round-bottom flask with a stirbar, to which was added Pd/C (650 mg, 10% by mass). The reaction flask was evacuated and backfilled with H2 three times before being left to stir under a H2 atmosphere. When the reaction was complete by NMR analysis (~24 h), the suspension was filtered through Celite, eluted with EtOAc, and concentrated to give the reduced 1 product 3.17 (6.36 g, 17.2 mmol, 98%). H NMR (600 MHz, CDCl3): δ 4.08 (s, 1H), 3.69 (s, 3H), 3.53 (dt, J = 24, 10 Hz, 2H), 3.17 (s, 3H), 3.02 (q, J = 6.6 Hz, 1H), 2.39 (dd, J = 19, 8.4 Hz, 1H), 2.25 (q, J = 9.0 Hz, 1H), 2.08 – 2.00 (m, 2H), 1.82 – 1.75 (m, 2H), 1.44 – 1.38 (m, 3H), 0.89 (s, 9H), 0.05 (s, 6H), in agreement with previously reported spectral data.47

Diol 3.18. To a cooled (0 °C) solution of hydrindanone 3.17 (7.04 g, 19.0 mmol) in dry Et2O (200 mL) was added LiAlH4 (2.89 g, 76.2 mmol, 4 equiv) with vigorous stirring and the ice bath was then allowed to slowly expire. After the reaction was complete as judged by TLC analysis (~3 h), the mixture was cooled to 0 °C and quenched by the sequential addition of H2O (2.9 mL), 10% NaOH (2.9 mL), and H2O (8.7 mL). The resulting mixture was stirred vigorously at rt until the solids turned white. The mixture was then filtered and the solid residue washed with Et2O. The filtrate was dried over Na2SO4, filtered, and concentrated to provide diol 3.18 as a white solid (6.06 g, 17.6 mmol, 92%) which was advanced without further purification. Rf: 0.19 (2:1 1 hexanes/EtOAc, p-anisaldehyde stain). mp: 67 – 68 °C. H NMR (400 MHz, CDCl3) δ 4.15 (td, J = 10.8, 6.7 Hz, 1H), 3.81 (t, J = 3.0 Hz, 1H), 3.72 (t, J = 9.1 Hz, 1H), 3.44 – 3.37 (m, 3H), 3.31 (s, 3H), 2.77 (d, J = 11.4 Hz, 1H), 2.40 (d, J = 7.7 Hz, 1H), 2.20 – 2.05 (m, 2H), 1.86 – 1.62 (m, 13 3H), 1.59 – 1.32 (m, 5H), 0.88 (s, 9H), 0.02 (s, 6H). C NMR (100 MHz, CDCl3) δ 81.8, 76.8, 68.9, 66.3, 55.4, 50.6, 39.9, 37.9, 34.0, 25.8, 23.0, 22.0, 18.2, 17.6, -5.47, -5.50. IR (thin film) -1 ṽmax cm 3418 (broad), 2929, 2891, 2855, 1471, 1255, 1085, 836, 775. HRMS (ESI) calcd for + + [C18H37O4Si] ([M+H] ): m/z 345.2456, found 345.2454.

Ketoaldehyde 3.19. To a flame-dried 500 mL round-bottomed flask equipped with a stir bar was added diol 3.18 (6.06 g, 17.6 mmol) in dry CH2Cl2 (300 mL) followed by N-methylmorpholine oxide (7.31 g, 62.4 mmol, 3.5 equiv) and 4Å molecular sieves (8.94 g, 0.5 g/mmol). The resulting mixture was stirred at rt for 15 min. TPAP (310 mg, 0.05 equiv) was then added in a single portion and the mixture was stirred for 2 h. The reaction mixture was then filtered through a plug of Celite then a plug of SiO2 and eluted with EtOAc. The resulting solution was concentrated to give ketoaldehyde 3.19 as a yellow oil (5.77 g, 16.9 mmol, 96%) which was 1 advanced without further purification. Rf: 0.61 (2:1 hexanes/EtOAc, p-anisaldehyde stain). H NMR (400 MHz, CDCl3) δ 9.45 (s, 1H), 4.02 (t, J = 2.7 Hz, 1H), 3.60 – 3.51 (m, 2H), 3.21 (s, 3H), 2.86 (dt, J = 12.4, 6.1 Hz, 1H), 2.45 – 2.38 (m, 1H), 2.22 – 2.13 (m, 1H), 2.06 – 2.00 (m, 1H), 1.90 – 1.79 (m, 2H), 1.47 – 1.32 (m, 2H), 1.27 – 1.24 (m, 1H), 1.21 – 1.12 (m, 1H), 0.90 (s, 13 9H), 0.06 (s, 6H). C NMR (100 MHz, CDCl3) δ 214.5, 198.4, 77.0, 68.5, 65.3, 57.1, 39.4, 38.1, -1 38.0, 25.8, 25.1, 20.2, 18.2, 16.8, -5.4, -5.5. IR (thin film) ṽmax cm 2930 (broad), 2712, 1751, + + 1716, 1463, 1093, 838, 776. HRMS (ESI) calcd for [C18H32O4SiNa] ([M+Na] ): m/z 363.1962, found 363.1964.

Vinyl Ketone 3.20. To ketoaldehyde 3.19 (3.50 g, 10.3 mmol) in dry THF (120 mL) in a 250 mL round-bottomed flask was added sequentially PPh3 (4.15 g, 15.8 mmol, 1.5 equiv), dry isopropanol (1.20 mL, 15.5 mmol, 1.5 equiv), trimethylsilyldiazomethane (10.3 mL, 20.6 mmol, 2.0 M in Et2O, 2 equiv), and RhCl(PPh3)3 (0.515 g, 0.54 mmol, 0.05 equiv). The reaction mixture was stirred at rt until the reaction was judged complete by TLC analysis (~6 h). The mixture was then quenched by the addition of 10% aq. H2O2 (10 mL) and extracted once with

CH2Cl2 (50 mL). The combined organic layers were washed with water, then brine, and concentrated to give a white-orange solid, which was taken up in diethyl ether and filtered. Column chromatography (30:1 hexanes/EtOAc) provided vinyl ketone 3.20 as a white solid 1 (3.49 g, 81%). Rf: 0.49 (9:1 hexanes/EtOAc, p-anisaldehyde stain). mp: 34.6 – 35.1 °C. H NMR (500 MHz, CDCl3) δ 5.81 (dd, J = 17.6, 11.0 Hz, 1H), 5.22 – 5.13 (m, 2H), 3.54 (ddd, J = 25.9, 9.6, 7.0 Hz, 2H), 3.47 (s, 1H), 3.15 (s, 3H), 2.51 (dt, J = 12.2, 6.1 Hz, 1H), 2.38 – 2.28 (m, 1H), 2.11 – 1.99 (m, 2H), 1.96 – 1.93 (m, 1H), 1.90 – 1.87 (m, 1H), 1.73 (dt, J = 10.5, 7.0 Hz, 1H), 1.47 – 1.39 (m, 1H), 1.36 (d, J = 13.3 Hz, 2H), 0.89 (s, 9H), 0.05 (s, 6H). 13C NMR (125 MHz, CDCl3) δ 220.3, 138.4, 115.8, 82.0, 65.8, 57.5, 57.0, 40.4, 38.7, 37.7, 25.9, 23.7, 20.1, -1 18.3, 17.5, -5.35, -5.44. IR (thin film) ṽmax cm 2953, 2930, 2893, 2857, 1743, 1636, 1093, 838. + + HRMS (ESI) calcd for [C19H35O3Si] ([M+H] ): m/z 339.2350, found 339.2355.

β-Ketoester 3.9. Vinyl ketone 3.20 (3.42 g, 10.1 mmol) was dissolved in THF (80 mL) in an oven-dried 250 mL round-bottomed flask with a stir bar. The solution was cooled to –78 °C and LiHMDS (20.2 mL, 1 M in THF, 2.0 equiv) was added slowly over 20 min. The reaction mixture was stirred at –78 °C for 30 min, at which time allyl cyanoformate2 (2.79 g, 25.3 mmol, 2.5 equiv) was added. The reaction mixture was warmed to 0 °C and stirred at that temperature for 1 h. The reaction mixture was quenched by the addition of sat. NH4Cl(aq) (50 mL) and the aqueous layer was extracted with EtOAc (3 x 100 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated. Automated column chromatography (0 → 10% EtOAc in hexanes gradient) provided β-ketoester 3.9 as a colorless oil (3.75 g, 88%, 1:1 dr). Rf: 0.37 1 (9:1 hexanes/EtOAc, UV, p-anisaldehyde stain). H NMR (500 MHz, CDCl3) δ 5.98 – 5.76 (m, 4H), 5.40 – 5.36 (m, 1 H), 5.31 – 5.27 (m, 1H), 5.24 – 5.18 (m, 6H), 4.73 – 4.62 (m, 2H), 4.58 – 4.56 (m, 2H), 3.61 – 3.49 (m, 6H), 3.36 (d, J = 9.0 Hz, 1H), 3.17 – 3.13 (m, 4H), 3.08 (s, 3H), 2.84 (dt, J = 12.9, 6.5 Hz, 1H), 2.60 – 2.46 (m, 2H), 2.33 – 2.26 (m, 1H), 2.06 – 1.87 (m, 6H), 1.52 – 1.44 (m, 1H), 1.41 – 1.35 (m, 5H), 0.90 (s, 9H), 0.89 (s, 9H), 0.06 (s, 12H). 13C NMR (100 MHz, CDCl3) δ 213.0, 211.1, 169.4, 167.6, 137.6, 137.5, 132.1, 131.7, 118.2, 117.1, 116.6, 116.4, 82.4, 81.6, 65.7, 65.6, 65.50, 65.46, 58.2, 57.5, 57.0, 56.8, 54.8, 54.7, 39.2, 37.51, 37.45, -1 25.9, 25.0, 23.9, 23.7, 23.6, 18.22, 18.20, 17.4, 17.0, -5.37, -5.43, -5.45. IR (thin film) ṽmax cm + 3086, 2891, 2859, 2739, 1755, 1736, 1649, 1638. HRMS (ESI) calcd for [C23H39O5Si] ([M+H]+): m/z 423.2561, found 423.2558.

4-Methoxyphenyl isopropylcarbamate (3.22). To a 500 mL round-bottomed flask was added 4-methoxyphenol (3.21, 10.0 g, 80.6 mmol) and CH2Cl2 (160 mL), followed by isopropylisocyanate (11.9 mL, 120.8 mmol, 1.5 equiv) and triethylamine (2.2 mL, 16.1 mmol, 0.2 equiv). The clear reaction mixture was allowed to stir at rt for 20 h, at which time the reaction mixture was concentrated to provide carbamate 3.22 as a white solid (16.9 g, 99%), which was advanced without further purification. Rf: 0.56 (CH2Cl2, UV, p-anisaldehyde stain). 1 mp: 114 – 116 °C. H NMR (400 MHz, CDCl3) δ 7.03 (d, J = 8.6 Hz, 2H), 6.85 (d, J = 8.7 Hz, 2H), 5.15 (d, J = 7.8 Hz, 1H), 3.85 (m, 1H), 3.75 (s, 3H), 1.16 (d, J = 6.7 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ 156.6, 154.0, 144.4, 122.3, 114.0, 55.3, 43.1, 22.6. IR (NaCl, thin film) νmax 3289, 2966, 1691, 1556, 1507, 1458, 1241, 1209, 1172, 1037. HRMS (ESI) calcd for + + [C11H16NO3] ([M+H] ): m/z 210.1125, found 210.1126.

4-Methoxy-2-(trimethylsilyl)phenyl isopropylcarbamate (3.23). Carbamate 3.22 (17.0 g, 81.2 mmol) was taken up in Et2O (680 mL) and THF (115mL) and cooled to 0 °C. TMEDA (17.0 mL, 114 mmol, 1.4 equiv) was added, followed by slow addition of TBSOTf (22.4 mL, 97.4 mmol, 1.2 equiv). The reaction mixture was stirred at 0 °C for 5 min, then at rt for 30 min. A second portion of TMEDA (42.6 mL, 284.2 mmol, 3.5 equiv) was added and the reaction mixture was cooled to –78 °C. n-BuLi (113 mL, 2.5M in hexanes, 284 mmol, 3.5 equiv) was added over 1 h by syringe pump, after which the mixture was stirred at that temperature for 3 h. TMSCl (72.1 mL, 568 mmol, 7 equiv) was added over 1 h by syringe pump and the mixture was stirred for an additional 1 h. The reaction mixture was then quenched by the addition of 1N NaHSO4 (350 mL), warmed to rt, and stirred for 30 min. The aqueous layer was extracted once with Et2O (500 mL) and the combined organic layers were dried over MgSO4, filtered, and concentrated. Column chromatography with CH2Cl2 gave 3.23 as a white solid (24.3 g, quant.). 1 Rf: 0.35 (CH2Cl2, UV, p-anisaldehyde stain). mp: 86 – 88 °C. H NMR (400 MHz, CDCl3) δ 7.02 (d, J = 8.8 Hz, 1H), 6.95 (d, J = 2.8 Hz, 1H), 6.88 (dd, J = 8.8, 3.2 Hz, 1H), 4.76 (bd, J = 7.9 Hz, 1H), 3.92 (m, 1H), 3.80 (s, 3H), 1.23 (d, J = 6.8 Hz, 6H), 0.27 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 156.4, 154.2, 149.1, 133.0, 123.1, 120.0, 114.8, 55.5, 43.4, 23.0, -1.0. IR (thin -1 film) ṽmax cm 3363, 3003, 2974, 2934, 1704, 1569, 1531, 1474, 1405, 1270. HRMS (ESI) calcd + + for [C14H23NO3NaSi] ([M+Na] ): m/z 304.1339, found 304.1338.

2-Bromo-4-methoxy-6-(trimethylsilyl)phenyl isopropylcarbamate (3.24). Silyl carbamate 3.23 (24.3 g, 86.5 mmol) was dissolved in Et2O (860 mL) and cooled to 0 °C. TMEDA (14.3 mL, 95.2 mmol, 1.1 equiv) was added, followed by slow addition of TBSOTf (20.9 mL, 90.8 mmol, 1.05 equiv). The reaction mixture was stirred at 0 °C for 5 min, then at rt for 30 min. A second portion of TMEDA (28.5 mL, 190 mmol, 2.2 equiv) was added and the reaction mixture was cooled to –78 °C. s-BuLi (158 mL, 1.2 M in cyclohexane, 190 mmol, 2.2 equiv) was added over 1 h by syringe pump, after which the mixture was stirred at that temperature for 1 h. Dibromoethane (18.6 mL, 216 mmol, 2.5 equiv) was then added over 5 min and the mixture was stirred for 1 h. The reaction mixture was then quenched by the addition of MeOH (8.6 mL) and 1 M HCl (525 mL), warmed to rt, and stirred for 45 min. The aqueous layer was extracted once with Et2O (500 mL) and the combined organic layers were dried over MgSO4, filtered, and concentrated. Column chromatography with CH2Cl2 then 10% EtOAc in CH2Cl2 provided bromosilyl carbamate 3.24 as a white solid (31.6 g, quant.). Rf: 0.55 (CH2Cl2, UV, p- 1 anisaldehyde stain). mp: 86 – 98 °C. H NMR (400 MHz, CDCl3) δ 7.10 (d, J = 3.0 Hz, 1H), 6.91 (d, J = 3.0 Hz, 1H), 5.06 (bs, 1H), 3.90 (m, 1H), 3.77 (s, 3H), 1.22 (d, J = 6.4 Hz, 6H), 0.29 13 (s, 9H) C NMR (100 MHz, CDCl3) δ 156.9, 152.7, 145.8, 135.8, 119.7, 118.5, 117.9, 55.6,

-1 43.4, 22.8, -1.0. IR (thin film) ṽmax cm 3342, 2966, 1744, 1720, 1589, 1573, 1454, 1421, 1250, + + 1201. HRMS (ESI) calcd for [C14H22NO3BrNaSi] ([M+Na] ): m/z 382.0445, found 382.0446.

2-Bromo-4-methoxy-6-(trimethylsilyl)phenyl trifluoromethanesulfonate (3.8). To a solution of Et2NH (10.7 mL, 104 mmol, 1.2 equiv) in THF (130 mL) in a 500 mL round-bottomed flask at –78 °C was slowly added n-BuLi (42.0 mL, 2.5 M in hexanes, 104 mmol, 1.2 equiv). After 15 min, a solution of bromosilyl carbamate 3.24 (31.6 g, 87 mmol) in THF (130 mL) was added slowly. The reaction mixture was stirred at –78 °C for 20 min, then at rt for 25 min, at which time it was quenched with sat. NH4Cl(aq) (50 mL) and extracted with Et2O (3 x 100 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated. Column chromatography with 3% EtOAc in hexanes provided known phenol 3.2548 (20.0 g, 72.7 mmol). Phenol 3.25 was then taken up in CH2Cl2 (300 mL) and cooled to 0 °C. Pyridine (9.50 mL, 118 mmol, 1.6 equiv) was added, followed by slow addition of Tf2O (15.0 mL, 89.2 mmol, 1.2 equiv). The reaction mixture was allowed to warm to rt and stirred until judged complete by NMR analysis (~20 h). The mixture was then poured into sat. NaHCO3(aq) (200 mL), the layers were separated, and the aqueous layer was extracted with CH2Cl2 (3 x 200 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated to give a dark red oil. Column chromatography (9:1 hexanes/EtOAc then 4:1 hexanes/EtOAc) provided o-silyl triflate 3.8 as a 1 pale yellow oil (29.6 g, 84% over 2 steps). Rf: 0.51 (9:1 hexanes/EtOAc, UV). H NMR (500 13 MHz, CDCl3) δ 7.15 (d, J = 3.1 Hz, 1H), 6.98 (d, J = 3.0 Hz, 1H), 3.82 (s, 3H), 0.39 (s, 9H). C NMR (150 MHz, CDCl3) δ 158.6, 142.2, 138.2, 121.3, 119.8, 118.6 (q, J = 320.7 Hz), 116.9, -1 55.8, -0.1. IR (thin film) ṽmax cm 3078, 3008, 2959, 2905, 2842, 1580, 1560, 1406, 1213, 845. 79 + + HRMS (EI) calcd for [C11H14O4F3SiS Br] ([M] ): m/z 405.9518, found 405.9518.

Tricycle 3.13. To a flame-dried 20 mL microwave vial (or Schlenk flask) equipped with a stir bar was added CsF (449 mg, 2.96 mmol, 2.5 equiv) in a glovebox. The microwave vial was sealed, removed from the glovebox, and dried by heating to 100 °C under vacuum for 1 h. At that time, the vial was removed from the heat, placed under N2, and the temperature of the oil bath was lowered to 90 °C. A solution of β-ketoester 3.9 (500 mg, 1.18 mmol) in CH3CN (3 mL) in a flame-dried flask under N2 was added to the vial, followed by a solution of o-silyl triflate 3.8 (959 mg, 2.37 mmol, 2 equiv) in CH3CN (3 mL) in a flame-dried flask under N2. The reaction mixture was returned to the oil bath and stirred at 90 °C for 2 h. At that time, the vial was removed from the oil bath and the reaction mixture allowed to cool to rt before brine (18

93 mL) was added to quench the reaction mixture. The reaction mixture was extracted with EtOAc (3 x 25 mL), dried over MgSO4, filtered, and concentrated. Automated column chromatography (0% → 16% EtOAc in hexanes gradient) provided tricycle 3.13 as a white foam (292 mg, 41%). 1 Rf: 0.60 (4:1 hexanes/EtOAc, UV, p-anisaldehyde stain). mp: 128 – 130 °C. H NMR (300 MHz, CDCl3) δ 6.95 (d, J = 2.4 Hz, 1H), 6.60 (d, J = 2.1 Hz, 1H), 5.88 (ddt, J = 17.1, 10.5, 5.7 Hz, 1H), 5.38 (d, J = 4.2 Hz, 1H), 5.35 (d, J = 2.1 Hz, 1H), 5.27 (dd, J = 17.1, 1.5 Hz, 1H), 5.20 (dd, J = 10.5, 1.2 Hz, 1H), 5.13 – 5.04 (m, 1H), 4.70 – 4.56 (m, 2H), 4.24 – 4.19 (m, 2H), 3.75 (s, 3H), 3.40 (d, J = 7.5 Hz, 2H), 3.36 (s, 3H), 2.22 – 2.11 (m, 2H), 2.02 – 1.87 (m, 3H), 1.53 – 1.33 (m, 2H), 1.29 – 1.18 (m, 1H), 0.76 (s, 9H), 0.00 (s, 3H), -0.04 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 202.2, 172.8, 160.8, 138.6, 136.6, 131.8, 130.6, 120.0, 119.7, 118.4, 116.7, 110.1, 80.3, 65.3, 64.4, 61.0, 57.7, 55.4, 45.9, 37.6, 34.6, 27.6, 25.7, 23.4, 18.2, 18.0, -5.5, -5.6. IR (thin film) -1 + ṽmax cm 2930, 2856, 1738, 1697, 1599, 1090, 836, 776. HRMS (ESI) calcd for [C30H44BrO6Si] ([M+H]+): m/z 607.2085, found 607.2090.

Carboxylic Acid 3.28. Tricycle 3.13 (1.20 g, 1.97 mmol) was dissolved in CH2Cl2 (20 mL) in a 50 mL round-bottomed flask with a stir bar. The flask was covered with aluminum foil, then Pd(PPh3)4 (46 mg, 0.039 mmol, 0.02 equiv) was added in a single portion, followed by phenylsilane (0.51 mL, 4.14 mmol, 2.1 equiv). The reaction mixture was stirred at rt for 6 h. The crude reaction mixture was then concentrated and purified by automated column chromatography (9:1 then 1:2 hexanes/EtOAc) to provide carboxylic acid 3.28 as a white solid (1.04 g, 93%). Rf: 0.54 (2:1 hexanes/EtOAc, UV, p-anisaldehyde stain). mp: 73 – 75 °C 1 (decomposition). H NMR (400 MHz, CDCl3) δ 10.28 (s, 1H), 6.97 (s, 1H), 6.75 (s, 1H), 5.38 (dd, J = 9.0, 3,1 Hz, 2H), 5.13 – 5.06 (m, 1H), 4.28 – 4.21 (m, 2H), 3.78 (s, 3H), 3.41 – 3.37 (m, 5H), 2.26 – 2.14 (m, 2H), 2.03 – 2.00 (m, 1H), 1.93 – 1.84 (m, 2H), 1.51 – 1.36 (m, 2H), 1.26 – 13 1.18 (m, 1H), 0.76 (s, 9H), -0.01 (s, 3H), -0.03 (s, 3H). C NMR (100 MHz, CDCl3) δ 202.5, 178.8, 161.0, 138.1, 136.7, 130.8, 120.3, 120.0, 116.6, 110.9, 80.4, 64.5, 61.2, 57.8, 55.7, 46.1, -1 37.7, 34.7, 27.8, 25.9, 23.5, 18.4, 18.2, -5.3, -5.5. IR (thin film) ṽmax cm 2927, 1699, 1597, + + 1464, 1250, 1085. HRMS (ESI) calcd for [C27H39O6BrNaSi] ([M+Na] ): m/z 589.1592 found 589.1589.

Tricyclic Alkene 3.29. To a flame-dried 10 mL Pyrex reaction tube with stir bar was added carboxylic acid 3.28 (232 mg, 0.409 mmol) as a solution in 1,2-DCE (4.1 mL), followed by DIH

(311 mg, 0.818 mmol, 2 equiv). The reaction tube was sealed and sparged with Ar for 30 min, at which time the reaction tube was placed in front of a 600W tungsten-filament lamp at a distance of 0.2 m such that the reaction mixture was also heated by the lamp to reflux. After 1 h, the light was turned off and the reaction mixture was allowed to cool to rt before being quenched by the addition of 1M NaHSO3 (5 mL). The mixture was extracted with CH2Cl2 (3 x 5 mL) and the combined organic layers were washed with brine, dried over MgSO4, filtered, and concentrated. Automated column chromatography (0% → 22% EtOAc in hexanes gradient) provided tricyclic alkene 3.29 as a yellow oil (157 mg, 74%). Rf: 0.69 (2:1 hexanes/EtOAc, UV, p-anisaldehyde 1 stain). H NMR (400 MHz, CDCl3) δ 6.99 (d, J = 2.8 Hz, 1H), 6.51 (d, J = 2.4 Hz, 1H), 6.26 (dd, J = 10.6, 1.8 Hz, 1H), 6.13 (dd, J = 10.7, 6.2 Hz, 1H), 5.54 – 5.41 (m, 2H), 5.31 (dd, J = 15.6, 2.5 Hz, 1H), 4.04 – 3.99 (m, 1H), 3.78 (s, 3H), 3.52 – 3.43 (m, 2H), 3.30 (s, 3H), 3.29 – 3.23 (m, 1H), 2.08 – 1.96 (m, 1H), 1.94 – 1.87 (m, 1H), 1.56 – 1.36 (m, 3H), 0.80 (s, 9H), -0.01 13 (s, 3H), -0.03 (s, 3H). C NMR (100 MHz, CDCl3) δ 200.5, 160.2, 139.2, 135.2, 134.0, 132.4, 125.5, 122.1, 120.5, 117.8, 112.1, 80.0, 71.5, 65.3, 57.6, 55.5, 36.7, 36.6, 25.8, 23.7, 18.7, 18.2, - -1 5.4, -5.5. IR (thin film) ṽmax cm 3084, 3038, 2925, 1703, 1692, 1628, 1588, 1092. HRMS (ESI) + + calcd for [C26H38O4BrSi] ([M+H] ): m/z 521.1717, found 521.1724.

Primary Alcohol 3.14. To a solution of tricyclic alkene 3.29 (1.01 g, 1.94 mmol) in THF (19.4 mL) at 0 °C in a 100 mL round-bottomed flask was added TBAF (4.1 mL, 1.0 M in THF, 2.1 equiv). The reaction mixture was allowed to warm to rt and stirred for 16 h at this temperature, at which time the mixture was diluted with EtOAc (25 mL) and washed sequentially with 1 N HCl (10 mL) and brine (10 mL). The organic layer was dried over MgSO4, filtered, and concentrated, then purified through a plug of silica with 3:2 hexanes/EtOAc to provide primary alcohol 3.14 as a white solid (690 mg, 87%). Rf: 0.21 (2:1 hexanes/EtOAc, UV, p- anisaldehyde 1 stain). mp: 146 – 148 °C. H NMR (600 MHz, CDCl3) δ 6.98 (d, J = 2.4 Hz, 1H), 6.52 (d, J = 2.4, 1H), 6.27 (dd, J = 10.7, 1.9 Hz, 1H), 6.10 (dd, J = 10.7, 6.2 Hz, 1H), 5.51 – 5.41 (m, 2H), 5.31 (d, J = 16.8, 1H), 4.00 (s, 1H), 3.76 (s, 3H), 3.52 – 3.47 (m, 2H), 3.29 – 3.24 (m, 4H), 2.01 – 1.95 (m, 1H), 1.90 (dd, J = 13.8, 3.0 Hz, 1H), 1.74 (s, 1H), 1.56 – 1.44 (m, 2H), 1.38 (dd, J = 13 12.6, 3.0 Hz, 1H). C NMR (150 MHz, CDCl3) δ 200.4, 160.4, 139.0, 134.8, 134.0, 132.6, 126.0, 122.3, 120.7, 118.1, 112.3, 79.9, 71.5, 65.3, 57.7, 55.6, 36.9, 36.9, 23.7, 18.8. IR (thin -1 film) ṽmax cm 3509, 3472, 2941, 1678, 1588, 1465, 1251, 1089. HRMS (ESI) calcd for + + [C20H23O4BrNa] ([M+Na] ): m/z 429.0672, found 429.0667.

Nitrile 3.31. Primary alcohol 3.14 (690 mg, 1.69 mmol) was dissolved in CH3CN (30.5 mL) and H2O (3.4 mL) in a 100 mL round-bottomed flask and cooled to 0 °C. To this solution was 95 sequentially added TEMPO (40 mg, 0.254 mmol, 0.15 equiv), NH4OAc (783 mg, 10.2 mmol, 6.0 equiv), then PIDA (1.64 g, 5.08 mmol, 3.0 equiv) portion-wise. The mixture was allowed to slowly warm to rt and stirred for 2 h, at which time brine (20 mL) was added and the reaction mixture was extracted with EtOAc (3 x 25 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated. Column chromatography (15% then 20% EtOAc in hexanes) provided nitrile 3.31 as a white solid (656 mg, 96%). Rf: 0.43 (2:1 hexanes/EtOAc, UV, p- 1 anisaldehyde stain) mp: 205 – 207 °C. H NMR (500 MHz, CDCl3) δ 7.03 (d, J = 2.4 Hz, 1H), 6.59 (d, J = 2.4 Hz, 1H), 6.42 (dd, J = 10.7, 2.0 Hz, 1H), 6.25 (dd, J = 10.6, 6.0 Hz, 1H), 5.52 (d, J = 10.5 Hz, 1H), 5.47 – 5.42 (m, 1H), 5.35 (d, J = 17.3 Hz, 1H), 4.02 (m, 1H), 3.81 (s, 3H), 3.50 (m, 1H), 3.31 (s, 3H), 2.98 (dt, J = 13.1, 4.0 Hz, 1H), 2.16 (qd, J = 13.4, 3.7 Hz, 1H), 1.97 (dq, J = 14.4, 3.4 Hz, 1H), 1.81 (dd, J = 13.8, 3.6 Hz, 1H), 1.47 (tdd, J = 13.9, 4.1, 2.0 Hz, 1H). 13C NMR (150 MHz, CDCl3) δ 198.3, 160.7, 138.4, 133.10, 133.05, 131.6, 127.1, 122.6, 121.3, -1 120.9, 118.6, 112.4, 78.0, 70.1, 57.9, 55.6, 36.9, 27.0, 22.9, 19.9. IR (thin film) ṽmax cm 2931, + + 2239, 1695, 1590, 1544, 1459. HRMS (ESI) calcd for [C20H21O3NBr] ([M+H] ): m/z 402.0699, found 402.0705.

Methylated Nitrile 3.7. Nitrile 3.31 (327 mg, 0.813 mmol) was dried by azeotropic distillation with benzene (2 x 10 mL) and placed under N2 in a 50 mL round-bottomed flask. THF (16 mL) was added followed by LiHMDS (2.44 mL, 1.0 M in THF, 3.0 equiv) and the reaction mixture was stirred for 1 h at rt. At that time, iodomethane (1.00 mL, 16.3 mmol, 20 equiv) was added and the solution was stirred at rt for an additional 4 h. The reaction mixture was then quenched with sat. NH4Cl(aq) (10 mL) and extracted with EtOAc (3 x 20 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated. Automated column chromatography (12% → 33% EtOAc in hexanes gradient) provided methylated nitrile 3.7 as a white foam (197 1 mg, 58%). Rf: 0.21 (4:1 hexanes/EtOAc, UV, p-anisaldehyde stain). H NMR (400 MHz, CDCl3) δ 7.03 (d, J = 2.4 Hz, 1H), 6.59 (d, J = 2.4 Hz, 1H), 6.35 (d, J = 10.1 Hz, 1H), 6.25 (dd, J = 11.0, 6.4 Hz, 1H), 5.69 (dd, J = 17.8, 11.0 Hz, 1H), 5.43 (d, J = 10.8 Hz, 1H), 5.30 (d, J = 17.8 Hz, 1H), 4.16 (d, J = 3.7 Hz, 1H), 3.81 (s, 3H), 3.35 (s, 3H), 3.18 (d, J = 5.9 Hz, 1H), 2.42 (t, J = 13.9 Hz, 1H), 1.92 (d, J = 14.6 Hz, 1H), 1.72 – 1.61 (m, 2H), 1.52 (s, 3H). 13C NMR (150 MHz, CDCl3) δ 197.6, 160.9, 138.6, 136.4, 135.2, 132.4, 125.8, 124.9, 121.7, 120.5, 118.7, 112.3, 76.3, -1 70.2, 57.9, 55.8, 44.4, 36.6, 26.0, 25.7, 18.8. IR (thin film) ṽmax cm 3056, 2932, 2833, 2232, + + 1710, 1692, 1587. HRMS (ESI) calcd for [C21H23O3NBr] ([M+H] ): m/z 416.0856, found 416.0856.

Tertiary Amine 3.6. Methylated nitrile 3.7 (159 mg, 0.382 mmol) was dissolved in MeOH (19 mL) in a 20 mL microwave vial with a 2 x 5 mm stir bar. To this solution was added cobalt boride (160 mg, 100 wt%; pre-formed by adding sodium borohydride (1.9 g, 50.1 mmol, 5.0 equiv) to a solution of anhydrous cobalt (II) chloride (1.3 g, 10.0 mmol) in MeOH (100 mL) at 0 °C. After stirring at 0 °C for 15 minutes, the cobalt boride was isolated by filtration and used directly). This was followed by the addition of borane tert-butylamine complex (166 mg, 1.91 mmol, 5.0 equiv). The reaction mixture was then placed under N2 and heated to reflux in an oil bath for 6 h. A further 80 mg of cobalt boride and 80 mg of borane tert-butylamine complex was added and the vial was resealed, placed under N2, and heated to reflux for 18 h. At this time, the reaction flask was removed from the oil bath and allowed to cool to rt. The reaction mixture was then filtered through Celite with EtOAc. To this cloudy filtrate was added 8 mL of 3N HCl, and the resulting clear solution was brought to pH > 9 with 16 mL of 2N NaOH. The solution was extracted with EtOAc (3 x 50 mL) and the combined organic layers were washed with brine (50 mL) then dried over Na2SO4, filtered, and concentrated to provide 133 mg (0.316 mmol) of primary amine 3.33, which was used in the next step without further purification. The crude product was dried by azeotropic distillation with benzene (5 mL) then dissolved in THF (16 mL) in a flame-dried 20 mL microwave vial with a stir bar. The solution was cooled to 0 °C and LiAlH4 (60 mg, 1.58 mmol, 5.0 equiv) was slowly added. The vial was then sealed and the reaction mixture was heated to reflux and stirred for 3 h. At that time, the reaction mixture was cooled to 0 °C and quenched by the sequential addition of H2O (0.180 mL), 10% aq. NaOH (0.180 mL), and H2O (0.540 mL). The quenched mixture was then stirred at rt until all the solids were white (~12 h), then filtered through Celite with EtOAc, and concentrated to provide crude secondary amine 3.32 (quantitative mass recovery) which was used in the next step without purification. Crude secondary amine 3.32 was dried by azeotropic distillation with benzene (2 x 5 mL). To a flame-dried 20 mL microwave vial with stir bar was added i-Pr2NH (3.2 mL) followed by secondary amine 3.32 as a solution in THF (12.8 mL). The solution was cooled to –78 °C, placed under N2, and n-BuLi (0.76 mL, 2.5 M in hexanes, 6.0 equiv) was added slowly with rapid mixing. The resultant dark red solution was then warmed to rt and the reaction mixture was placed in front of a tungsten-filament lamp (EIKO ELH 300 W, 120 V) at a distance of 2.1 ft and allowed to stir for 6 h. At this time, the light was turned off and the reaction mixture was quenched by the addition of sat. NaHCO3(aq) (30 mL) and extracted with EtOAc (3 x 50 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated. Column

97 chromatography (20:1 CH2Cl2/MeOH with 1% NH4OH, then 9:1 CH2Cl2/MeOH with 1% NH4OH) provided tertiary amine 3.6 as a yellow oil (88 mg, 71% over 3 steps). Secondary Amine 3.32: Rf: 0.31 (20:1 CH2Cl2/MeOH with 1% NH4OH, UV, Dragendorff- 1 Munier stain). H NMR (500 MHz, CDCl3) δ 7.22 (d, J = 8.3 Hz, 1H), 6.74 (dd, J = 8.3, 2.8 Hz, 1H), 6.66 (d, J = 2.7 Hz, 1H), 6.35 (d, J = 12.4 Hz, 1H), 5.81 (dd, J = 12.4, 7.5 Hz, 1H), 5.72 (dd, J = 17.7, 11.0 Hz, 1H), 4.86 (dd, J = 17.7, 1.2 Hz, 1H), 4.77 (dd, J = 11.1, 1.2 Hz, 1H), 4.44 (s, 1H), 3.78 (s, 3H), 3.37 (s, 3H), 3.19 (dd, J = 11.3, 6.5 Hz, 1H), 2.70 – 2.56 (m, 2H), 2.43 (d, J = 11.9 Hz, 1H), 2.25 (d, J = 7.5 Hz, 1H), 2.15 – 2.06 (m, 1H), 1.78 (dd, J = 13.4, 6.9 Hz, 1H), 13 1.53 (tdd, J = 13.7, 6.6, 2.6 Hz, 2H), 0.85 (s, 3H). C NMR (150 MHz, CDCl3) δ 158.3, 142.4, 137.2, 135.6, 132.9, 132.6, 130.4, 117.2, 113.2, 111.8, 87.7, 59.4, 58.1, 55.3, 49.3, 49.1, 44.1, -1 38.3, 34.1, 28.2, 27.2. IR (thin film) ṽmax cm 2926, 2850, 1603, 1463, 1101. HRMS (ESI) calcd + + for [C21H28O2N] ([M+H] ): m/z 326.2115, found 326.2113. Tertiary Amine 3.6: Rf: 0.16 (20:1 CH2Cl2/MeOH with 1% NH4OH, Dragendorff-Munier 1 stain). H NMR (600 MHz, CDCl3) δ 6.95 (d, J = 7.8 Hz, 1H), 6.59 (dd, J = 7.8, 2.4 Hz, 1H), 6.50 (d, J = 2.5 Hz, 1H), 5.62 (dd, J = 17.8, 11.0 Hz, 1H), 4.95 (dd, J = 17.8, 1.3 Hz, 1H), 4.56 (dd, J = 11.0, 1.2 Hz, 1H), 3.85 (d, J = 2.0 Hz, 1H), 3.74 (s, 3H), 3.44 (dd, J = 8.5, 2.2 Hz, 1H), 3.27 (s, 3H), 3.07 (dd, J = 17.8, 8.4 Hz, 1H), 3.02 (dd, J = 11.3, 5.4 Hz, 1H), 2.81 (d, J = 17.9 Hz, 1H), 2.78 (d, J = 12.8 Hz, 1H), 2.56 (d, J = 12.6 Hz, 1H), 2.22 (s, 1H), 1.96 – 1.93 (m, 1H), 13 1.57 – 1.48 (m, 2H), 1.43 – 1.38 (m, 1H), 1.12 (s, 3H). C NMR (150 MHz, CDCl3) δ 158.6, 145.2, 135.5, 135.0, 126.4, 113.5, 110.0, 108.7, 87.6, 67.2, 65.5, 61.3, 57.6, 55.8, 55.4, 55.1, -1 38.3, 32.8, 30.6, 28.8, 23.2. IR (thin film) ṽmax cm 3073, 2936, 1611, 1502, 1096, 1036. HRMS + + (ESI) calcd for [C21H28O2N] ([M+H] ): m/z 326.2115, found 326.2112.

Diels–Alder Adduct 3.15. NH3 (~2.0 mL) was condensed into an oven-dried 20 mL Schlenk flask at –78 °C under Ar. A solution of tertiary amine 3.6 (44 mg, 0.135 mmol) in 1:1 IPA/THF (2.0 mL) was added and the solution was stirred for 20 min. Na(s) (109 mg, 4.73 mmol, 35 equiv) was then added, and the reaction mixture was stirred for 3.5 h. At that time, NH4Cl (250 mg, 4.7 mmol, 35 equiv) was added to quench the reaction, the cooling bath was removed, and the ammonia was allowed to evaporate over 30 min. At that time, 3 N HCl (4 mL) was added and the reaction mixture was stirred for an additional 30 min. The mixture was then poured into sat. NaHCO3(aq) (80 mL) and extracted with EtOAc (3 x 80 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated to provide crude enone 3.37 as a yellow oil which was used in the next step without further purification. Crude enone 3.37 was taken up in anhydrous MeOH (4.5 mL) in a flame-dried 5 mL microwave vial with stir bar, which was sealed and placed under N2. Pyrrolidine (0.5 mL) was then added and the resulting mixture was degassed using three freeze-pump-thaw cycles with liquid nitrogen. The microwave vial was then backfilled with argon and heated to 120 °C for 2 h in the microwave, at which time the reaction mixture was concentrated. Column chromatography (20:1 CH2Cl2/MeOH with 1% NH4OH) gave Diels–Alder adduct 3.15 as an orange oil (17 mg, 0.054 mmol, 40% over 2 steps). 1 Enone 3.37: Rf: 0.16 (9:1 CH2Cl2/MeOH with 1% NH4OH, Dragendorff-Munier stain). H NMR (500 MHz, CDCl3) δ 6.08 (dd, J = 17.7, 11.0 Hz, 1H), 4.98 (dd, J = 17.8, 1.2 Hz, 1H),

4.69 (dd, J = 11.0, 1.2 Hz, 1H), 3.31 – 3.29 (m, 5H), 3.17 (d, J = 2.1 Hz, 1H), 2.98 – 2.94 (m, 1H), 2.66 – 2.58 (m, 2H), 2.53 – 2.45 (m, 5H), 2.33 – 2.28 (m, 1H), 2.23 (s, 1H), 1.93 – 1.89 (m, 13 2H), 1.51 – 1.49 (m, 1H), 1.39 – 1.35 (m, 2H), 1.09 (s, 3H). C NMR (150 MHz, CDCl3) δ 210.1, 143.8, 135.4, 124.9, 106.8, 85.6, 65.6, 65.1, 60.6, 57.1, 56.1, 54.8, 42.3, 38.3, 37.7, 32.44, -1 32.38, 29.4, 28.6, 22.7. IR (thin film) ṽmax cm 2935, 2846, 1717, 1665, 1095. HRMS (ESI) + + calcd for [C20H28O2N] ([M+H] ): m/z 314.2115, found 314.2114. Diels–Alder Adduct 3.15: Rf: 0.13 (9:1 CH2Cl2/MeOH with 1% NH4OH, Dragendorff-Munier 1 stain). H NMR (500 MHz, CDCl3) δ 3.36 (dd, J = 10.2, 5.4 Hz, 1H), 3.31 (s, 3H), 3.22 (s, 1H), 2.95 (s, 1H), 2.70 (dd, J = 14.3, 5.0 Hz, 1H), 2.53 (d, J = 12.5 Hz, 1H), 2.44 (d, J = 12.5 Hz, 1H), 2.27 (d, J = 19.3 Hz, 1H), 2.17 – 2.12 (m, 1H), 2.10 – 2.06 (m, 2H), 2.01 – 1.94 (m, 2H), 1.90 – 1.85 (m, 1H), 1.80 (dd, J = 13.3, 2.9 Hz, 1H), 1.74 – 1.69 (m, 1H), 1.59 – 1.50 (m, 3H), 1.40 – 13 1.25 (m, 3H), 0.98 (s, 3H). C NMR (150 MHz, CDCl3) δ 216.6, 78.0, 72.4, 64.7, 62.5, 62.1, 54.8, 54.5, 49.6, 44.9, 43.3, 42.3, 41.3, 37.7, 36.1, 31.9, 28.5, 27.6, 24.9, 24.7. IR (thin film) ṽmax -1 + + cm 2931, 2872, 2848, 2820, 1723, 1088. HRMS (ESI) calcd for [C20H28O2N] ([M+H] ): m/z 314.2115, found 314.2114.

Keto Alcohol 3.40. To a 1 dram vial containing Diels–Alder adduct 3.15 (9.0 mg, 0.029 mmol) was added a freshly-prepared 6.5% solution of HBr in HOAc (1.0 mL). The solution was briefly heated at 60 °C until the substrate was fully dissolved, then transferred to a 2 mL microwave vial. The reaction mixture was heated in the microwave at 120 °C for 1.5 h, at which time the reaction mixture was cooled to 0 °C. Water (1 mL) was added, followed by ammonium hydroxide until the pH of the solution was greater than 9 (~3 mL). The basified mixture was extracted with CH2Cl2 (3 x 5 mL) and the combined organic layers were dried over Na2SO4, filtered, and concentrated to provide keto acetate 3.41, which was used in the next step without further purification. Crude acetate 3.41 was dissolved in MeOH (1.0 mL) in a 1 dram vial to which was added K2CO3 (40 mg, 0.29 mmol, 10 equiv). The reaction mixture was allowed to stir for 20 h, at which time CH2Cl2 (6 mL), water (3 mL), and brine (3 mL) were added. The reaction mixture was extracted with CH2Cl2 (3 x 6 mL) and the combined organic layers were dried over Na2SO4, filtered, and concentrated. Column chromatography (20:1 CH2Cl2/MeOH with 1% NH4OH, then 9:1 CH2Cl2/MeOH with 1% NH4OH) provided keto alcohol 3.40 as a yellow oil (5.0 mg, 57% over 2 1 steps). Rf: 0.09 (9:1 CH2Cl2/MeOH with 1% NH4OH, Dragendorff-Munier stain). H NMR (400 MHz, CDCl3) δ 4.01 – 3.93 (m, 1H), 3.27 (s, 1H), 3.15 (dd, J = 14.4, 4.8 Hz, 1H), 2.95 (s, 1H), 2.57 (d, J = 12.8 Hz, 1H), 2.45 (d, J = 12.4 Hz, 1H), 2.28 (d, J = 19.6 Hz, 1H), 2.13 (s, 1H), 2.10 (d, J = 19.6 Hz, 1H), 2.04 – 1.93 (m, 3H), 1.87 – 1.83 (m, 2H), 1.76 (dd, J = 9.6, 1.2 Hz, 13 1H), 1.64 – 1.60 (m, 3H), 1.51 – 1.40 (m, 4H), 1.00 (s, 3H). C NMR (100 MHz, CDCl3) δ 216.6, 72.1, 69.1, 65.1, 62.2, 62.1, 56.1, 49.7, 45.0, 43.5, 42.4, 41.3, 37.9, 36.1, 32.4, 31.6, 28.5, -1 28.0, 25.4. IR (thin film) ṽmax cm 3370, 2923, 1718, 1557, 1158, 1076, 1015. HRMS (ESI) + + calcd for [C19H26O2N] ([M+H] ): m/z 300.1958, found 300.1954.

Keto Alkene 3.42. Methyltriphenylphosphonium bromide (120 mg, 0.336 mmol, 5.0 equiv) was dried by azeotropic distillation with benzene (3 x 2 mL) in a flame-dried 10 mL round bottomed flask. A stir bar was added, the flask was placed under nitrogen, and THF (1.0 mL) was added followed by nBuLi (0.10 mL, 2.5M in hexanes, 4.0 equiv). The mixture was stirred for 5 min, before stirring was stopped and the solids were allowed to settle to provide a 0.24 M solution of the Wittig reagent. Meanwhile, keto alcohol 3.40 (5.5 mg, 0.018 mmol, 1.0 equiv) was dried by azeotropic distillation with benzene (2 x 1 mL) and transferred to a flame-dried 2 mL microwave vial with THF (0.5 mL). The solution was placed under nitrogen and the Wittig solution (0.38 mL, 0.24M in THF, 5.0 equiv) was added by syringe, turning the reaction mixture cloudy and yellow. The sealed vial containing the reaction mixture was then moved to an oil bath and heated to 70 °C for 12 h, at which time the vial was removed from the oil bath and cooled to rt. The reaction mixture was quenched with sat. NaHCO3(aq) solution (2 mL) and extracted with DCM (3 x 3 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated to provide hydroxyl alkene 3.38, which was used in the next step without further purification. Crude alkene 3.38 was dissolved in CH3CN (1.0 mL) in a 1 dram vial. Small scoops of MeO Cu(MeCN)4OTf and bpy (~ 1 mg each) were then added, followed by ABNO (1 flake) and NMI (1 drop). This mixture was then stirred, open to the air, at 50 °C for 2 hours, at which time MeO a second portion of Cu(MeCN)4OTf , bpy (~ 1 mg each) and ABNO (1 flake) was added. After stirring at 50 °C for an additional 1 h, the reaction mixture was quenched by the addition of NH4OH (0.5 mL). This mixture was then diluted with DCM (5.0 mL), dried over Na2SO4, filtered, and concentrated. Column chromatography (20:1 CH2Cl2/MeOH with 1% NH4OH) provided keto alkene 3.42 as a yellow oil (3.1 mg, 58% over 2 steps). Rf: 0.33 (9:1 1 CH2Cl2/MeOH with 1% NH4OH, Dragendorff-Munier stain). H NMR (600 MHz, CDCl3) δ 4.67 (d, J = 1.8 Hz, 1H), 4.52 (d, J = 1.8 Hz, 1H), 3.36 (bs, 1H), 3.17 (s, 1H), 2.79 – 2.73 (m, 2H), 2.67 (d, J = 12.6 Hz, 1H), 2.29 – 2.20 (m, 2H), 2.19 – 2.13 (m, 2H), 2.09 (s, 1H), 2.04 – 2.03 (m, 1H), 1.97 – 1.89 (m, 4H), 1.79 – 1.75 (m, 2H), 1.69 (dd, J = 13.8, 3.6 Hz, 1H), 1.48 (dd, 13 J = 13.2, 2.4 Hz, 1H), 1.12 (dt, J = 13.2, 2.4 Hz, 1H), 1.02 (s, 3H). C NMR (150 MHz, CDCl3) δ 216.0, 151.7, 104.2, 80.3, 68.8, 67.2, 66.0, 64.8, 45.7, 45.5, 40.3, 39.0, 38.8, 37.9, 36.2, 34.6, -1 34.5, 34.3, 30.5, 27.5. IR (thin film) ṽmax cm 2920, 2851, 1692, 1031, 800. HRMS (ESI) calcd + + for [C20H26ON] ([M+H] ): m/z 296.2009, found 296.2003.

Cossonidine (3.5). Keto alkene 3.42 (2.0 mg, 0.068 mmol) was dissolved in THF (0.5 mL) in a 1-dram vial and cooled to 0 °C. LiAlH4 (1.3 mg, 0.034 mmol, 5 equiv) was added and the reaction mixture was stirred at 0 °C for 30 min, at which time the reaction was quenched by slow

100 addition of sat. NH4Cl(aq) (0.5 mL) and warmed to rt. The mixture was extracted with CH2Cl2 (3 x 3 mL) and the combined organic layers were dried over Na2SO4, filtered, and concentrated to provide crude axial alcohol 3.39, which was used in the next step without further purification. To a 1 dram vial containing crude axial alcohol 3.39 was added DCM (0.5 mL), followed by SeO2 (3.0 mg, 0.027 mmol, 4 equiv) and TBHP (20 μL, 70% in H2O, 0.20 mmol, 30 equiv). The mixture was allowed to stir at rt for 15 min, at which point the reaction mixture was quenched by the addition of sat. K2CO3(aq) (0.5 mL). This mixture was extracted with CH2Cl2 (3 x 3 mL) and the combined organic layers were dried over Na2SO4, filtered, and concentrated. Column chromatography (9:1 CH2Cl2/MeOH with 1% NH4OH) provided cossonidine (3.5) as a white solid (1.5 mg, 71% over 2 steps). Rf: 0.05 (9:1 CH2Cl2/MeOH with 1% NH4OH, Dragendorff- 1 Munier stain). Partial H NMR (600 MHz, CDCl3) δ 4.98 (s, 1H), 4.96 (s, 1H), 4.22 (s, 1H), 4.02 (s, 1H), 3.40 (s, 1H), 2.55 (d, J = 13.6 Hz, 1H), 2.49 (s, 1H), 2.40 (d, J = 12.5 Hz, 1H), 1.95 + (dd, J = 13.4, 5.0 Hz, 2H), 1.08 (m, 1H), 1.03 (s, 3H). HRMS (ESI) calcd for [C20H28NO2] ([M+H]+): m/z 314.2094, found 314.2110.

3.7 References (1) (a) Wang, F.-P.; Liang, X.-T. In The Alkaloids: Chemistry and Biology; Cordell, G. A., Ed.; Elsevier Science: New York, 2002; Vol. 59; pp 1-280. (b) Wang, F.-P.; Chen, Q.-H.; Liu, X.-Y. Nat. Prod. Rep. 2010, 27, 529-570. (2) (a) Yatsunami, T.; Isono, T.; Hayakawa, I.; Okamoto, T. Chem. Pharm. Bull. 1975, 23, 3030- 3032. (b) Yatsunami, T.; Furuya, S.; Okamoto, T. Chem. Pharm. Bull. 1978, 26, 3199-3207. (3) Cherney, E. C.; Lopchuk, J. M.; Green, J. C.; Baran, P. S. J. Am. Chem. Soc. 2014, 136, 12592-12595. (4) Muratake, H.; Natsume, M. Angew. Chem. Int. Ed. 2004, 43, 4646-4649. (5) Peese, K. M.; Gin, D. Y. J. Am. Chem. Soc. 2006, 128, 8734-8735. (6) Jin, S.-S.; Guo, Q.; Xu, J.; Yu, P.; Liu, J.-H.; Tang, Y.-Q. Chin. J. Nat. Med. 2015, 13, 361- 367. (7) Reina, M.; Gavín, J. A.; Madinaveitia, A.; Acosta, R. D.; de la Fuente, G. J. Nat. Prod. 1996, 59, 145-147. (8) Ulubelen, A.; Desai, H. K.; Srivastava, S. K.; Hart, B. P.; Park, J.-C.; Joshi, B. S.; Pelletier, S. W.; Mericli, A. H.; Mericli, F.; Ilarslan, R. J. Nat. Prod. 1996, 59, 360-366. (9) (a) Corey, E. J.; Howe, W. J.; Orf, H. W.; Pensak, D. A.; Petersson, G. J. Am. Chem. Soc. 1975, 97, 6116-6124. (b) Heathcock, C. H. Angew. Chem. Int. Ed. 1992, 31, 665-681. (10) Tambar, U. K.; Stoltz, B. M. J. Am. Chem. Soc. 2005, 127, 5340-5341. (11) Kisunzu, J. K. A Ring Expansion Strategy Toward the Synthesis of Hetisine-Type C20- Diterpenoid Alkaloids. Ph.D. Dissertation, University of California, Berkeley, CA, 2014. (12) Lebold, T. P.; Gallego, G. M.; Marth, C. J.; Sarpong, R. Org. Lett. 2012, 14, 2110-2113. (13) Griffith, W. P.; Ley, S. V.; Whitcombe, G. P.; White, A. D. J. Chem. Soc., Chem. Commun. 1987, 1625-1627. (14) Lebel, H.; Paquet, V. J. Am. Chem. Soc. 2004, 126, 320-328. (15) Donnelly, D. M. X.; Finet, J.-P.; Rattigan, B. A. J. Chem. Soc. Perkin Trans. 1 1993, 1729- 1735. (16) Bronner, S. M.; Goetz, A. E.; Garg, N. K. J. Am. Chem. Soc. 2011, 133, 3832-3835. (17) Medina, J. M.; Mackey, J. L.; Garg, N. K.; Houk, K. N. J. Am. Chem. Soc. 2014, 136, 15798-15805. (18) Tadross, P. M.; Stoltz, B. M. Chem. Rev. 2012, 112, 3550-3577.

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(19) Dessolin, M.; Guillerez, M.-G.; Thieriet, N.; Guibe, F.; Loffet, A. Tetrahedron Lett. 1995, 36, 5741-5744. (20) Kulbitski, K.; Nisnevich, G.; Gandelman, M. Adv. Synth. Catal. 2011, 353, 1438-1442. (21) Knowles, J. P.; Elliott, L. D.; Booker-Milburn, K. I. Beilstein J. Org. Chem. 2012, 8, 2025- 2052. (22) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4156-4158. (23) Chill, S. T.; Mebane, R. C. Synth. Commun. 2009, 39, 3601-3606. (24) Iida, S.; Togo, H. Tetrahedron 2007, 63, 8274-8281. (25) Vatèle, J.-M. Synlett 2014, 25, 1275-1278. (26) Satoh, T.; Suzuki, S.; Suzuki, Y.; Miyaji, Y.; Imai, Z. Tetrahedron Lett. 1969, 52, 4555- 4558. (27) Heinzman, S. W.; Ganem, B. J. Am. Chem. Soc. 1982, 104, 6801-6802. (28) Baik, W.; Lee, H. J.; Koo, S.; Kim, B. H. Tetrahedron Lett. 1998, 39, 8125-8128. (29) Trost, B. M.; Tang, W. J. Am. Chem. Soc. 2002, 124, 14542-14543. (30) (a) Bhatt, M. V.; Kulkarni, S. U. Synthesis 1983, 249-282. (b) Ranu, B. C.; Bhar, S. Org. Prep. Proc. Int. 1996, 28, 371-409. (c) Weissman, S. A.; Zewge, D. Tetrahedron 2005, 61, 7833- 7863. (31) (a) Jung, M. E.; Lyster, M. A. J. Org. Chem. 1977, 23, 3761-3764. (b) Garg, N. K.; Caspi, D. D.; Stoltz, B. M. J. Am. Chem. Soc. 2004, 126, 9552-9553. (32) Niwa, H.; Hida, T.; Yamada, K. Tetrahedron Lett. 1981, 22, 4239-4240. (33) Hanessian, S.; Guindon, Y. Tetrahedron Lett. 1980, 21, 2305-2308. (34) Guindon, Y.; Yoakim, C.; Morton, H. E. Tetrahedron Lett. 1983, 24, 2969-2972. (35) (a) Jorapur, Y. R.; Chi, D. Y. Bull. Korean Chem. Soc. 2006, 27, 345-354. (b) Boovanahalli, S. K.; Kim, D. W.; Chi, D. Y. J. Org. Chem. 2004, 69, 3340-3344. (c) Park, S. K.; Battsengel, O.; Chae, J. Bull. Korean Chem. Soc. 2013, 34, 174-178. (36) Tang, P.; Chen, Q.-F.; Wang, L.; Chen, Q.-H.; Jian, X.-X.; Wang, F.-P. Tetrahedron 2012, 68, 5668-5676. (37) (a) Lebrun, M.-E.; Marquand, P. L.; Berthelette, C. J. Org. Chem. 2006, 71, 2009-2013. (b) Blakemore, P. R.; Cole, W. J.; Kocienski, P. J.; Morley, A. Synlett 1998, 26-28. (38) Pine, S. H.; Zahler, R.; Evans, D. A.; Grubbs, R. H. J. Am. Chem. Soc. 1980, 102, 3270- 3272. (39) Corey, E. J.; Schmidt, G. Tetrahedron Lett. 1979, 5, 399-402. (40) Steves, J. E.; Stahl, S. S. J. Am. Chem. Soc. 2013, 135, 15742-15745. (41) Trost, B. M., Fleming, I., Eds. Comprehensive Organic Synthesis; Elsevier: Oxford, U. K., 1991; Vol. 8, Section 1.1. (42) Chérest, M.; Felkin, H. Tetrahedron Lett. 1968, 18, 2205-2208. (43) (a) Lansbury, P. T.; MacLeay, R. E. J. Org. Chem. 1963, 28, 1940-1941. (b) Yoon, N. M.; Gyoung, Y. S. J. Org. Chem. 1985, 50, 2243-2450. (c) Brown, H. C.; Krishnamurthy, S. J. Am. Chem. Soc. 1972, 94, 7159-7161. (d) Krishnamurthy, S.; Brown, H. C. J. Am. Chem. Soc. 1976, 98, 3383-3384. (44) Carreño, M. C.; Sanz-Cuesta, M. J.; Colobert, F.; Solladié, G. Org. Lett. 2004, 6, 3537- 3540. (45) Krishnamurthy, S. Aldrichim. Acta. 1974, 7, 55-60. (46) (a) Ley, S. V.; Murray, P. J.; Palmer, B. D. Tetrahedron 1985, 41, 4765-4769. (b) Wang, C.; Gu, X.; Yu, M. S.; Curran, D. P. Tetrahedron 1998, 54, 8355-8370.

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(47) Marth, C. J.; Gallego, G. M.; Lee, J. C.; Lebold, T. P.; Kulyk, S.; Kou, K. G. M.; Qin, J.; Lilien, R.; Sarpong, R. Nature 2015, 528, 493-498. (48) Ikawa, T.; Nishiyama, T.; Shigeta, T.; Mohri, S.; Morita, S.; Takayanagi, S.; Terauchi, Y.; Morikawa, Y.; Takagi, A.; Ishikawa, Y.; Fujii, S.; Kita, Y.; Akai, S. Angew. Chem. Int. Ed. 2011, 50, 5674-5677.

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Appendix 2

NMR Spectra for Compounds Discussed in Chapter 3

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Chapter 4. Exploring a Second-Generation Synthesis of Cossonidine: A Magnesiate- Insertion Route to the 6-7-6 Tricycle

4.1 Introduction While struggling to overcome some of the reproducibility issues in our first-generation synthesis of cossonidine (Chapter 3), we noticed a potentially powerful connection between this route and the aconitine-directed work discussed in Chapter 2. Revisiting our synthesis of vinyl lactone 4.1, we identified that formation of a C–C bond between the aromatic ring and the lactone carbonyl would yield a 6-7-6 tricycle (4.2) very similar to that employed in our total synthesis of cossonidine (Scheme 4-1). From this tricycle, oxidation followed by chemo- and stereoselective methylation should provide diketoaldehyde 4.3, with carbonyl groups at all three carbon atoms that are attached to nitrogen in the hetisine-type natural products. This sets the stage for a triple reductive amination reaction with ammonia to directly provide tertiary amine 4.4, an intermediate in our total synthesis of cossonidine.

Scheme 4-1. Second-generation synthesis of tertiary amine 4.4

4.2 Initial Studies on C–C Bond Formation to Access the 6-7-6 Tricyclic Core We began our investigations in this area by exploring a direct, intramolecular Friedel– Crafts reaction to forge the 6-7-6 tricycle. We were encouraged by the potentially favorable electronics of this system, by virtue of the para-methoxy group on the aromatic ring and the increased electrophilicity of the carbonyl relative to an ester group by virtue of the ketal-type moiety. We began by examining a number of Lewis acids on the initial tricyclic acetal, 4.5 (Table 4-1). While most of the conditions employed on 4.5 returned only starting material, several Lewis acids led to the formation of a new product, tentatively assigned as lactone 4.7 on the basis of LCMS analysis. This product presumably forms through cleavage of the benzyl ether and subsequent cyclization onto the methyl ester to form the lactone ring.

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Table 4-1. Direct Friedel–Crafts reaction attempts on 4.5

Theorizing that vinyl lactone 4.1, lacking both of these functional groups, might be less prone to undesired side reactions, we also explored cyclizations on this substrate. Unfortunately, a screen of Lewis acids led only to recovered starting material or decomposition (Table 4-2).

Table 4-2. Direct Friedel–Crafts reaction attempts on 4.1

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Since a direct Friedel–Crafts reaction did not appear to be a viable path forward, we began to investigate pre-functionalization of the aromatic ring to install a halogen at the para position relative to the methoxy group (4.8). Metal-halogen exchange should generate the corresponding aryl Grignard or lithium (4.9), which should undergo nucleophilic addition into the lactone carbonyl leading to our desired 6-7-6 tricycle (4.2, Scheme 4-2).

Scheme 4-2. Metal-halogen exchange route to 6-7-6 tricycle

Returning to the beginning of the synthesis of vinyl lactone 4.1, we investigated the use of iodinated benzyl pro-nucleophile 4.11 as a means of introducing the iodine atom for eventual metal-halogen exchange. Improving on the two-step literature protocol,1 we were able to access iodinated pro-nucleophile 4.11 in a single step from commercially available 3- methoxyphenylacetic acid (4.10) through treatment with iodine monochloride in methanol (Scheme 4-3).2 Initial electrophilic aromatic substitution presumably forms the intermediate acid iodide, generating an equivalent of HCl which catalyzes the esterification with methanol. Deprotonation with LiHMDS and addition into Diels-Alder adduct 4.12 followed by treatment with HCl provided iodinated acetal 4.13. While the yield is significantly diminished compared to that observed for the deiodinated nucleophile discussed in Chapter 2, tricyclic acetal 4.13 is isolated as predominantly a single diastereomer.

Scheme 4-3. Synthesis of iodinated substrates

The subsequent Krapcho-type decarboxylation reaction proved to be even more challenging to reproduce on the iodinated system. Treatment of 4.13 with LiCl under microwave irradiation provided decarboxylated product 4.14 in only 41% yield, with a significant amount of 131 deiodination observed as well, forming 4.15. Initial analysis of the reaction kinetics suggests that the rate of decarboxylation is comparable to the rate of deiodination under these conditions, with all 4 possible compounds observed by LCMS at partial conversion. Given that we were still able to access reasonable quantities of 4.14 to test our intramolecular nucleophilic addition reaction, and that deiodinated 4.15 could be used in our studies discussed in Chapter 2, we opted to carry our material through this route rather than pursue further optimization at this time.

Rationalizing that the benzyl ether and cyclohexene moieties were unlikely to significantly impact the success or failure of our proposed intramolecular cyclization reaction, we opted to employ 4.14 as our test substrate for the subsequent metal-halogen exchange reaction. Working with Justine deGruyter, an undergraduate student working in our lab on a summer research fellowship, we began screening a wide variety of conditions to form a Grignard or aryl lithium nucleophile from 4.14 (Table 4-3). Attempts to form the aryl Grignard reagent from magnesium metal returned only starting material, while lithium-halogen exchange with n- butyllithium or t-butyllithium led to complex reaction mixtures.3 We also explored magnesium- halogen exchange with iPrMgCl, which resulted either in no reaction at low temperatures or complex mixtures at higher temperatures.4 Synthesis of the corresponding organozinc reagent was also unsuccessful. In 2001, Oshima and co-workers reported the application of magnesium ate complexes for magnesium-halogen exchange.5 These magnesiates were generally shown to possess reactivity between that of an alkyl Grignard and an alkyl lithium, leading to fewer side products while being less sensitive to the electronics of the aromatic system. We were delighted to find that reaction of 4.14 with nBu3MgLi, formed by mixing nBuMgCl and nBuLi in a 1:2 ratio, facilitated magnesium-halogen exchange followed by cyclization to afford 4.16.

Table 4-3. Screen of conditions for metal-halogen exchange/cyclization

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Cyclization product 4.16 exists as an equilibrium mixture of tautomers and stereoisomers, rendering absolute characterization very challenging. While we explored several methods to derivatize and characterize this substrate, these reactions either did not proceed or generated complex mixtures that did not provide conclusive structural data. Nevertheless, we were confident in our ability to forge this C–C bond based on LCMS and crude 1H NMR analysis, and decided to direct our efforts toward further elaboration of our substrate prior to magnesium- halogen exchange.

4.3 Late-Stage Iodination and Elaboration to Diketoaldehyde 4.18 While the current version of our route enabled our initial studies of the C–C bond formation reaction, it presented several challenges for a robust synthesis of the 6-7-6 tricycle. These included the low yield of the iodinated benzyl nucleophile addition into the Diels–Alder adduct and the Krapcho-type decarboxylation which led to significant amounts of deiodination. In addition, the fluxional nature of 6-7-6 tricycle 4.16 would significantly complicate any further studies on this system. Finally, from the perspective of synthetic efficiency, introduction of the iodine atom at the beginning of the route is inelegant and would require re-optimization of previously solved problems. With all of these points in mind, we decided to investigate the late- stage installation of the iodine atom on vinyl lactone 4.1, allowing us to take advantage of the robust synthesis of this compound that we had previously developed. While the more complex nature of vinyl lactone 4.1 relative to 3-methoxyphenylacetic acid (4.10) may introduce additional challenges in reactivity and selectivity, this late-stage functionalization would render this route highly convergent with respect to our previous efforts.

We began by exploring the iodine monochloride conditions previously used to iodinate 3- methoxyphenylacetic acid (4.10). Unfortunately, this iodination protocol provided only a complex mixture of products. We next turned to NIS, a common source of electrophilic iodine, screening a series of activating agents (Table 4-4).6 When taking yield and selectivity into account, the best result was obtained following a procedure reported by Romo, using In(OTf)3 as an activating agent with NIS (Entry 9),6d providing the desired, para-iodinated substrate (4.8) in 38% yield along with a comparable amount of the corresponding ortho isomer (4.17), as well as small amounts of unreacted starting material. While the initial yield of the desired substrate was relatively low, we found that we could readily de-iodinate the undesired isomer through magnesium-halogen exchange with the tributyl magnesiate followed by protonation, regenerating vinyl lactone 4.1 which could be resubjected to the iodination conditions.

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Table 4-4. Screen of iodination conditions

With our desired iodinated substrate in hand, we subjected iodinated vinyl lactone 4.8 to the magnesiate conditions previously identified for facilitating the magnesium-halogen exchange/intramolecular cyclization reaction. To our delight, this reaction proceeded as expected, forging 6-7-6 tricycle 4.2 (Scheme 4-4). Given that this compound also exists as an isomeric mixture and is difficult to purify, we explored conditions for the subsequent oxidation reaction on the crude product. By employing a modified DMP oxidation developed by the Nicolaou group,7 we were able to successfully access diketoaldehyde 4.18 in 59% yield over 2 steps. The structure of 4.18 was verified by X-ray crystallography.

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Scheme 4-4. Synthesis of diketoaldehyde 4.18

4.4 Efforts to Elaborate Diketoaldehyde 4.18 to the Hetisine Core With diketoaldehyde 4.18 in hand, only two steps remain to intercept tertiary amine intermediate 4.4 and complete our second-generation synthesis of cossonidine. First, we need to achieve a chemo- and diastereoselective methylation of the aldehyde to afford 4.3. A triple reductive amination cascade reaction with ammonia would then furnish our previously- synthesized intermediate 4.4 (Scheme 4-5).

Scheme 4-5. Remaining steps to intercept cossonidine intermediate 4.4

Working with Dr. Louis Morrill, a post-doctoral scholar in the group, we began to explore ways to install the C18 methyl group. We investigated numerous conditions for the direct methylation of diketoaldehyde 4.18 as well as several derivatives, including ester 4.19 and nitrile 4.20 (Scheme 4-6). Despite screening several bases and electrophiles and exploring the synthesis of alternative substrates for methylation, we were never successful in our efforts to install a methyl group or equivalent at this position.

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Scheme 4-6. Efforts to install the C18 methyl group

Given the incredibly challenging nature of installing this C18 methyl group, we began to investigate the proposed triple reductive amination cascade reaction on diketoaldehyde 4.18 (Scheme 4-7).8 If successful, this reaction could provide easy access to the des-methyl hetisine- type core, which could prove valuable for structure-activity relationship studies to determine the effect of this methyl group on the bioactivity of the hetisine-type natural products. While not yet explored in great detail, initial experiments conducted by myself, Dr. Louis Morrill, and Melecio Perea, a summer undergraduate researcher, indicate that at least the initial reductive amination steps are feasible. While we have been unable to isolate this product, LCMS analysis suggests we have accomplished a single reductive amination followed by condensation, leading us to propose the generation of secondary enamine 4.23. Further studies are still required to push this reaction to completion and synthesize des-methyl tertiary amine 4.24.

Scheme 4-7. Initial efforts toward a triple reductive amination cascade

4.5 Conclusion Taking advantage of lessons learned from our synthetic studies directed toward aconitine and our initial total synthesis of cossonidine, we have proposed a second-generation synthesis that has the potential to be more robust, higher yielding, and operationally simpler than our previous route. Building from vinyl lactone 4.1, accessed in short order and high yield as described in Chapter 2, we have been able to directly install an iodine atom on the aromatic ring of this substrate. While the selectivity is poor, the undesired isomer can be recycled to the starting material through a deiodination reaction, improving the throughput of material. From this key aryl iodide, we have developed a magnesium-halogen exchange using a trialkyl magnesiate, the product of which undergoes addition into the lactone carbonyl to forge the central 6-7-6 tricycle for our cossonidine synthesis, with carbonyl groups at all 3 nitrogen-

136 bearing centers following oxidation. While we have achieved a rapid synthesis of this tricycle, efforts to successfully elaborate this compound to intercept our first-generation synthesis of cossonidine have been met with difficulty. While efforts to methylate 4.18 and related compounds have been unsuccessful, we are encouraged by initial results from our efforts to effect a triple reductive amination cascade reaction that would stitch up the azabicycle of the hetisine-type alkaloids in a single step. Subsequent efforts will be devoted to successfully implementing this reaction and exploring the synthesis and properties of des-methyl hetisine- type analogues.

4.6 Experimental Procedures and Characterization Data

Iodinated Pro-Nucleophile 4.11. Iodine monochloride (1.8 mL, 36 mmol, 1.2 equiv) was added to methanol (17 mL) at 0 °C, followed by 3-methoxyphenylacetic acid (4.10, 5.0 g, 30 mmol, 1.0

137 equiv). The reaction mixture was heated to 70 °C and stirred for 4 h, at which time the flask was removed from the oil back and allowed to cool to rt. The reaction mixture was quenched with sat. Na2SO3 (20 mL) and extracted with EtOAc (3 x 20 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated. Automated column chromatography (0 → 20% EtOAc in hexanes gradient) provided iodinated pro-nucleophile 4.11 as a viscous oil (7.33 g, 1 80%). H NMR (500 MHz, CDCl3) δ 7.70 (d, J = 8.7 Hz, 1H), 6.86 (d, J = 3.0 Hz, 1H), 6.58 (dd, J = 8.7, 3.0 Hz, 1H), 3.78 (s, 3H), 3.76 (s, 2H), 3.73 (s, 3H), in agreement with previously reported spectral data.1

Iodinated Tricyclic Acetal 4.13. Iodinated pro-nucleophile 4.11 (209 mg, 0.683 mmol, 1.3 equiv) was dried by azeotropic distillation with benzene (2 x 5 mL) then dissolved in THF (2 mL) and cooled to -78 °C. LiHMDS (0.63 mL, 0.630 mmol, 1.0 M in THF, 1.2 equiv) was then added and the solution was stirred at -78 °C for 30 min. At that time, Diels–Alder adduct 4.12 (242 mg, 0.525 mmol) was added dropwise as a solution in THF (4 mL) and the solution was stirred at -78 °C for 2 h. The reaction mixture was quenched by the addition of sat. NH4Cl (5 mL) and allowed to warm to rt, at which point the solution was extracted with EtOAc (3 x 10 mL). The combined organic layers were dried over MgSO4, filtered, and concentrated. The crude alcohol was then dissolved in MeOH (5 mL) and 1 M HCl (0.54 mL) was added. The reaction mixture was stirred at rt for 45 min, at which point the reaction mixture was concentrated. Column chromatography (20% EtOAc in hexanes) provided iodinated tricyclic 1 acetal 4.13 as a colorless oil (97 mg, 29% yield). Rf: 0.63 (1:1 hexanes/EtOAc, KMnO4). H NMR (500 MHz, CDCl3) δ 7.72 (d, J = 9.3 Hz, 1H), 7.35 – 7.28 (m, 6H), 6.61 (dd, J = 8.7, 2.9 Hz, 1H), 6.21 (dd, J = 9.8, 5.6 Hz, 1H), 6.08 (dd, J = 9.7, 6.9 Hz, 1H), 4.44 – 4.33 (m, 3H), 4.17 (t, J = 3.2 Hz, 1H), 4.10 (dd, J = 9.9, 7.8 Hz, 1H), 3.87 (d, J = 5.6 Hz, 1H), 3.76 (s, 3H), 3.69 (d, J = 3.2 Hz, 1H), 3.66 (s, 3H), 3.37 (t, J = 6.0 Hz, 2H), 3.31 (d, J = 9.5 Hz, 1H), 3.21 (s, 3H), 3.03 13 – 2.96 (m, 1H), 1.92 – 1.87 (m, 1H). C NMR (125 MHz, CDCl3) δ 176.6, 170.0, 159.9, 140.3, 138.3, 137.5, 131.9, 129.5, 128.5, 127.7, 127.6, 127.3, 116.8, 115.7, 115.3, 92.3, 76.0, 73.0, 66.6, -1 61.2, 57.2, 55.6, 52.9, 52.6, 50.5, 38.0, 36.8. IR (thin film) ṽmax cm 3448, 2929, 1778, 1739, + + 1587, 1465, 1240, 1087, 986, 732. HRMS (ESI) calcd for [C29H32IO8] ([M+H] ): m/z 635.1136, found 635.1140.

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Aryl Iodide 4.8. To a solution of vinyl lactone 4.1 (2.07 g, 6.00 mmol) in CH3CN (200 mL) under N2 in an aluminum foil-covered flask was added N-iodosuccinimide (1.49 g, 6.60 mmol, 1.1 equiv) and In(OTf)3 (337 mg, 0.60 mmol, 0.10 equiv) and the reaction mixture was stirred at rt in the dark for 36 h. The reaction mixture was then poured into brine (100 mL) and extracted with EtOAc (3 x 100 mL). The combined organic phases were washed with brine, dried over MgSO4, filtered, and concentrated. Column chromatography (30% EtOAc in hexanes) provided aryl iodide 4.8 as a light yellow oil (1.06 g, 2.25 mmol, 38% yield) and a mixture of aryl iodide 4.17 and vinyl lactone 4.1 (31:69 ratio, 1.01 g) which was treated separately afterwards to give a 65% overall yield of aryl iodide 4.8 based on recovered vinyl lactone 4.1. mp: 95 – 97 °C. Rf: 1 0.73 (1:1 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 7.64 (d, J = 8.8 Hz, 1H), 7.03 (d, J = 3.0 Hz, 1H), 6.52 (dd, J = 8.8, 3.1 Hz, 1H), 5.62 (dd, J = 17.4, 10.6 Hz, 1H), 5.12 (d, J = 17.4 Hz, 1H), 5.05 (d, J = 10.6 Hz, 1H), 4.00 (t, J = 8.3 Hz, 1H), 3.87 (dd, J = 117., 8.6 Hz, 1H), 3.75 (s, 3H), 3.41 – 3.30 (m, 5H), 3.27 (dd, J = 6.9, 2.6 Hz, 1H), 2.77 (d, J = 10.4 Hz, 1H), 13 2.49 – 2.40 (m, 1H), 1.71 – 1.58 (m, 4H). C NMR (100 MHz, CDCl3) δ 174.1, 159.8, 139.9, 138.8, 137.0, 117.1, 116.64, 116.55, 115.8, 91.1, 80.7, 72.0, 58.1, 55.51, 55.46, 47.9, 46.9, 34.0, -1 20.4, 17.9. IR (thin film) ṽmax cm 3061, 2937, 2874, 2833, 1774, 1636, 1590, 1567, 1468. + + HRMS (ESI) calcd for [C20H24O5I] ([M+H] ): m/z 471.0663, found 471.0661.

Diketoaldehyde 4.18. To a flame-dried flask was added THF (15 mL) and nBuMgCl (2.0 M in THF, 4.35 mL, 8.70 mmol). The reaction mixture was cooled to 0 °C, nBuLi (2.2 M in hexanes, 7.90 mL, 17.4 mmol) was added, and the reaction mixture was stirred at 0 °C for 10 min to give a solution of nBu3MgLi (0.32 M in THF). To a solution of aryl iodide 4.8 (2.79 g, 5.94 mmol) in THF (60 mL) at -78 °C under N2 was added nBu3MgLi (0.32 M in THF, 22.3 mL, 7.13 mmol, 1.2 equiv) and the reaction mixture was stirred at -78 °C for 30 min, then warmed to 0 °C and stirred at that temperature for 1 h. The reaction mixture was then quenched with sat. NH4Cl(aq) (100 mL) and extracted with EtOAc (3 x 100 mL). The combined organic phases were washed with brine (100 mL), dried over MgSO4, filtered, and concentrated. The crude reaction mixture was then dissolved in benzene (240 mL), followed by the addition of H2O (0.53 mL, 29.7 mmol, 5 equiv) and DMP (12.6 g, 29.7 mmol, 5 equiv). The reaction mixture was stirred at 80 °C for 1

139 h, at which time it was cooled to rt, quenched with sat. NaHCO3(aq) (200 mL) and extracted with EtOAc (3 x 200 mL). The combined organic phases were washed with brine (100 mL), dried over MgSO4, filtered, and concentrated. Column chromatography (25% EtOAc in hexanes) provided diketoaldehyde 4.18 as a white solid (1.21 g, 3.53 mmol, 59% yield). mp: 138 – 140 1 °C. Rf: 0.52 (3:2 hexanes/EtOAc, KMnO4). H NMR (400 MHz, CDCl3) δ 9.73 (s, 1H), 7.19 (d, J = 8.4 Hz, 1H), 6.82 (dd, J = 8.4, 2.4 Hz, 1H), 6.61 (d, J = 2.4 Hz, 1H), 5.59 (dd, J = 17.5, 10.8 Hz, 1H), 5.35 (d, J = 10.8 Hz, 1H), 5.11 (d, J = 17.5 Hz, 1H), 4.38 – 4.35 (m, 1H), 4.27 (d, J = 17.5 Hz, 1H), 3.84 (s, 3H), 3.76 (d, J = 3.9 Hz, 1H), 3.40 (d, J = 17.5 Hz, 1H), 3.27 (s, 3H), 2.32 (dt, J = 12.9, 4.0 Hz, 1H), 2.11 – 1.99 (m, 2H), 1.87 – 1.82 (m, 1H), 1.51 – 1.46 (m, 1H). 13C NMR (100 MHz, CDCl3) δ 205.8, 205.5, 203.8, 162.0, 137.3, 134.5, 131.0, 130.7, 118.7, 114.5, -1 112.9, 79.9, 63.2, 56.5, 55.5, 51.6, 48.2, 44.7, 22.6, 17.2. IR (thin film) ṽmax cm 2931, 2850, + + 1709, 1678, 1604, 1497, 1453. HRMS (ESI) calcd for [C20H23O5] ([M+H] ): m/z 343.1540, found 343.1541.

4.7 References (1) Wipf, P.; Furegati, M. Org. Lett. 2006, 8, 1901-1904. (2) Wariishi, K.; Morishima, S.; Inagaki, Y. Org. Proc. Res. Dev. 2003, 7, 98-100. (3) Bailey, W. F.; Patricia, J. J. J. Organomet. Chem. 1988, 352, 1-46. (4) Knochel, P.; Dohle, W.; Gommermann, N.; Kneisel, F. F.; Kopp, F.; Korn, T.; Sapountzis, I.; Vu, V. A. Angew. Chem. Int. Ed. 2003, 42, 4302-4320. (5) Inoue, A.; Kitagawa, K.; Shinokubo, H.; Oshima, K. J. Org. Chem. 2001, 66, 4333-4339. (6) (a) Carreño, M. C.; Ruano, J. L. G.; Sanz, G.; Toledo, M. A.; Urbano, A. Tetrahedron Lett. 1996, 37, 4081-4084. (b) Castanet, A.-S.; Colobert, F.; Broutin, P.-E. Tetrahedron Lett. 2002, 43, 5047-5048. (c) Leboeuf, D.; Ciesielski, J.; Frontier, A. J. Synlett 2014, 25, 399-402. (d) Zhou, C.-Y.; Li, J.; Peddibhotla, S.; Romo, D. Org. Lett. 2010, 12, 2104-2107. (7) Nicolaou, K. C.; Baran, P. S.; Zhong, Y.-L.; Fong, K. C.; Choi, H.-S. J. Am. Chem. Soc. 2002, 124, 2190-2201. (8) Zhao, H.; Hans, S.; Cheng, X.; Mootoo, D. R. J. Org. Chem. 2001, 66, 1761-1767.

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Appendix 3

NMR Spectra and Crystallography Data for Compounds Discussed in Chapter 4

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X-Ray Crystallography Data for Diketoaldehyde 4.18

A colorless block 0.040 x 0.030 x 0.020 mm in size was mounted on a Cryoloop with Paratone oil. Data were collected in a nitrogen gas stream at 100(2) K using phi and omega scans. Crystal- to-detector distance was 60 mm and exposure time was 5 seconds per frame using a scan width of 2.0°. Data collection was 100.0% complete to 67.000° in . A total of 55022 reflections were collected covering the indices, -11<=h<=11, -14<=k<=14, -18<=l<=18. 3079 reflections were found to be symmetry independent, with an Rint of 0.0562. Indexing and unit cell refinement indicated a primitive, monoclinic lattice. The space group was found to be P 21/c (No. 14). The data were integrated using the Bruker SAINT software program and scaled using the SADABS software program. Solution by iterative methods (SHELXT) produced a complete heavy-atom phasing model consistent with the proposed structure. All non-hydrogen atoms were refined anisotropically by full-matrix least-squares (SHELXL-2014). All hydrogen atoms were placed using a riding model. Their positions were constrained relative to their parent atom using the appropriate HFIX command in SHELXL-2014.

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Table 1. Crystal data and structure refinement for sarpong92. X-ray ID sarpong92 Sample/notebook ID LCM1-059P Empirical formula C20 H22 O5 Formula weight 342.37 Temperature 100(2) K Wavelength 1.54178 Å Crystal system Monoclinic Space group P 21/c Unit cell dimensions a = 9.2809(4) Å = 90°. b = 12.2308(6) Å = 105.217(2)°. c = 15.3442(7) Å  = 90°. Volume 1680.69(13) Å3 Z 4 Density (calculated) 1.353 Mg/m3 Absorption coefficient 0.793 mm-1 F(000) 728 Crystal size 0.040 x 0.030 x 0.020 mm3 Theta range for data collection 4.689 to 68.294°. Index ranges -11<=h<=11, -14<=k<=14, -18<=l<=18 Reflections collected 55022 Independent reflections 3079 [R(int) = 0.0562] Completeness to theta = 67.000° 100.0 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.929 and 0.843 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 3079 / 0 / 228 Goodness-of-fit on F2 1.036 Final R indices [I>2sigma(I)] R1 = 0.0361, wR2 = 0.0917 R indices (all data) R1 = 0.0403, wR2 = 0.0955 Extinction coefficient n/a Largest diff. peak and hole 0.536 and -0.218 e.Å-3

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Table 2. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for sarpong92. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. ______x y z U(eq) ______C(1) 1492(2) 2911(1) 6359(1) 19(1) C(2) 3080(2) 2409(1) 6620(1) 19(1) C(3) 3080(2) 1331(1) 6110(1) 22(1) C(4) 4605(2) 770(1) 6378(1) 27(1) C(5) 5870(2) 1516(1) 6275(1) 26(1) C(6) 5860(2) 2579(1) 6794(1) 22(1) C(7) 4346(1) 3167(1) 6492(1) 18(1) C(8) 4141(2) 3642(1) 5546(1) 19(1) C(9) 2677(2) 4196(1) 5094(1) 21(1) C(10) 1947(1) 4748(1) 5749(1) 20(1) C(11) 1834(2) 5881(1) 5757(1) 22(1) C(12) 1147(2) 6388(1) 6353(1) 23(1) C(13) 524(2) 5769(1) 6926(1) 24(1) C(14) 612(2) 4644(1) 6905(1) 22(1) C(15) 1350(1) 4125(1) 6333(1) 20(1) C(16) 3269(2) 2158(1) 7623(1) 22(1) C(17) 3784(2) 2834(1) 8295(1) 29(1) C(18) 2014(2) 725(1) 4606(1) 31(1) C(19) 7122(2) 3360(1) 6782(1) 25(1) C(20) 1721(2) 8164(1) 5891(1) 34(1) O(1) 412(1) 2318(1) 6273(1) 26(1) O(2) 2655(1) 1610(1) 5171(1) 25(1) O(3) 7185(1) 4277(1) 7074(1) 29(1) O(4) 5156(1) 3622(1) 5181(1) 24(1) O(5) 1028(1) 7496(1) 6429(1) 29(1) ______

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Table 3. Bond lengths [Å] and angles [°] for sarpong92. ______C(1)-O(1) 1.2161(17) C(10)-C(11) 1.389(2) C(1)-C(15) 1.490(2) C(10)-C(15) 1.3971(19) C(1)-C(2) 1.5492(19) C(11)-C(12) 1.392(2) C(2)-C(16) 1.5323(17) C(11)-H(11) 0.9500 C(2)-C(3) 1.5328(19) C(12)-O(5) 1.3665(18) C(2)-C(7) 1.5499(18) C(12)-C(13) 1.395(2) C(3)-O(2) 1.4316(16) C(13)-C(14) 1.379(2) C(3)-C(4) 1.529(2) C(13)-H(13) 0.9500 C(3)-H(3) 1.0000 C(14)-C(15) 1.3997(19) C(4)-C(5) 1.528(2) C(14)-H(14) 0.9500 C(4)-H(4A) 0.9900 C(16)-C(17) 1.311(2) C(4)-H(4B) 0.9900 C(16)-H(16) 0.9500 C(5)-C(6) 1.526(2) C(17)-H(17A) 0.9500 C(5)-H(5A) 0.9900 C(17)-H(17B) 0.9500 C(5)-H(5B) 0.9900 C(18)-O(2) 1.4160(17) C(6)-C(19) 1.515(2) C(18)-H(18A) 0.9800 C(6)-C(7) 1.5377(18) C(18)-H(18B) 0.9800 C(6)-H(6) 1.0000 C(18)-H(18C) 0.9800 C(7)-C(8) 1.5286(18) C(19)-O(3) 1.2030(19) C(7)-H(7) 1.0000 C(19)-H(19) 0.9500 C(8)-O(4) 1.2156(17) C(20)-O(5) 1.4295(19) C(8)-C(9) 1.5139(19) C(20)-H(20A) 0.9800 C(9)-C(10) 1.5103(19) C(20)-H(20B) 0.9800 C(9)-H(9A) 0.9900 C(20)-H(20C) 0.9800 C(9)-H(9B) 0.9900

O(1)-C(1)-C(15) 121.82(12) C(1)-C(2)-C(7) 115.56(11) O(1)-C(1)-C(2) 119.51(12) O(2)-C(3)-C(4) 111.67(11) C(15)-C(1)-C(2) 118.23(11) O(2)-C(3)-C(2) 105.83(11) C(16)-C(2)-C(3) 109.00(11) C(4)-C(3)-C(2) 111.87(11) C(16)-C(2)-C(1) 100.94(10) O(2)-C(3)-H(3) 109.1 C(3)-C(2)-C(1) 109.65(11) C(4)-C(3)-H(3) 109.1 C(16)-C(2)-C(7) 110.86(11) C(2)-C(3)-H(3) 109.1 C(3)-C(2)-C(7) 110.36(11) C(5)-C(4)-C(3) 112.70(12)

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C(5)-C(4)-H(4A) 109.1 C(10)-C(11)-H(11) 120.0 C(3)-C(4)-H(4A) 109.1 C(12)-C(11)-H(11) 120.0 C(5)-C(4)-H(4B) 109.1 O(5)-C(12)-C(11) 124.01(13) C(3)-C(4)-H(4B) 109.1 O(5)-C(12)-C(13) 115.38(13) H(4A)-C(4)-H(4B) 107.8 C(11)-C(12)-C(13) 120.60(13) C(6)-C(5)-C(4) 110.18(12) C(14)-C(13)-C(12) 119.38(13) C(6)-C(5)-H(5A) 109.6 C(14)-C(13)-H(13) 120.3 C(4)-C(5)-H(5A) 109.6 C(12)-C(13)-H(13) 120.3 C(6)-C(5)-H(5B) 109.6 C(13)-C(14)-C(15) 120.58(13) C(4)-C(5)-H(5B) 109.6 C(13)-C(14)-H(14) 119.7 H(5A)-C(5)-H(5B) 108.1 C(15)-C(14)-H(14) 119.7 C(19)-C(6)-C(5) 114.85(12) C(10)-C(15)-C(14) 119.75(13) C(19)-C(6)-C(7) 110.45(11) C(10)-C(15)-C(1) 120.94(12) C(5)-C(6)-C(7) 111.82(11) C(14)-C(15)-C(1) 119.31(12) C(19)-C(6)-H(6) 106.4 C(17)-C(16)-C(2) 125.85(13) C(5)-C(6)-H(6) 106.4 C(17)-C(16)-H(16) 117.1 C(7)-C(6)-H(6) 106.4 C(2)-C(16)-H(16) 117.1 C(8)-C(7)-C(6) 109.86(11) C(16)-C(17)-H(17A) 120.0 C(8)-C(7)-C(2) 115.98(11) C(16)-C(17)-H(17B) 120.0 C(6)-C(7)-C(2) 110.20(11) H(17A)-C(17)-H(17B) 120.0 C(8)-C(7)-H(7) 106.8 O(2)-C(18)-H(18A) 109.5 C(6)-C(7)-H(7) 106.8 O(2)-C(18)-H(18B) 109.5 C(2)-C(7)-H(7) 106.8 H(18A)-C(18)-H(18B) 109.5 O(4)-C(8)-C(9) 120.61(12) O(2)-C(18)-H(18C) 109.5 O(4)-C(8)-C(7) 120.74(12) H(18A)-C(18)-H(18C) 109.5 C(9)-C(8)-C(7) 118.56(11) H(18B)-C(18)-H(18C) 109.5 C(10)-C(9)-C(8) 113.65(11) O(3)-C(19)-C(6) 123.04(13) C(10)-C(9)-H(9A) 108.8 O(3)-C(19)-H(19) 118.5 C(8)-C(9)-H(9A) 108.8 C(6)-C(19)-H(19) 118.5 C(10)-C(9)-H(9B) 108.8 O(5)-C(20)-H(20A) 109.5 C(8)-C(9)-H(9B) 108.8 O(5)-C(20)-H(20B) 109.5 H(9A)-C(9)-H(9B) 107.7 H(20A)-C(20)-H(20B) 109.5 C(11)-C(10)-C(15) 119.70(13) O(5)-C(20)-H(20C) 109.5 C(11)-C(10)-C(9) 119.95(12) H(20A)-C(20)-H(20C) 109.5 C(15)-C(10)-C(9) 120.34(12) H(20B)-C(20)-H(20C) 109.5 C(10)-C(11)-C(12) 119.91(13) C(18)-O(2)-C(3) 113.23(11) 150

C(12)-O(5)-C(20) 117.31(12) ______Symmetry transformations used to generate equivalent atoms:

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Table 4. Anisotropic displacement parameters (Å2x 103)for sarpong92. The anisotropic displacement factor exponent takes the form: -22[ h2a*2U11 + ... + 2 h k a* b* U12 ] ______U11 U22 U33 U23 U13 U12 ______C(1) 23(1) 23(1) 13(1) 0(1) 6(1) -2(1) C(2) 23(1) 17(1) 17(1) 1(1) 7(1) 0(1) C(3) 31(1) 19(1) 18(1) 0(1) 8(1) -1(1) C(4) 38(1) 19(1) 24(1) -1(1) 9(1) 6(1) C(5) 28(1) 25(1) 25(1) -1(1) 8(1) 9(1) C(6) 23(1) 25(1) 19(1) 2(1) 7(1) 5(1) C(7) 20(1) 18(1) 17(1) 0(1) 6(1) 2(1) C(8) 24(1) 17(1) 19(1) -2(1) 8(1) -2(1) C(9) 24(1) 23(1) 18(1) 4(1) 7(1) 0(1) C(10) 16(1) 22(1) 19(1) 2(1) 2(1) 1(1) C(11) 19(1) 24(1) 22(1) 4(1) 2(1) -1(1) C(12) 19(1) 20(1) 26(1) -1(1) -2(1) 1(1) C(13) 19(1) 27(1) 25(1) -5(1) 5(1) 2(1) C(14) 17(1) 26(1) 21(1) 0(1) 5(1) -2(1) C(15) 16(1) 22(1) 19(1) 0(1) 2(1) 0(1) C(16) 25(1) 21(1) 21(1) 4(1) 9(1) 2(1) C(17) 38(1) 32(1) 18(1) 1(1) 9(1) -5(1) C(18) 39(1) 27(1) 25(1) -8(1) 7(1) -2(1) C(19) 19(1) 36(1) 22(1) 5(1) 6(1) 5(1) C(20) 44(1) 21(1) 30(1) 4(1) 1(1) -2(1) O(1) 25(1) 25(1) 26(1) 0(1) 7(1) -6(1) O(2) 35(1) 22(1) 17(1) -2(1) 7(1) -3(1) O(3) 25(1) 27(1) 34(1) 1(1) 8(1) -1(1) O(4) 26(1) 27(1) 23(1) 1(1) 12(1) 2(1) O(5) 32(1) 19(1) 34(1) -1(1) 5(1) 2(1) ______

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Table 5. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 103) for sarpong92. ______x y z U(eq) ______

H(3) 2313 830 6242 27 H(4A) 4811 527 7015 32 H(4B) 4576 112 5998 32 H(5A) 6840 1141 6509 31 H(5B) 5747 1680 5628 31 H(6) 5990 2369 7440 26 H(7) 4391 3801 6910 22 H(9A) 2857 4749 4664 26 H(9B) 1980 3644 4744 26 H(11) 2226 6308 5355 27 H(13) 43 6118 7326 28 H(14) 168 4218 7283 26 H(16) 2987 1449 7770 26 H(17A) 4080 3552 8180 34 H(17B) 3863 2607 8898 34 H(18A) 2753 139 4662 46 H(18B) 1702 974 3977 46 H(18C) 1144 450 4787 46 H(19) 7899 3115 6532 30 H(20A) 2768 7946 5990 50 H(20B) 1671 8932 6062 50 H(20C) 1200 8071 5252 50 ______

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