Biomimetic Total Synthesis of Natural Products

Thesis submitted for the degree of Doctor of Philosophy

Hiu Chun Lam Bsc (Hons.) Chemistry

Department of Chemistry University of Adelaide

Aug, 2017

To my family

II Declaration I certify that this work contains no material which has been accepted for the award of any other degree or diploma in my name, in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. In addition, I certify that no part of this work will, in the future, be used in a submission in my name, for any other degree or diploma in any university or other tertiary institution without the prior approval of the University of Adelaide and where applicable, any partner institution responsible for the joint-award of this degree.

I give consent to this copy of my thesis, when deposited in the University Library, being made available for loan and photocopying, subject to the provisions of the Copyright Act 1968.

I also give permission for the digital version of my thesis to be made available on the web, via the University’s digital research repository, the Library Search and also through web search engines, unless permission has been granted by the University to restrict access for a period of time.

I acknowledge the support I have received for my research through the provision of an Australian Government Research Training Program Scholarship

Hiu Chun Lam Date

III Acknowledgements First, I would like to thank my supervisor Dr. Jonathan George for his guidance during my PhD. I remember when I first joined the George group during my 2nd year of undergraduate studies, Jonathan personally trained me in the laboratory. His passion and enthusiasm in organic chemistry has influenced me greatly during my research studies, and his constant presence in the laboratory has motivated me to work hard. In addition, Jonathan is extraordinarily generous to send me to conferences in Europe and Australia, where I could present my work and learn chemistry. For all the reasons above, my PhD experience has been superb and it is my pleasure to work with Jonathan. Next, I would like to thank the George group, for being supportive throughout my PhD. The regular Wednesday group lunch and Friday drinking sessions have always been enjoyable. To Kevin, thank you for being my mentor. To Justin, thanks for your help with the hyperjapone project. To Henry, thank you for helping me with the verrubenzospirolactone project. I would also like to thank Aaron where we worked on the rhodonoid project together. To all the new additions of the George group (Aaron, Lauren, Stefania and Laura), I wish you all the best in your PhD. To the prodigy JP, I also wish you good luck in your future postgraduate studies. I would like to specifically thank Kevin and Justin, for their company on my roller coaster research journey. Their encouragement has always been helpful. I will cherish the good times we had inside and outside of the laboratory. I would like to thank Professor Andrew Abell to allow me to use his group’s HPLC and polarimeter. To Professor Chris Sumby, thank you for running all the single crystal X-ray crystallography. To the Sumby/Doonan group (particular Michael, Alex, Natasha and Rob), thanks for examining the crystals after we have recrystallized them in the laboratory. I would like to thank eResearch SA to grant my access to the supercomputer Tizard and the database for theoretical calculations. To Professor Greg Metha and Dr. David Huang and their groups, thank you for teaching me to perform the theoretical calculations. To Phil, thank you for running the NMR machines and mass spectrometers. To Dr. Justin Chalker from Flinders University, thank you for giving us chemicals for my research project. I would like to thank the University of Adelaide, it is my privilege to study for a PhD here. At the end, I would like to thank my family for their support, specifically my parents Kent and Daisy, my sister Elva for their unconditional love.

IV Abstract This thesis describes several syntheses of natural products. The overall synthetic approach is to mimic how these secondary metabolites could be derived in Nature, where we aim to gain insights into the biosynthesis of these natural products from the syntheses. The first synthesis of hyperjapones A-I was achieved by an oxidative hetero-Diels-Alder reaction. The transformation of hyperjapone A to hyperajaponols A and C was achieved via an epoxidation and an acid-catalysed rearrangement cascade reaction, forming 4 stereocenters and 2 rings in 1 step. The first synthesis of verrubenzospirolactone was achieved from a Diels-Alder reaction of the polyene in water. Capillobenzopyranol, the proposed biosynthetic precursor of verrubenzospirolactone was also synthesized and converted into verrubenzospirolactone by mirroring our proposed biosynthetic pathway. The first synthesis of rhodonoids C and D, and murrayakonine D was achieved. The key biomimetic step was the acid catalysed rearrangement of an epoxide, forming 3 stereocenters and 2 rings in 1 step. The biomimetic total synthesis of yezo’otogirin C was achieved via an oxidative radical cyclization cascade reaction, forming 2 rings, 2 stereocenters, 1 C=C bond, 1 C-C bond and 1 C-O bond in 1 step.

V List of abbreviations ºC degree Celsius Å Angstrom 1H Hydrogen-1 13C Carbon-13 18-crown-6 1,4,7,10,13,16-Hexaoxacyclooctadecane Ac acetyl AIBN azobisisobutyronitrile aq. aqueous atm atmospheric Bn benzyl br broad Bu butyl c concentration for specific optical rotation measurements CAN ceric ammonium nitrate cm-1 wavenumber conc. correlation spectroscopy CSA 1-(S)-(+)-10-camphorsulfonic acid DBU 1,8-diazobicycloundec-7-ene DDQ 2,3-dichloro-5,6-dicyano-para-benzoquinone DIBAL-H diisobutylaluminium hydride DMF dimethylformamide DMSO dimethyl sulfoxide dr diastereomeric ratio ESI electrospray ionization epi epimer equiv. equivalents Et ethyl g grams h hours HMBC heteronuclear multiple bond correlation spectroscopy HPLC high performance liquid chromatography HRMS high resolution mass spectrometry HSQC heteronuclear single quantum correlation spectroscopy

VI Hz Hertz hν light i-Pr isopropyl IR infrared J coupling constant KHMDS potassium hexamethyldisilazide KO-tBu potassium tert-butoxide LDA lithium diisopropylamine m-CPBA meta-chloroperoxybenzoic acid Me methyl MHz megahertz min minutes Mp melting point Ms mesyl NBS N-bromosuccinimide n-BuLi n-butyllithium NMO N-methylmorpholine NMR nuclear magnetic resonance NOESY Nuclear Overhauser Effect Spectroscopy Nu nucleophile o-DCB 1,2-dichlorobenzene o-quinone methide ortho-quinone methide p-TsOH para-toluenesulfonic acid PCC pyridinium chlorochromate

Pd2(dba)3 tris(dibenzylideneacetone)dipalladium (0) PDC pyridinium dichromate Pd/C palladium on activated carbon

PhI(OAc)2 (Diacetoxyiodo)benzene PhMe toluene

P(o-tol)3 Tri(o-tolyl)phosphine ppm part per million

Rf retention factor

VII Rh2[(R)-RTAD]4 tetrakis[(R)-(–)-(1-adamantyl)-(N- phthalimido)acetate]dirhodium (II) rt room temperature

SN1 unimolecular nucleophilic substitution

SN2 bimolecular nucleophilic substitution TBAF tetrabutylammonium fluoride TBAB tetrabutylammonium bromide TBAI tetrabutylammonium iodide TBDPS tert-butyldiphenylsilyl TBS tert-butyldimethylsilyl TEMPO 2,2,6,6-tetramethyl-1-piperidinyloxy TFA trifluoroacetic acid Tf trifluoromethanesulfonate THF tetrahydrofuran TLC thin layer chromatography TMS trimethylsilyl TPAP tetrapropylammonium perruthenate w/w mass percentage

VIII Table of Contents Declaration ...... III Acknowledgements ...... IV Abstract ...... V List of abbreviations ...... VI

Chapter 1 - General Introduction 1.1. Natural products synthesis ...... 1 1.2. Biomimetic total synthesis of natural products ...... 4 1.3. References ...... 7

Chapter 2 - Biomimetic Total Synthesis of Hyperjapones A-I, and Hyperjaponols A and C 2.1. Introduction ...... 8 2.1.1. Diels-Alder reaction ...... 8 2.1.2. Chemistry of humulene (2.11) ...... 9 2.1.3. Chemistry of caryophyllene (2.30) ...... 11 2.1.4. Isolation of hyperjapones and hyperjaponols ...... 14 2.1.5. Proposed biosynthesis of hyperjapone A (2.49) and hyperjaponols A-C (2.54–2.56)15 2.2. Results and discussion ...... 17 2.2.1. Synthesis of norflavesone (2.58) ...... 17 2.2.2. Biomimetic total synthesis of hyperjapones B (2.50) & D (2.52) ...... 18 2.2.3. Investigation on the hetero-Diels-Alder reaction ...... 19 2.2.4. Biomimetic total synthesis of hyperjapone A (2.49) ...... 22 2.2.5. Biomimetic total synthesis of hyperjaponol C (2.56) ...... 22 2.2.6. Biomimetic total synthesis of hyperjaponol A (2.54) ...... 25 2.2.7. Biomimetic total synthesis of hyperjapones C (2.51) and E (2.53) ...... 28 2.2.8. Isolation of hyperjapones F to I (2.87–2.90) ...... 30 2.2.9. Biomimetic total synthesis of hyperjapones F and G (2.87 & 2.88) ...... 30 2.2.10. Biomimetic total synthesis of hyperjapone H (2.89) ...... 31 2.2.11. Biomimetic total synthesis of hyperjapone I (2.90) ...... 31 2.2.12. Preliminary theoretical calculations of the transition state of cationic alkene cyclization/1,2-shift ...... 32 2.3. Summary ...... 34 2.4. References ...... 36 2.5. Experimental ...... 38 2.5.1. General methods ...... 38 2.5.2. Experimental procedures ...... 39 2.5.3. NMR spectra ...... 61 2.5.4. Tables of 1H and 13C NMR data ...... 119 2.5.5. Single crystal X-ray data ...... 129 2.5.6. Computational Data ...... 131 2.5.7. References ...... 142

IX Chapter 3 - Biomimetic Total Synthesis of Verrubenzospirolactone 3.1. Introduction ...... 143 3.1.1. Diels-Alder reaction of furan ...... 143 3.1.2. Furan oxidation ...... 143 3.1.3. Syntheses and reactions of 2H-chromene ...... 145 3.1.4. Isolation of verrubenzospirolactone ...... 148 3.1.5. Aims of this study ...... 150 3.2. Results and discussion ...... 151 3.2.1. Synthesis of aldehyde 3.48 ...... 151 3.2.2. Synthesis of the Horner-Wadsworth-Emmons reagent 3.47 ...... 153 3.2.3. Biomimetic total synthesis of verrubenzospirolactone (3.38) ...... 153 3.2.4. Synthesis of capillobenzopyranol (3.39) and its oxidation ...... 158 3.2.5. Biomimetic total synthesis of verrubenzospirolactone (3.38) ...... 160 3.2.6. Bioinspired cascade reaction ...... 162 3.3. Summary ...... 167 3.4. References ...... 169 3.5. Experimental ...... 171 3.5.1. General methods ...... 171 3.5.2. Experimental procedures ...... 172 3.5.3. NMR spectra ...... 202 3.5.4. Table of 1H and 13C NMR data ...... 258 3.5.5. Single crystal X-ray data ...... 259 3.5.6. References ...... 263 Chapter 4 - Biomimetic Total Synthesis of Rhodonoids C and D, and Murrayakonine D 4.1. Introduction ...... 264 4.1.1. Isolation of rhodonoids and murrayakinone D ...... 264 4.1.2. Total synthesis of (±)-rhodonoids A (4.1) and B (4.2) by Hsung ...... 265 4.1.3. Proposed biosynthesis of rhodonoids C and D ...... 267 4.1.4. Epoxide cyclisation reaction in the synthesis of siccanin (4.28) by Trost ...... 268 4.2. Results and discussion ...... 270 4.2.1. Biomimetic total synthesis of rhodonoids C and D ...... 270 4.2.2. Investigation on the reactivity of the epoxide 4.18 ...... 273 4.2.3. Synthesis of mahanimbine (4.5) ...... 276 4.2.4. Biomimetic total synthesis of murrayakonine D (4.6) ...... 277 4.2.5. Biomimetic total synthesis of rhodonoids C and D reported by Hsung ...... 278 4.3. Summary ...... 279 4.4. References ...... 280 4.5. Experimental ...... 281 4.5.1. General methods ...... 281 4.5.2. Experimental procedures ...... 282 4.5.3. NMR spectra ...... 306 4.5.4. Tables of 1H and 13C NMR data ...... 346 4.5.5. Single crystal X-ray data ...... 350 4.5.6. References ...... 352

X Chapter 5 - Biomimetic Total Synthesis of Yezo'otogirin C 5.1. Introduction ...... 353 5.1.1. Reductive radical cyclization ...... 353 5.1.2. Oxidative radical cyclization ...... 353 5.1.3. Isolation of yezo’otogirins A-C ...... 355 5.1.4. Proposed biosynthesis of yezo’otogirn A (5.19) ...... 356 5.1.5. Previous biomimetic total synthesis of yezo’otogirin A (5.19) ...... 357 5.1.6. Previous bioinspired total synthesis of yezo’otogirin C (5.21) by Lee ...... 358 5.1.7. Aims of this project ...... 359 5.2. Results and discussion ...... 360 5.2.1. Synthesis of 6-epi-pre-yezo’otogirin C (5.37) ...... 360 5.2.2. Synthesis of yezo’otogirin C (5.21) from 6-epi-pre-yezo’otogirin C (5.37) ...... 361 5.2.3. Synthesis of yezo’otogirin C (5.21) from pre-yezo’otogirin C (5.38) ...... 362 5.2.4. Improved total synthesis of yezo’otogirin C (5.21) reported by Lee...... 365 5.3. Summary ...... 366 5.4. References ...... 367 5.5. Experimental ...... 368 5.5.1. General methods ...... 368 5.5.2. Experimental procedures ...... 369 5.5.3. NMR spectra ...... 381 5.5.4. Table of 1H and 13C NMR data ...... 392 5.5.5. References ...... 393

XI 1. Introduction 1.1. Natural products synthesis Mankind has achieved great discoveries due our curious and adventurous nature, from looking for new species in rain forests and deep oceans, to searching for new subatomic particles in the Large Hadron Collider. For organic chemists, a primary interest is in naturally occurring small molecules. Nature has a great library of these secondary metabolites and we have only discovered a fraction of it. Every week, there are isolation reports of new natural products, varying in structural complexity and biological activity. These organic molecules are not derived by chance or randomness, but by selective pressure in Nature. Therefore, each natural product has its purpose and role that is crucial to the hosts (plants, bacteria, fungi). These species are often limited in resources (precursors or reagents, narrow range of temperature etc.), but still manage to generate molecules with intriguing and fascinating structures.1 To organic chemists, the occurrence of these natural products is an intimidating challenge presented by Nature, and we wonder if we could synthesize them in laboratory. 100 years ago, Professor Robert Burns Woodward was born, who later dedicated his career to natural products synthesis and opened a new era in organic chemistry.2 He synthesized numerous natural products, including cholesterol (1.1)3 and chlorophyll a (1.2) (Figure 1.1).4 5 One of the Woodward’s syntheses is the formal synthesis of vitamin B12 (1.3). Vitamin B12 (1.3) is the most structurally complex of all vitamins; the corrin ring contains 9 stereocenters and 6 of them are contiguous. Woodward and Eschenmoser, along with 99 researchers, together took 11 years to accomplish this great achievement.

H2NOC H2NOC H CONH2 * H2NOC * * * CN N H * N Co N N H * H N N Mg H2NOC * * * N N H H H CONH2 H H CONH CO2Me O HO isopropanol O O phosphate ribose dimethylbenzimidazole

1.1: cholesterol 1.2: chlorophyll a 1.3: vitamin B12 Figure 1.1: Selected examples of Woodward’s syntheses.3,4,5,6,7,8

1 MeO2C O CO2Me MeO2C O O O * * 8 CO2Me O MeO C * A B O 2 NH H O * CO Me * * * N KOt-Bu * 2 O MeO2C * A B N * NH H * N H * N H * N HN O H H * D H * * * C * N MeO2C H D HN H S * * CO Me MeO C * C 2 Br H 2 S CN CO Me 2 CN CO Me 1.4: β-corrnosterone 1.5 1.6: thiodextrolin 1.7 2

P(CH2CH2CN)3 TFA, CH3NO2

MeO2C MeO2C MeO2C O Me2NOC Me2NOC

H H O O * CO2Me S CO2Me S CO2Me * B * * MeO2C * A H MeO2C * MeO2C * NH HN * N H * N H * * N I2, MeOH * N Zn Zn H H * H * H * N N N N N N * D C H H * MeO C * X MeO C * X MeO2C 2 * 2 * 13 H H H CN NC NC CO2Me CO2Me CO2Me 1.10 1.9 1.8

1. PPh3, TFA, DMF 2. CoCl3, THF

O 1. Cl MeO2C MeO2C MeO2C Me2NOC O SH SPh O 2. H 7 H H CO2Me O * * * O 3 8 3 MeO2C MeO2C CN * MeO C 3 * * CN H * CO2Me 2 CN CO2Me N N N N * N N * I , AcOH * * Co 2 Co 10 Co H * H * H * N N N N N N H CN H CN H CN MeO C * MeO2C * MeO C * 2 * 13 * 13 2 * 13 H H H NC NC NC PhS CO2Me CO2Me CO2Me 1.11 1.12 1.13

Raney Ni, CH2N2

H2NOC CONH2 MeO2C MeO2C CO2Me CO2Me H CONH 2 H H * * CO2Me CO Me H2NOC CN * H 2 * N * * * * * N MeO2C CN H 1. H SO MeO2C CN * * liq. NH , NH Cl * N 2 4 * N H Co 3 4 * N 2. N O , NaOAc * N H * ethylene glycol 2 4 N N Co CCl Co H CN H * 4 H * H NOC * N N N N 2 * H CN H CN * MeO2C * MeO2C * * * * 13 H HOOC H H CONH2 HOOC NC CO2Me CO2Me 1.16: cobyric acid 1.15 1.14 Scheme 1.1: Formal synthesis of vitamin B12 by Woodward and Eschenmoser.5,7,8

2 The synthesis of B12 began from preparation of β-corrnosterone (1.4) in 32 steps, which possessed 6 contiguous asymmetric carbon atoms and the A-D ring of B12. β-Corrnosterone (1.4) was then converted into 1.5, which was ready to be coupled with thiodextrolin (1.6). Thiodextrolin (1.6) was prepared in 21 steps, and it existed as two diastereoisomers differing on the stereocenter C-8 in ring B. The two diastereoisomers could be separated but the C-8 stereocenter was readily epimerised. Hence, thiodextrolin (1.6) was used as a mixture in the coupling step. The thiolactam of thiodextrolin (1.6) was deprotonated using KOt-Bu, which then attacked the bromide 1.5 to give 1.7. 1.7 was transformed into 1.8 by TFA which united the A-D ring and the B-C ring with a C-C bond. However, in this process, the stereochemistry at C-13 on ring C was lost. 1.8 was then converted into 1.9 which contained a thiolactam and a terminal alkene. Oxidative cyclization of 1.9 using I2 afforded 1.10. 1.10 was then rearranged to the corrin ring by TFA and the Zn metal center was replaced by Co ion to give 1.11. During the transformation of the thioether 1.10 to the corrin ring, the stereocenter C-3 on ring A was lost. Thus, a total of 3 stereocenters in 1.11 were lost in the sequence of these reactions and 1.11 was in fact in a mixture of 8 diastereoisomers. 1.11 underwent an oxidative cyclization to give 1.12 which contained a lactone. The formation of the lactone corrected the stereochemistry at C-8 because of the amide at C-7 dictated the stereochemistry at C-8 during the cyclization. The lactone ring also provided steric hindrance to avoid substitution occurring at C-10 in the next step. The substitution was conducted using benzyl chloromethyl ether, followed by substitution of chloride to phenylthiol ether which gave 1.13. The presence of phenylthiol ether allowed the separation of the mono-substituted and the di-substituted compounds. The phenylthiol ethers 1.13 was then reduced to methyl group by Raney Ni; in the same step, the lactone on ring C was also cleaved and methylated to give the methyl ester 1.14. At this stage, HPLC and high pressure liquid-liquid partition chromatography were used to isolate 1.14 with the desired stereochemistry at C-3. The two diastereoisomers differing at C-13 could be separated at this point but it was not important because in the next step, when the cyanide group was hydrolysed into an amide group using

H2SO4, the stereocenter C-13 would be epimerised and hence the two diastereoisomers of 1.14 (at C-13) were used in the hydration step. The amide with the correct stereochemistry would then be isolated from HPLC, followed by conversion to carboxylic acid 1.15 using nitrogen tetroxide. All methyl esters on 1.15 were converted into amide by liquid NH3 with catalytic NH4Cl to give cobryic acid (1.16). Cobryic acid (1.16) was previously converted 9 into Vitamin B12 (1.3) by Friedrich. This concluded the formal synthesis of B12 by Woodward and Eschenmoser.5,7,8

3 Recently, I was lucky to meet Professor Ian Fleming and Professor Leon Ghosez, and they were very kind to share their stories, particularly about working with Professor Woodward as postdoctoral researchers. Their memorable time included discussing chemistry with Professor Woodward, and witnessing him tremendously excited (no less than the researchers) when someone produced perfect crystals. Today, I am grateful to work with my supervisor Dr. Jonathan George, and had experienced great satisfaction when we synthesized and isolated natural products in the laboratory, especially when the NMR data from the isolation and the synthetic sample is perfectly matched. I believe this is the ultimate motivation for organic chemists to pursue total synthesis.

1.2. Biomimetic total synthesis of natural products A natural product can be synthesized by numerous possible pathways, and we are only limited by our imagination. Our group is interested in synthesizing these organic molecules by mimicking how they could be derived in Nature, specifically if they are generated from a pre-disposed, non-enzymatic biosynthesis. Assuming the biosynthetic hypothesis is correct, organic chemists should be able to reproduce the chemistry in a laboratory setting.

N CO2H COH heat +CO2 MeNH O 2 +H2O COH CO2H O 1.17: succinaldehyde 1.18: methylamine 1.19: 3-oxopentanedioic acid 1.20: tropinone Scheme 1.2: Biomimetic total synthesis of tropinone (1.20) reported by Robinson.10

Sir Robert Robinson reported the first example of a biomimetic total synthesis 100 years ago in the synthesis of tropinone (1.20), which was prepared from a three-component one-pot synthesis (Scheme 1.2). Not only does the molecular complexity increase dramatically in one step, but the connection of the new rings and the relative stereochemistry in the molecule are all correctly installed in this reaction. Thus, the initial phase of biomimetic synthesis would require speculation on how rings and stereocenters of natural products are derived from their corresponding biosynthetic precursors. Subsequently, these compounds would be synthesized while mirroring the proposed biosynthesis using simple chemical reagents. At the end of the synthesis, organic chemists would gain insights onto the biosynthetic pathways of these natural products, as a feedback to the biosynthetic proposal.

4 While the biosynthetic precursors may not be synthesized using a biomimetic approach, we aim to develop concise methods to construct those molecules. For instance, we would avoid unnecessary redox reactions, and minimise functional group and protecting group manipulations. Since the report of tropinone synthesis by Robinson, organic chemists have been utilising this philosophy and strategy to synthesize natural products, as the biomimetic approach is arguably the quickest and most economical way to access a natural product. One recent example is the biomimetic total synthesis of homodimericin A (1.28). (±)- Homodimericin A (1.28) was isolated by Clardy in 2016 from a pair of species, bacteria Streptomyces sp. 4231 and fungi Trichoderma harzianum.11 Homodimericin A (1.28) was isolated as a racemate and hence suggesting it is likely to be derived via a pre-disposed, non- enzymatic biosynthesis. As outlined in our proposed biosynthesis (Scheme 1.3), oxidation of 1.21 could give quinone 1.22. Dimerisation of 1.22 via a Michael reaction could afford 1.23, followed by a second Michael reaction to give 1.24. Oxidation of 1.24 could give 1.25, which then undergoes intramolecular Diels-Alder reaction to give 1.26. Tautomerisation of the enol 1.26 (highlighted in blue) could afford 1.27. Intramolecular aldol reaction of 1.27 could then afford homodimericin A (1.28). The isolation chemists also proposed a similar biosynthesis with a different order of Michael reaction and oxidation but the overall proposal is the same.11 In June 2017, the biomimetic total synthesis of homodimericin A (1.28) was reported by three independent groups (Tang12, Wang13, Yang14). Each reported a unique way to synthesize the monomer 1.21, but the chemistry to achieve homodimericin A (1.28) was identical. This showcases biomimetic total synthesis of natural products is highly robust, and also remarkably attractive to organic chemists as shown in all three reports.

5 OH O H HO HO HO Michael addition/ O O oxidation dimerisation HO OH OH 1.22 OH O OH O O O 1.21 HO O

O H 1.23 O 1.22 Michael addition

OH O O O O O O Diels-Alder HO OH HO HO OH reaction oxidation

O OH OH H H O OH O O O OH O O O

1.26 1.25 1.24

tautomerisation

O O O HO OH O formal HO OH aldol reaction O O O O H O O OHO 1.27 1.28: (±)-homodimericin A Scheme 1.3: Our proposed biosynthesis of homodimericin A (1.28). Also later reported by Tang12 and Wang13.

6 1.3. References 1. Nicolaou, K. C.; Vourloumis, D.; Winssinger, N.; Baran, P. S. Angew. Chem. Int. Ed., 2000, 39, 44. 2. Halford, B. Chemical and Engineering News, 2017, 95. 3. Woodward, R. B.; Sondheimer, F.; Taub, D. J. Am. Chem. Soc., 1951, 73, 3548. 4. Woodward, R. B.; Ayer, W. A.; Beaton, J. M.; Bickelhaupt, F.; Bonnett, R.; Buchschacher, P.; Closs, G. L.; Dutler, H.; Hannah, J.; Hauck, F. P.; Ito, S.; Langemann, A.; Legoff, E.; Leimgruber, W.; Lwowski, W.; Sauer, J.; Valenta, Z.; Volz, H. J. Am. Chem. Soc., 1960, 82, 3800. 5. Woodward, R. B. Angew. Chem. Int. Ed., 1963, 75, 871. 6. Woodward, R. B. Science, 1966, 153, 487. 7. Woodward, R. B. Pure and applied chemistry. Chimie pure et appliquee, 1968, 17, 519. 8. Woodward, R. B. Pure and applied chemistry. Chimie pure et appliquee, 1971, 25, 283. 9. Friedrich, W.; Gross, G.; Bernhauer, K.; Zeller, P. Helv. Chim. Acta., 1960, 43, 704. 10. Robinson, R. J. Chem. Soc., Trans., 1917, 111, 762. 11. Mevers, E.; Sauri, J.; Liu, Y.; Moser, A.; Ramadhar, T. R.; Varlan, M.; Williamson, R. T.; Martin, G. E.; Clardy, J. J Am Chem Soc, 2016, 138, 12324. 12. Feng, J.; Lei, X.; Guo, Z.; Tang, Y. Angew. Chem. Int. Ed., 2017, 56, 7895. 13. Ma, D.; Liu, Y.; Wang, Z. Angew. Chem. Int. Ed., 2017, 56, 7886. 14. Huang, J.; Gu, Y.; Guo, K.; Zhu, L.; Lan, Y.; Gong, J.; Yang, Z. Angew. Chem. Int. Ed., 2017, 56, 7890.

7 Chapter 2 Biomimetic Total Synthesis of Hyperjapones A-I, Hyperjaponols A and C 2.1. Introduction 2.1.1. Diels-Alder reaction

Diels-Alder reaction

"dienophile" "diene" Figure 2.1: An illustration of Diels-Alder reaction.

The Diels-Alder reaction is a classic reaction in organic synthesis, where by a diene and a dienophile undergo a concerted cycloaddition to give a 6-membered ring (Figure 2.1).1 There are numerous examples in the literature where Diels-Alder reactions are involved in natural product syntheses.2,3,4 For example, in the total synthesis of (–)-furaquinocin C (2.6) reported by Smith5 (Scheme 2.1), two silyl enol ethers were generated from the deprotonation of the ketone 2.1 to give diene 2.3. Diene 2.3 and dienophile 2.4 then underwent a Diels-Alder reaction to give intermediate 2.5, followed by elimination, rearomatization and desilylation to give (–)-furaquinocin C (2.6) in 1 step.

LDA, TMSCl O O O THF, –78 °C LDA, TMSCl O O TMSO

O OTMS OTMS 2.3 2.1 2.2

TMSO O O O elimination/ O O rearomatization/ Diels-Alder Br O desilylation Br reaction TMSO MeO MeO OH MeO OTMS O OTMS O O 2.6: (−)-furaquinocin C 2.5 2.4 2.3 51% Scheme 2.1: Total synthesis of (–)-furaquinocin C (2.6) by Smith.5

A reaction is classified as a hetero-Diels-Alder reaction when it involves one or more heteroatoms during the cycloaddition. An example is the total synthesis of variecolortide A (2.10) by Trauner6 (Scheme 2.2), where the heterodiene hydroxyviorcristin (2.7) and the dienophile isoechinulin B (2.8) underwent a hetero-Diels-Alder reaction to afford intermediate 2.9. 2.9 was oxidized by air in the same pot to give (±)-variecolortide A (2.10).6 More recent examples of hetero-Diels-Alder reactions in natural product synthesis have been summarised elegantly by Heravi.7

8 OH OH O OH OH O OH O OH 2.7: hydroxyviorcristin

HO HO HO O O oxidation/ O O o-DCB, air, 180 °C O tautomerisation O NH NH NH Diels-Alder reaction HN HN HN O O O

HN HN HN 2.8: isoechinulin B

2.9 2.10: (±)-variecolortide A 48% Scheme 2.2: Total synthesis of variecolortide A (2.10) by Trauner.6

2.1.2. Chemistry of humulene (2.11)

4 5 2 1 5 4 2 1 8 9 9 8

2.11: humulene Figure 2.2: Structure of humulene (2.11).

Humulene (2.11) is a cyclic sesquiterpene natural product containing three alkenes (Figure 2.2). Each alkene possesses different reactivity, as shown in an epoxidation study by Fujita (Scheme 2.3). When humulene (2.11) was treated with one equivalent of m-CPBA, the major product of the reaction was epoxide 2.12. The results from this study suggested that the Δ1,2-alkene in humulene (2.11) is the most reactive, followed by the Δ8,9-alkene and lastly the Δ4,5-alkene.8 The hypothesis is in good agreement with the results from the diepoxidation of humulene (2.11), which afforded epoxide 2.15 (Scheme 2.3).

m-CBPA (2 eq.) 1 m-CBPA (1 eq.) O 5 4 2 O CH2Cl2,−10 °C to rt CH2Cl2,−10 °C to rt O 9 + + O 8 O

2.15 2.11: humulene 2.12 2.13 2.14 (30%) (75%) (14%) (5%) Scheme 2.3: Epoxidation of humulene (2.11) by Fujita.8

In addition, humulene epoxide 2.13 has been shown to undergo an acid catalysed rearrangement reaction. Roberts reported a synthesis of 2.19 by treating humulene epoxide 2.13 with SnCl4 in

CH2Cl2 at –60 ºC. The proposed mechanism starts from the isomerisation of alkene 2.13 to give 2.16, followed by an alkene cyclisation to form a 6-membered ring 2.17, which then undergoes a

9 1,2-alkyl shift to give the tertiary carbocation 2.18. Finally, a 1,2-hydride shift followed by deprotonation to give 2.19 (Scheme 2.4).9

H SnCl4, CH2Cl2 alkene −60 °C cyclization isomerisation O O HO

2.13 2.16 2.17

1,2-alkyl shift

1,2-H shift/ deprotonation H

HO HO

2.19 2.18 25% Scheme 2.4: Synthesis of 2.19 from acid catalysed rearrangement from 2.13 reported by Roberts.9

Humulene (2.11) has also been used as a dienophile in hetero-Diels-Alder reactions, such as the biomimetic total syntheses of guajadial B (2.23) by Liu10 (Scheme 2.5) and lucidene (2.27) by Baldwin11,12 (Scheme 2.6). Guajadial B (2.23) was synthesized in a three-component, one-pot reaction, presumably derived from the formation of o-quinone methide intermediate 2.22 via a Knoevenagel condensation between benzaldehyde (2.20) and 2.21, followed by hetero-Diels-Alder reaction with humulene (2.11). The biomimetic synthesis afforded 45% yield of guajadial B (2.23), along with 19% yield of 2.24.

CHO CHO O OH O OH NaOAc, AcOH, 80 °C + + H CHO CHO OH O H OH

2.11: humulene 2.20: benzaldehyde 2.21 2.11: humulene 2.22 3 equiv. 2 equiv.

hetero-Diels-Alder reaction

CHO CHO O OH O OH + CHO CHO H H OH OH

2.23: (±)-guajadial B 2.24 45% 19% Scheme 2.5: Biomimetic total synthesis of guajadial B (2.23) by Liu.10

10 Similarly, lucidene (2.27) was synthesized by heating 2.25 and humulene (2.11) in a sealed tube, where 2.25 first underwent elimination to give o-quinone methide intermediate 2.26, followed by hetero-Diels-Alder reactions on the Δ1,2-alkene and Δ8,9-alkene of humulene (2.11) to give lucidene (2.27) (Scheme 2.6). Both monoadduct 2.29 and isolucidene (2.28) were also isolated in the same reaction.11,12 The synthesis of lucidene (2.27) and guajadial B (2.28) indicates the hetero-Diels- Alder reaction between humulene (2.11) and o-quinone-methide is highly diastereoselective and regioselective.

2 HO xylene, 170 °C O 1 HO 8 seal tube 9 +

2.25 O 2.26 2.11: humulene 2.05 equiva.

hetero-Diels-Alder reaction

O O

O H H + + H H O H O

2.29 2.27: (±)-lucidene 2.28: (±)-isolucidene 28% 17%, 2.27/2.28 = 2.5:1 Scheme 2.6: Biomimetic total synthesis of lucidene (2.27) by Baldwin.11,12

2.1.3. Chemistry of caryophyllene (2.30)

H 4

5 8 H 15 2.30: caryophyllene Figure 2.3: Structure of caryophyllene (2.30).

Caryophyllene (2.30) is an enantiopure bicyclic sesquiterpene natural product with two alkenes (Figure 2.3). Caryophyllene (2.30) could also undergo epoxidation, where the Δ4,5-alkene can be oxidized spontaneously under air to give caryophyllene oxide (2.31).13 The trans-Δ4,5-alkene in the 9-membered ring of caryophyllene (2.30) is highly reactive because the ring strained in caryophyllene (2.30) would be released after the reaction. Furthermore, caryophyllene oxide (2.31) could also rearrange under reductive conditions to give 2.33 as the predominate product (Scheme 2.7).14 11 H H H m-CPBA, CH Cl , rt 2 2 O + O H H H 2.30: caryophyllene 2.31: caryophyllene oxide 2.32 55%, 2.31:2.32, d.r. 4:1

Cp2TiCl2, Mn, 2,4,6-collidine TMSCl, THF, rt

H H H H + + + H OH H OH H OH H OH

2.33 2.34 2.35 2.36 90%, 2.33:2.34:2.35:2.36, d.r. 20:9:5:1 Scheme 2.7: Reductive acid-catalysed rearrangement reaction of caryophyllene oxide (2.31) by Barrero.14

Alternatively, caryophyllene oxide (2.31) could be ring opened by tetracyanoethylene

(NC)2C=C(CN)2 to give 2.37 and 2.38 (Scheme 2.8). The authors hypothesized that the low energy

π* orbital in (NC)2C=C(CN)2 could interact with the electron-rich epoxide, followed by fragmentation of epoxide to generate alkenes 2.37 and 2.38.15

H (NC)2C=C(CN)2 H H acetone, reflux O OH + OH

H H H

2.31 2.37 2.38 13% 71%

Scheme 2.8: Cleavage of caryophyllene oxide (2.31) using (NC)2C=C(CN)2 reported by Marcias-Sanchez.15

Unsurprisingly, caryophyllene (2.30) has also been used as a dienophile in hetero-Diels-Alder reactions. In the synthesis of cytosporolide model 2.41 by the George group, o-quinone methide

2.40 was generated from 2.39 and HC(OEt)3, which then underwent a hetero-Diels-Alder reaction with caryophyllene (2.30) to give 2.41 (Scheme 2.9).16 This synthesis of 2.41 supported the structural reassignment of cytosporolides A–C.16 The total synthesis of cytosporolide A (2.45) was later completed by Takao (Scheme 2.10), in which the key step was the hetero-Diels-Alder reaction between a highly functionalised diene 2.43 and dienophile 2.42 to give 2.44.17 Deprotection of 2.44 gave cytosporolide A (2.45) in 63% over two steps.

12 MeO O MeO O MeO O H O OH HO OH H O OH HC(OEt)3, TFA hetero-Diels-Alder 100 °C reaction H H H O HO H O

2.39 2.30: caryophyllene 2.40 2.41 53% Scheme 2.9: Synthesis of cytosporolide model 2.41 by the George group.16

HO O OTES HO O OH HO O TESO HO O OH O OH O OH hetero-Diels-Alder OH 1. DIBAL, CH2Cl2, –78 °C OH reaction 2. HF·pyridine, THF, rt H H H H H OMe H 63% over 2 steps H O O O OBz OMe OH OMe OBz C7H15 C7H15 C7H15 2.42 2.43 2.44 2.45: (+)-cytosporolide A Scheme 2.10: Total synthesis of (+)-cytosporolide A (2.45) by Takao.17

In a similar fashion, caryophyllene (2.30) was also incorporated in the syntheses of guajadial (2.46) and psidial A (2.47) by Lee and coworkers.18 o-Quinone methide 2.22 was generated from Knoevenagel condensation of benzaldehyde (2.20) and 2.21, followed by a hetero-Diels-Alder reaction with caryophyllene (2.30) to give a mixture of guajadial (2.46) and psidial A (2.47), alongside 2.48 (Scheme 2.1).18

CHO H O OH H CHO 5% w/w PTS (aq) HO OH 100 °C CHO + + H OH H CHO O H OH 2.30: caryophyllene 2.22 2.30: caryophyllene 2.20: benzaldehyde 2.21 hetero-Diels-Alder reaction

H CHO H CHO H CHO 1 O OH 1 O OH 1 O OH 9 9 9 H 1' H 1' H 1' CHO + CHO + CHO H H H OH OH OH

2.46: guajadial 2.47: psidial A 2.48

25%, 2.46:2.47:2.48, d.r. 3:1:1 *PTS = PEG-600/α-Tocopherol-based diester of Sebacic acid Scheme 2.11: Biomimetic total synthesis of guajadial (2.46) and psidial A (2.47) by Lee and coworkers.18

The 9-membered ring in caryophyllene (2.30) is flexible and it can adopt different conformations. Calculations from Toma suggested a 33:44:23 ratio of the βα:αα:ββ conformations in caryophyllene

13 (2.30) (Figure 2.4).19 2.48 is presumably generated from the less abundant ββ caryophyllene conformer, whereas guajadial (2.46) and psidial A (2.47) are derived from the more abundant βα and αα conformers. Note that reacting with βα and αα conformers does not change the relative stereochemistry between C-1 and C-9 with respect to the Δ4,5-alkene in caryophyllene (2.30). The stereochemistry difference at C-1’ in guajadial (2.46) and psidial A (2.47) can be derived from the steric/kinetic effect of the E/Z isomer of o-quinone methide 2.22.

H 4 9 9 1 5 1 5 5 1 1 1 9 9 4 9 H 4 4 4 5 5 βα αα ββ αβ 2.30: caryophyllene 33% 44% 23% 0% Figure 2.4: Conformers of caryophyllene (2.30) and theirs theoretical population calculated by Toma.19

2.1.4. Isolation of hyperjapones and hyperjaponols

H H H O O O O O O O O H H H H H H H H OH O OH O OH O OH O (±)-2.49: hyperjapone A 2.50: hyperjapone B 2.51: hyperjapone C 2.52: hyperjapone D

O O O O H H O O O O H HO H HO H HO H OH O OH O H H OH O OH O (±)-2.54: hyperjaponol A (±)-2.55: hyperjaponol B (±)-2.56: hyperjaponol C 2.53: hyperjapone E Figure 2.5: Hyperjapones A-E (2.49–2.53)20 and hyperjaponols A-C (2.54–2.56).21

Hyperjapones A-E (2.49–2.53) are structurally related meroterpenoids that were isolated from Hypericum japonicum by Xu (Figure 2.5).20 Hyperjapone A (2.49) is a racemic molecule containing an 11/6/6 ring system, whereas all hyperjapones B-E (2.50–2.53) are enantiopure and possess a 4/9/6/6 ring system. Shortly after the isolation of hyperjapones, Zhang reported the isolation of hyperjaponols A-C (2.54–2.56) from the same plant (Figure 2.5).21 Hyperjaponol C (2.56) contains a 5/7/6/6 ring system with an unusual trans-isodaucane structure, and is the most stereochemically complex among the three hyperjaponols. The racemic nature of hyperjaponols (2.54–2.56) implies the presence of a non-enzymatic, highly pre-disposed biosynthesis.

14 2.1.5. Proposed biosynthesis of hyperjapone A (2.49) and hyperjaponols A-C (2.54– 2.56)

HO OH HO O 2 O O hetero-Diels-Alder trimethylation oxidation 1 reaction humulene (XX) OH O OH O OH O 2.57 2.58: norflavesone 2.11: humulene 2.59

2.49: (±)-hyperjapone A

O O O O

O OH O OH OH O OH H cation-alkene H ring-opening H O H H H cyclization H 5 4 H of epoxide H H epoxidation H H

H H 8 HO H HO O 9 2.62 2.61 2.60 2.49: (±)-hyperjapone A concerted, asynchronous cation- alkene cyclization/1,2-alkyl shift − H 1,2-alkyl shift

O O O O

OH OH O O O OH OH H H H H O H H H H − H H H H H +

HO H HO H HO H HO H 2.63 2.56: (±)-hyperjaponol C 2.54: (±)-hyperjaponol A 2.55: (±)-hyperjaponol B Scheme 2.12: Proposed biosynthesis of hyperjaponols A-C (2.54–2.56).

We propose the biosynthesis of hyperjaponols A-C (2.54–2.56) is derived from hyperjapone A (2.49) (Scheme 2.12). Our proposed biosynthetic pathway begins from the trimethylation of acylphloroglucinol 2.57, which gives norflavesone (2.58), a natural product isolated from a flowering plant Lepsospermum scoparium.22 Oxidation of norflavesone (2.58) would give a heterodiene intermediate 2.59, which undergoes a Diels-Alder reaction with humulene (2.11) to form hyperjapone A (2.49). From the examples shown in the synthesis of lucidene (2.27)11,12 and guajadial B (2.23),10 we predict that the hetero-Diels-Alder reaction would take place onto the Δ1,2- alkene of humulene (2.11). The X-ray crystal structure of hyperjapone A (2.49) shows that the Δ8,9-alkene adopting a conformation such that one face of the alkene is exposed, while the other face is not accessible due to the steric hindrance of the macrocycle.20 Therefore, the epoxidation of hyperjapone A (2.49) should take place on the exposed face of Δ8,9-alkene to give 2.60. Epoxide 2.60 could be ring- opened by acid to give tertiary carbocation 2.61, followed by cyclization onto the Δ4,5-alkene to form a 6/7 membered ring system and a secondary carbocation 2.62.9 We predict that the cyclization of 2.61 should be diastereoselective based on the geometry and the conformation of the macrocycle of 2.61. A stereoselective 1,2-alkyl shift of 2.62 could generate the tertiary carbocation 2.63. The loss of a proton from the methyl group in carbocation 2.63 could afford hyperjaponol C 15 (2.56), while deprotonation of carbocation 2.61 would generate hyperjaponol A (2.54) or hyperjaponol B (2.55). In regards to the alkene cyclisation of carbocation 2.61 and the 1,2-alkyl shift in our proposed biosynthesis of hyperjaponol C (2.56), it is possible that these processes might occur in a concerted, asynchronous rearrangement, as supported by Tantillo’s hypothesis.23,24 Tantillo’s investigation into the cationic rearrangement reactions of terpene natural products using theoretical calculations often show that these rearrangements are not stepwise, but rather occur in a concerted manner.24 For example, the proposed biosynthesis of presilphiperfolanol (2.67) involves a 1,2-alkyl shift/alkene cyclisation of 2.64 to presilphiperfolanyl cation (2.66) (Scheme 2.13).25 Tantillo’s calculations suggested the secondary carbocation 2.65 was not involved in the biosynthesis, but rather a 1,2-shift and alkene cyclization of 2.64 occurred simultaneously to give 2.67 via a single transition state.23 We have also consulted Tantillo on the biosynthesis of hyperjaponol C (2.54), and he predicted that it is likely to occur in a concerted, asynchronous rearrangement.

H OH H H 1,2-alkyl H alkene H H 1,3-hydride shift/ shift cyclization H2O

H 2.64 2.65 2.66 2.67: (–)-presilphiperfolanol

asynchronous, concerted rearrangment

Scheme 2.13: Proposed biosynthesis of (–)-presilphiperfolanol (2.67).23,25

16 2.2. Results and discussion 2.2.1. Synthesis of norflavesone (2.58)

HO OH HO OH i-PrCOCl, AlCl3 PhNO2, 65 °C 87% OH OH O 2.68: phloroglucinol 2.57 Scheme 2.14: Acylation of phloroglucinol (2.68).

The synthesis began with the Friedel-Crafts acylation of phloroglucinol (2.68) using AlCl3 and i- 26 PrCOCl in PhNO2 at 65 ºC, the reaction worked smoothly and can be scaled up to 10 g (Scheme 2.14). We have also lowered the amount of isobutyryl chloride from 2 equiv. to 1.2 equiv. without any loss of yield.

HO OH MeI, KOt-Bu HO O MeOH, reflux 72% OH O OH O 2.69 2.70 Scheme 2.15: Dearomative trimethylation reported by Nguyen.27

HO OH MeI, KOt-Bu, HO O HO OH HO O MeOH, 65 °C

79% OH O OH O OH O OH O

2.57 2.58: norflavesone 2.71 not observed Scheme 2.16: Synthesis of norflavesone (2.58).

Nguyen and coworkers27 have reported a dearomative trimethylation on 2.69 using KOt-Bu and MeI (Scheme 2.15), which was applied to acylphloroglucinol 2.57 and afforded norflavesone (2.58) in good yield (Scheme 2.16). We also investigated whether using fewer equivalents of base and MeI could give dimethylated acylphloroglucinol 2.71. Interestingly, we did not observe 2.71, but a lower yield of trimethylated acylphloroglucinol 2.58. We hypothesize after the first methylation of 2.57, the reactivity of the molecule increases until the third methylation has completed. This observation was different from the prenylation of acylphloroglucinol 2.57 reported by George, where he observed a mixture of diprenylated 2.72/2.73 and triprenylated acylphloroglucinol 2.74 (Scheme 2.17).28

17 HO OH prenyl bromide, KOt-Bu MeOH, 65 °C HO OH HO O + HO O +

OH O OH O OH O OH O 2.57 2.72 2.73 2.74 39% 30% 10% Scheme 2.17: Dearomative prenylation reported by George28.

2.2.2. Biomimetic total synthesis of hyperjapones B (2.50) & D (2.52) In the biomimetic total synthesis of hyperguinone B (2.77) reported by George, 2.75 was oxidized by PhI(OAc)2 and TEMPO to give a heterodiene intermediate 2.76, which underwent a 6π electocyclization to give hyperguinone B (2.77) (Scheme 2.18). We hoped that in a similar fashion, norflavesone (2.58) could be oxidized to give the heterodiene intermediate 2.59, then undergoes a hetero-Diels-Alder reaction with humulene (2.11) or caryophyllene (2.30).

PhI(OAc) , TEMPO, THF HO O 2 −78 °C to rt O O 6π electrocyclization O O

OH O OH O OH O 2.75 2.76 2.77: hyperguinone B 73% Scheme 2.18: Biomimetic total synthesis of hyperguinone B (2.77) by George28.

To our delight, reaction with caryophyllene (2.30) and norflavesone (2.58) in the presence of

PhI(OAc)2 and TEMPO gave a 2.5:1 mixture of hyperjapones B (2.50) and D (2.52) in 26% overall yield (Scheme 2.19). The ratio of hyperjapones B and D was in good agreement with the population of conformers in caryophyllene (2.30), where the predominant βα and αα conformers reacted with the heterodiene intermediate 2.59 to give hyperjapone B (2.50), while the less abundant ββ conformer gave hyperjapone D (2.52).19 We found that the mixture of hyperjapones B and D were impossible to separate by flash column chromatography or HPLC. Interestingly, we observed the hyperjapones B (2.50) and D (2.52) mixture was not soluble in most organic solvents, where hyperjapone B (2.50) could be selectively recrystallized from MeOH. Unfortunately, the filtrate still contained a 1:1 mixture of hyperjapones B (2.50) and D (2.52). We have attempted to recrystallise the hyperjapones B (2.50) and D (2.52) mixture with various other solvents, but to no avail. At this point, we did not pursue further on the purification of hyperjapone D (2.52). The optical rotation of !" !" hyperjapone B (2.50) is [!]! +10º (c 0.62, MeOH), which matches with the natural product [!]! +5º (c 0.15, MeOH), and hence confirmed the absolute configuration of hyperjapone B (2.50). 18

caryophyllene (2.30) H H HO O PhI(OAc)2, TEMPO O O O O THF, –78 °C to rt + 26%, d.r. 2.5:1 2.50/2.52 H H H H OH O OH O OH O 2.58: norflavesone 2.50: hyperjapone B 2.52: hyperjapone D Scheme 2.19: Biomimetic total synthesis of hyperjapones B (2.50) and D (2.52).

2.2.3. Investigation on the hetero-Diels-Alder reaction We then further investigated the oxidation of norflavesone (2.58) by screening different conditions in an attempt to improve the yield for the oxidative cycloaddition (Table 2.1). First, we discovered the reaction did not proceed at –78 °C to –40 °C, and the starting material would decompose if the reaction started at room temperature. It suggests that the heterodiene 2.59 would be formed between –40 °C and room temperature. We also performed a few control experiments to show that a stoichiometric amount of TEMPO is essential for this oxidation. We have also attempted to improve the reaction by screening various co-oxidants. For instance, Ag2O has been used as an oxidant to generate an o-quinone methide 2.79 in the total synthesis of schefflone (2.80) (Scheme 2.20).29

From the collective results, we found that the combination of Ag2O and TEMPO gave the highest overall yield of 60%.

OMe OMe

OMe hetero-Diels-Alder Ag2O, benzene, rt MeO OMe reaction MeO OMe O O OMe O O OMe OH O OMe OMe OMe O MeO OMe 2.78 2.80: schefflone 2.79 72%

Scheme 2.20: Biomimetic total synthesis of schefflone (2.80) using Ag2O as an oxidant by Lei.29

19 Table 2.1: Conditions screened for the oxidative hetero-Diels-Alder reaction

H HO O H H caryophyllene (2.30) O O O O + d.r. 2.5:1 2.50/2.52 H H OH O H H OH O OH O 2.58: norflavesone 2.50: hyperjapone B 2.52: hyperjapone D caryophyllene combined yield (2.30) oxidant(s) solvent conditions of 2.50/2.52 (no of equiv.)

2 DDQ (3 equiv.) PhMe rt, 1 h decomposition 1.2 DDQ (1.1 equiv.) PhMe −78 °C to rt, 16 h decomposition

2 PDC (1.2 equiv.) CH2Cl2 −78 °C to rt decomposition

2 MnO2 (4 equiv.) Et2O −78 °C to rt, 16 h decomposition

2 K3Fe(CN)6 (2 equiv.) MeCN/H2O 0 °C to rt, 16 h decomposition 2 CAN (1.2 equiv.) MeOH 0 °C, 1 h decomposition

2 Ag2O (1.2 equiv.) benzene rt, 4 h decomposition

2 PhI(OAc)2 (1.2 equiv.) THF −78 °C to rt, 4 h decomposition 2 IBX (1.5 equiv.) MeCN −40 °C to rt, 16 h 20% PhI(OAc) (1.1 equiv.), TEMPO 2 2 THF −78 °C to rt, 4 h 26% (2 equiv.) PhI(CF COO) (1.1 equiv.), 2 3 2 THF −78 °C to rt, 5 h 26% TEMPO (2 equiv.) PhI(OAc) (1.1 equiv.), TEMPO 2 2 THF rt, 1 h decomposition (2 equiv.) PhI(OAc) (1.1 equiv.), TEMPO 1.2 2 THF −78 °C to rt, 4 h 26% (2 equiv.) PhI(OAc) (1.1 equiv.), TEMPO 1.2 2 THF −78 °C to −40 °C, 2 h no reaction (2 equiv.) PhI(OAc) (1.1 equiv.), TEMPO 1.2 2 THF −78 °C to 60 °C, 4 h 26% (1.2 equiv.)

PhI(OAc)2 (1.1 equiv.), TEMPO 32% 1.2 Et2O −78 °C to rt, 4 h (1.2 equiv.) CAN (1.2 equiv.), TEMPO (1.2 2 MeOH −78 °C to rt 4 h 39% equiv.) Ag O (1.1 equiv.), TEMPO (1.2 1.2 2 Et O −78 °C to rt, 16 h 60% equiv.) 2 Ag O (1.1 equiv.), TEMPO (0.4 2 2 Et O −78 °C to rt, 16 h 40% equiv.) 2 Ag O (1.1 equiv.), TEMPO (0.2 2 2 Et O −78 °C to rt, 16 h 15% equiv.) 2

2 TEMPO (2 equiv.) Et2O −78 °C to rt, 2 d 40%

20 Here, we proposed two possible oxidation pathways for the formation of heterodiene 2.59 (Scheme 2.21). The first pathway involves a single electron oxidation of TEMPO to a reactive species 2.81, which then reacts with norflavesone (2.58) via a hydride transfer to give heterodiene 2.59. The second pathway suggests norflavesone (2.58) undergoing a single electron oxidation by TEMPO to give a radical intermediate 2.82, which then further oxidized to heterodiene 2.59. From the control experiment where 2 equiv. of TEMPO was used for the oxidative hetero-Diels-Alder reaction, and 40% yield of hyperjapones B (2.50) and D (2.52) was obtained, we propose the second oxidation pathway is more plausible.

Proposed mechanism 1:

O O O O [O] H + + N N N O O OH H OH O OH O TEMPO 2.81 2.58: norflavesone 2.59 TEMPO-H Proposed mechanism 2:

N HO O O O O O O TEMPO [O] e.g. Ag O, OH O 2 OH O PhI(OAc)2, OH O 2.58: norflavesone 2.82 CAN, 2.59 TEMPO

N OH TEMPO-H Scheme 2.21: Proposed oxidation mechanism of norflavesone (2.58) by TEMPO.

21 2.2.4. Biomimetic total synthesis of hyperjapone A (2.49)

2 5 1

8 9

humulene (2.11) HO O TEMPO, Ag2O O O THF, −78 °C to rt 32% H OH O OH O 2.58 (±)-2.49: hyperjapone A Scheme 2.22: Biomimetic total synthesis of hyperjapone A (2.49).

With the optimized conditions, we moved to the total synthesis of hyperjapone A (2.49). By changing the dienophile to humulene (2.11), the oxidative hetero-Diels-Alder reaction afforded hyperjapone A (2.49) in 32% yield (Scheme 2.22). The yield was almost halved from the reaction with caryophyllene (2.30). This was expected as the Δ4,5-alkene in caryophyllene (2.30) is more reactive than the Δ1,2-alkene in humulene (2.11). For example, caryophyllene (2.30) can be oxidized by air readily while humulene (2.11) cannot.13 Nonetheless, the hetero-Diels-Alder reaction was chemoselective and regioselective as we did not 4,5 8,9 observe any reaction on the Δ and Δ -alkenes. The reaction was also diastereoselective, where the relative stereochemistry was pre-determined by the Z-configuration of the Δ1,2-alkene of humulene (2.11). We then investigated whether it was possible for a second hetero-Diels-Alder reaction to take place on the Δ8,9-alkene by reducing the equivalents of humulene (2.11), as shown in the biomimetic total synthesis of lucidene (2.27) by Baldwin.11,12 However, we observed hyperjapone A (2.49) was the only product. We have also heated the reaction in a sealed tube, but no second Diels-Alder reaction was observed.

2.2.5. Biomimetic total synthesis of hyperjaponol C (2.56) With hyperjapone A (2.49) in hand, we moved onto the total synthesis of hyperjaponols A to C. Treating hyperjapone A (2.49) with m-CPBA in standard conditions gave epoxide 2.60 (Scheme 2.23). The epoxidation was chemoselective, as there was no epoxidation on the Δ4,5-alkene. A similar observation was reported in the diepoxidation on humulene (2.11) by Fujita.8

22 HMBC HMBC

O O m-CPBA O O O OH CH2Cl2, 0 °C 20 O 76% O O H H H OH O OH O O 20 (±)-2.49: hyperjapone A 2.60 2.60a Scheme 2.23: Epoxidation of hyperjapone A (2.49).

13 Interestingly, we observed a minor isomer in the C NMR of epoxide 2.60 in d6-acetone, which we hypothesized to be the tautomer of epoxide 2.60a. Note that we did not observe any tautomer in the

NMR spectra of hyperjapone A (2.49) or hyperjapone B (2.50) in d6-acetone. To investigate whether the minor product in epoxide 2.60 is a tautomer or a diastereoisomer, we performed NMR studies on the same epoxide sample in different solvents, and compared the ratio of the heptet (H-20) around 4 ppm (Figure 2.6). The most distinctive results were from d6-acetone and CDCl3, where the ratio of the two isomers was 10:1 in d6-acetone and 4:1 in CDCl3. With this piece of information, we concluded the minor isomer observed in the NMR spectra was in fact a tautomer.

1 1 epoxide 2.60, H NMR (500 MHz, d6-acetone) epoxide 2.60, H NMR (500 MHz, CDCl3) 10:1 isomers 4:1 isomers

1 1 epoxide 2.60, H NMR (500 MHz, d6-DMSO) epoxide 2.60, H NMR (500 MHz, C6D6) 20:1 isomers (poor solubility) 7:1 isomers 1 Figure 2.6: H NMR spectra of epoxide 2.60 in d6-acetone, CDCl3, d6-DMSO and C6D6.

23 We then focused on the acid-catalysed rearrangement of the epoxide 2.60 to hyperjaponols A to C.

We first tried p-TsOH in CH2Cl2 at room temperature, which gave hyperjaponol C (2.56) in 43% yield, presumably derived from the cationic alkene-cyclization/1,2-alkyl shift cascade reaction (Scheme 2.24). The reaction could also be done with catalytic p-TsOH (0.1 equiv.) with no loss of yield.

HMBC HMBC H H O O p-TsOH·H2O O O O OH CH2Cl2, rt O O 43% HO HO H H H OH O OH O O 2.60 (±)-2.56: hyperjaponol C 2.56a Scheme 2.24: Biomimetic total synthesis of hyperjaponol C (2.56).

In the acid-catalysed rearrangement reaction, we observed impurities that shared similar Rf to hyperjaponol C (2.56), which could not be separated by column chromatography. We read a 30,31 purification modification of column chromatography involving doping AgNO3 with SiO2, which is an underutilized trick that is used more often in natural product isolation than in organic synthesis. It is believed that the Ag+ can interact with the π electrons in alkenes, which differentiates organic molecules with varied alkene systems and thus providing a secondary interaction in silica.30,31 This modified purification worked perfectly and we obtained pure hyperjaponol C (2.56) in 43% yield (Figure 2.7).

1 Figure 2.7: H NMR spectra of hyperjaponol C (2.56) (500 MHz, CDCl3). a) (purified with

SiO2), b) (purified with AgNO3 doped SiO2).

Similar to the epoxide 2.60, a tautomer of hyperjaponol C (2.56) was also observed in the NMR spectra, with a ratio of 10:1 in d6-acetone and 5:1 in CDCl3 respectively. To further investigate the acid-catalysed rearrangement reaction, we screened a series of protic acids and Lewis acids (Table

2.2). We discovered treating epoxide 2.60 with concentrated H2SO4 in acetone/H2O under reflux gave hyperjaponol C (2.56) in 8% yield, while BF3·OEt2 gave hyperjaponol C (2.56) in 16% yield.

Other Lewis acids (e.g. TiCl4, SnCl2) led to decomposition.

2.2.6. Biomimetic total synthesis of hyperjaponol A (2.54)

O O O OH O O (NC)2C=C(CN)2 LiBr, acetone, 50 °C O O 59% H HO H HO H OH O OH O O 2.60 (±)-2.54: hyperjaponol A 2.54a Scheme 2.25: Biomimetic total synthesis of hyperjaponol A (2.54).

We then investigated the use of (NC)2C=C(CN)2 for the ring opening reaction of epoxide 2.60, as it has been used in a similar reaction with caryophyllene oxide (2.31) reported by Marcias-Sanchez.15 We were delighted to observe hyperjaponol A (2.54) in 59% yield in this reaction (Scheme 2.25). We believed hyperjaponol B (2.55) could be generated from similar conditions. Our hypothesis was the formation of the endocyclic alkene would be favoured under thermal conditions. However, when a higher boiling point solvent pent-2-one was used, it gave hyperjaponol A (2.54) in a lower yield (42%) and other solvents led to decomposition (Table 2.2). Unfortunately, we have yet to observe hyperjaponol B (2.55) in our synthetic work.

Table 2.2: Conditions screened for the acid-catalysed rearrangement reaction

O O H O O conditions O O or

O HO H HO H OH O H OH O OH O 2.60 (±)-2.54: hyperjaponol A 2.56: hyperjaponol C

reagents solvent conditions product, yield

(NC) C=C(CN) (0.2 2 2 acetone rt no reaction equiv.), LiBr (5 equiv.) (NC) C=C(CN) (0.2 hyperjaponol A (2.54), 2 2 acetone 50 °C, 2 h equiv.), LiBr (5 equiv.) 59% (NC) C=C(CN) (0.2 hyperjaponol A (2.54), 2 2 pentan-2-one reflux, 2.5 h equiv.), LiBr (5 equiv.) 42% (NC) C=C(CN) (0.2 2 2 PhMe reflux, 1 d decomposition equiv.), LiBr (5 equiv.) (NC) C=C(CN) (0.2 2 2 EtOH reflux, 4 h decomposition equiv.), LiBr (5 equiv.) (NC) C=C(CN) (0.2 2 2 CH Cl rt, 2 d no reaction equiv.), LiBr (5 equiv.) 2 2 (NC) C=C(CN) (0.1 2 2 DMSO rt, 16 h no reaction equiv.) (NC) C=C(CN) (0.1 2 2 DMSO reflux, 16 h decomposition equiv.)

1 M HCl CHCl3 rt, 2 h no reaction

1 M HCl CHCl3 reflux, 3 h no reaction hyperjaponol A (2.54), conc. HCl CHCl rt, 3 h 3 30%

conc. HCl CHCl3 reflux, 2 h hyperjaponol A (2.54),

26 30%

H2SO4 acetone/H2O, 9:1 reflux, 3 h hyperjaponol C (2.56), 8%

H2SO4 acetone/H2O, 9:1 rt, 1 d no reaction

TFA CH2Cl2 –20 °C, 2 h hyperjaponol C (2.56), 7% hyperjaponol C (2.56), p-TsOH·H O (1 equiv.) CH Cl –20 °C, 3 h 2 2 2 30% hyperjaponol C (2.56), p-TsOH·H O (1 equiv.) CH Cl 0 °C to rt, 2 h 2 2 2 43% p-TsOH·H2O (1 equiv.) CHCl3 0 °C to rt, 4 h no reaction hyperjaponol C (2.56), p-TsOH·H O (1 equiv.) acetone 50 °C, 1 d 2 20% hyperjaponol C (2.56), p-TsOH·H O (0.1 equiv.) CH Cl rt, 3 h 2 2 2 37% p-TsOH·H2O (0.1 equiv.) MeOH/H2O 1:1 60 °C, 4 h no reaction

CSA (1 equiv.) CH2Cl2 0 °C, 2 h no reaction hyperjaponol C (2.56), CSA (1 equiv.) CH Cl rt, 1 d 2 2 30% sodium formate formic acid rt, 1 h decomposition sodium acetate acetic acid rt, 2 d no reaction

BF3·OEt2 (1 equiv.) CH2Cl2 –78 °C no reaction –78 °C to –20 hyperjaponol C (2.56), BF ·OEt (1 equiv.) CH Cl 3 2 2 2 °C, 6 h 16%

TiCl4 (1 equiv.) CH2Cl2 0 °C, 30 min decomposition

SnCl2 (1 equiv.) CH2Cl2 0 °C, 30 min decomposition

27 In the synthesis of hyperjaponol C (2.56), both epoxidation and acid-catalysed rearrangement reactions were robust and clean, so it was natural to attempt a one pot reaction.32 Indeed, the reaction went extraordinarily well. After the addition of m-CPBA to hyperjapone A (2.49), the reaction was monitored by TLC carefully; when all of the hyperjapone A (2.49) was consumed, catalytic p-TsOH was added. The reaction went to completion overnight and gave 33% yield of hyperjaponol C (2.56), which was approximately the combined yield of the two separate steps (Scheme 2.26). Alternatively, m-CPBA and p-TsOH could be added simultaneously to hyperjapone

A (2.49) in CH2Cl2 and gave hyperjaponol C (2.56) in 26% yield.

m-CPBA, CH2Cl2 0 °C then H O O p-TsOH·H2O, rt O O 33% or HO H H OH O m-CPBA, p-TsOH·H2O OH O (±)-2.49: hyperjapone A CH2Cl2 rt 26% (±)-2.56: hyperjaponol C Scheme 2.26: One pot epoxidation and acid-catalysed rearrangement reaction of hyperjapone A (2.49) to give hyperjaponol C (2.56).

2.2.7. Biomimetic total synthesis of hyperjapones C (2.51) and E (2.53)

HO OH (S)-EtCH(Me)COCl, AlCl3 HO OH MeI, KOt-Bu HO O PhNO2, 65 °C H MeOH, 65 °C H 71% 69% OH OH O OH O 2.68: phloroglucinol 2.83 2.84: norisoleptospermone Scheme 2.27: Total synthesis of norisoleptospermone (2.84).

After the total synthesis of hyperjaponols A (2.54) and C (2.56), we moved onto the synthesis of hyperjapones C (2.51) and E (2.53). The synthesis started from Friedel-Crafts acylation of 33 phloroglucinol (2.68) with AlCl3 and (S)-EtCH(Me)COCl. The reaction went smoothly and gave acylphloroglucinol 2.83 in good yield. Trimethylation of acylphloroglucinol 2.83 by KOt-Bu and MeI gave norisoleptospermone (2.84) in 69% yield (Scheme 2.27), which is also a natural product isolated from a flowering plant Lepsospermum scoparium.22

28 H

caryophyllene (2.30) H H HO O TEMPO, Ag2O O O O O H THF, –78 °C to rt H H + 61%, d.r. 2.5:1 2.51/2.53 H H H H OH O OH O OH O 2.84: norisoleptospermone 2.51: hyperjapone C 2.53: hyperjapone E Scheme 2.28: Biomimetic total synthesis of hyperjapones C (2.51) and E (2.53).

With norisoleptospermone (2.84) in hand, we proceeded to the oxidative hetero-Diels-Alder reaction with caryophyllene (2.30). Under the optimized conditions, the reaction gave a 2.5:1 mixture of hyperjapones C (2.51) and E (2.53) in 61% yield (Scheme 2.28). We could not separate the two isomers by flash column chromatography or HPLC.

humulene (2.11) HO O TEMPO, Ag2O H THF, –78 °C to rt O O O O H + H 35%, d.r. 1:1 2.85/2.86 OH O H H OH O OH O 2.84: norisoleptospermone 2.85 2.86

undiscovered natural products? Scheme 2.29: Biomimetic total synthesis of hyperjapones analogues 2.85 and 2.86.

Since we believe the biosynthesis of hyperjapones A-E is highly predisposed and non-enzymatic, the hyperjapone analogues 2.85 and 2.86 derived from norisoleptospermone (2.84) and humulene

(2.11) could be two undiscovered natural products. The addition of TEMPO and Ag2O to noisoleptospermone (2.84) and humulene (2.11) in THF gave a 1:1 mixture of 2.85 and 2.86 with 35% overall yield (Scheme 2.29).

29 2.2.8. Isolation of hyperjapones F to I (2.87–2.90)

O O O O O O O O

H OH O OH O OH O OH O 2.87: (–)-hyperjapone F 2.88: (+)-hyperjapone G 2.89: (+)-hyperjapone H 2.90: (+)-hyperjapone I *absolute configurations of hyperjapones H (2.89) and I (2.90) were not determined from isolation hetero-Diels-Alder reaction

O O H + (+)-2.92: (+)-(β)-pinene (+)-2.93: (+)-(α)-pinene

OH O

2.59 2.91: (–)-sabinene (–)-2.92: (–)-(β)-pinene (–)-2.93: (–)-(α)-pinene Figure 2.8: Structures of hyperjapones F to I (2.87–2.90).

After we published our work on the total synthesis of hyperjapones and hyperjaponols,34 the isolation of hyperjapones F-I (2.87–2.90) was reported by Xu (Figure 2.8).35 These natural products were also isolated from Hypericum japonicum, and they are presumably biosynthesized from the hetero-Diels-Alder reaction with 2.59. Note the absolute configurations of hyperjapones H (2.89) and I (2.90) were not determined from the isolation. Therefore, we aimed to synthesize both enantiomers of hyperjapones H (2.89) and I (2.90) and determine the absolute configuration of the natural products.

2.2.9. Biomimetic total synthesis of hyperjapones F and G (2.87 & 2.88)

(−)-sabinene (2.91) HO O Ag2O, TEMPO O O O O THF, −78 °C to rt + 13% OH O OH O OH O 2.58: norflavesone 2.87: hyperjapone F 2.88: hyperjapone G 1:1 Scheme 2.30: Biomimetic Total synthesis of hyperjapones F (2.87) and G (2.88).

Similar to our previous synthesis of hyperjapones, norflavesone (2.58) was oxidised and reacted with (–)-sabinene (2.91) to give a 1:1 mixture of hyperjapones F (2.87) and G (2.88) (Scheme 2.30).

30 The yield of this reaction was only 13%, as the terminal alkene of (–)-sabinene (2.91) is less reactive compared to the strained trans-alkenes of caryophyllene (2.30) and humulene (2.11).

2.2.10. Biomimetic total synthesis of hyperjapone H (2.89)

(+)-(β)-pinene (+)-2.92 (−)-(β)-pinene (−)-2.92 CAN, TEMPO HO O CAN, TEMPO O O MeOH, −78 ºC to rt MeOH, −78 °C to rt O O 25% 27% OH O OH O OH O (+)-2.89: (+)-hyperjapone H 2.58: norflavesone (−)-2.89: (−)-hyperjapone H Scheme 2.31: Biomimetic total synthesis of hyperjapone H (2.89).

Interestingly, the oxidative hetero-Diels-Alder reaction did not proceed as well with (β)-pinene

(2.92) using Ag2O and TEMPO. The reaction gave hyperjapone H (2.89) as well as some complex side products, which were difficult to separate by column chromatography. The AgNO3 doped SiO2 column chromatography did not work on this occasion. Looking back at the Table 2.1, we repeated the reaction using our second-best conditions with CAN and TEMPO in MeOH. To our delight, treating (+)-(β)-pinene (+)-2.92 and norflavesone (2.58) with CAN and TEMPO gave a 25% yield of (+)-hyperjapone H (+)-2.89; while using (–)-(β)-pinene (–)-2.92 gave a 27% yield of (−)- !" hyperjapone H (−)-2.89 (Scheme 2.31). The optical rotations of (+)-2.89 and (−)-2.89 are [!]! !" +24º (c 1.0, MeOH) and [!]! −20° (c 1.0, MeOH). The natural sample has an optical rotation of !" [!]! +3° (c 0.12, MeOH). Since the racemic (β)-pinene (2.92) is naturally occurring, we suspect that natural hyperjapone H (2.92) is a racemate, if not a scalemic mixture.

2.2.11. Biomimetic total synthesis of hyperjapone I (2.90)

(+)-(α)-pinene (+)-2.93 (−)-(α)-pinene (−)-2.93 O O CAN, TEMPO HO O CAN, TEMPO O O MeOH, −78 ºC to rt MeOH, −78 ºC to rt 8% 5% H H OH O OH O OH O (+)-2.90: (+)-hyperjapone I 2.58: norflavesone (−)-2.90: (−)-hyperjapone I Scheme 2.32: Biomimetic total synthesis of hyperjapone I (2.90).

31 In the synthesis of hyperajapone I (2.90), we again observed inseparable side products using Ag2O and TEMPO, and hence we chose to use CAN and TEMPO for the reaction. The yield was 8% with (+)-(α)-pinene (+)-2.93 and 5% with (–)-(α)-pinene (+)-2.93 (Scheme 2.32). The yield of this reaction was relatively low, due to the poor reactivity of the tri-substituted alkene in (α)-pinene !" !" (2.93). The optical rotations are [!]! = +95° (c 1.0, MeOH) for (+)-2.90 and [!]! = −98° (c 1.0, !" MeOH) for (−)-2.90. The natural product has an optical rotation of [!]! = +51° (c 0.13, MeOH). Therefore, we suspect that natural hyperjapone I (2.90) is possibly a scalemic mixture, or the natural sample might be impure. We also managed to recrystallise hyperjapone I (2.90) from MeOH and obtained an X-ray structure to confirm the relative stereochemistry (Figure 2.9).

Figure 2.9: X-ray structure of hyperjapone I (2.90).

2.2.12. Preliminary theoretical calculations of the transition state of cationic alkene- cyclization/1,2-shift To investigate the concerted, asynchronous cationic alkene-cyclization/1,2-alkyl shift hypothesis, we performed calculations on each proposed carbocation intermediate and their corresponding transition states. From the diagram (Figure 2.10), the energy of the first carbocation 2.61 is the highest, and the energy of the final carbocation 2.63 is the lowest. It suggests the overall reaction profile is enthalpically favoured. On the left of the diagram, it represents the asynchronous cation-alkene cyclization/1,2-alkyl shift, where 2.61 rearranges to 2.63 in a single transition state. On the right side of the diagram, it illustrates the stepwise process: the alkene-cyclization of 2.61 gives 2.62, followed by 1,2-alkyl shift to give 2.63. The calculation shows that the asynchronous cation-alkene cyclization/1,2-alkyl shift is a reasonable pathway. In the transition state 2.61–2.63, the distance between C-4 and C-9 is 1.71 Å (from 3.85 Å in 2.61), which shows partial single bond character (1.54 Å for a C-C single bond).

32 And the double bond between C-4 and C-5 is elongated to 1.41 Å (from 1.33 Å in 2.61). And the ring is slightly twisted, which is in position for the 1,2-alkyl shift. However, the calculation for the stepwise process is problematic. First, in the optimised structure of 2.62, the distance between C-4 to C-9 is 1.84 Å, which is slightly longer than a single bond, suggesting it is unlikely for 2.62 to have a 6/7 membered ring structure. In addition, the transition state from 2.61 to 2.62 could not be calculated. Moreover, in the transition state 2.62–2.63, the distance between C-4 and C-9 is elongated to 2.02 Å, which suggests the single bond between C-4 and C-9 is broken. Therefore, it is not a simple 1,2-alkyl shift to reach 2.63 from 2.62. To conclude, our calculations agreed with Tantillo’s hypothesis, suggesting the concerted, asynchronous process is favoured over the stepwise process.23,24

no transition from 2.61 to 2.62 transition state 2.62-2.63 transitin state 2.61-2.63

-1 +116.13 kJ mol-1 +146.95 kJ mol

5 4 O O 9 H O O HO 9 4 H OH O 2.61 HO H OH O -1 –32.66 kJ mol 2.62

–209.48 kJ mol-1 –207.64 kJ mol-1

H O O

HO H OH O 2.63 Figure 2.10: Energy diagram of the carbocation rearrangements. All ground states were calculated from 6-31G+(d,p), with Density Functional Theory m062x. The transition states were calculated from 6-31+G(d), with Density Functional Theory m062x.

33 2.3. Summary We have developed a concise biomimetic total synthesis of hyperjapones A-I via an oxidative hetero-Diels-Alder reaction. We have also converted hyperjapone A into hyperjaponol C via an epoxidation and an acid-catalysed rearrangement cascade reaction, which generated 2 rings, and 4 stereocenters in 1 step. The overall synthesis is protecting group free with good pot economy (Figure 2.11).36,37 It is also noteworthy that the total synthesis mirrored our biosynthetic proposal precisely. The synthesis of hyperjaponol C highlights the reactivity of all 3 alkenes in humulene, where each alkene is reacted sequentially in a chemoselective, stereoselective and regioselective manner: hetero-Diels-Alder reaction on the Δ1,2-alkene, epoxidation on the Δ8,9-alkene and the acid- catalysed rearrangement on the Δ4,5-alkene. The synthesis suggests a highly predisposed biosynthesis of hyperjaponol C.

4 steps H 7% overall yield O O HO OH HO 6 C-C bonds H O 6 stereocentres OH O 3 rings MeI Cl (±)-2.56: hyperjaponol C

Figure 2.11: Summary of the biomimetic total synthesis of hyperjaponol C (2.56).

The syntheses of hyperjapones B, H and I confirmed the absolute configuration of these natural products. We plan to distribute both enantiomers of hyperjapones H and I, epoxide 2.60 and hyperjapones analogues 2.85/2.86 to the isolation chemists. We hope the synthesis of hyperjapones and hyperjaponols could help identify and characterise natural products that are yet to be isolated. After our publication on the synthesis of hyperjapones and hyperjaponols, there were a few reports on the isolation and biomimetic total synthesis of structurally related natural products.38,39,40 These natural products were synthesized via a hetero-Diels-Alder reaction with caryophyllene or humulene (Figure 2.12).

34 H H O OMe O OMe O OMe H ∗ H ∗ H H O O H O *S, 2.94: frutescone B *S, 2.96: frutescone E 2.98: (±)-frutescone G *R, 2.95: frutescone C *R, 2.97: frutescone F

OH H H H O O OH H H ∗ O H O O H O O O O O O O

*S, 2.101: rhodomyrtial A 2.99: rhodomentone A 2.100: rhodomentone B *R, 2.102: rhodomyrtial B Figure 2.12: Isolation and synthesis of frutescones by Wang38, rhodomentones A and B by Qiu39 and rhodomyrtials A and B by Luo and Kong40.

35 2.4. References 1. Clayden, J.; Greeves, N.; Warren, S. G., Organic chemistry. Oxford University Press: Oxford; New York, 2012. 2. Nicolaou, K. C.; Snyder, S. A.; Montagnon, T.; Vassilikogiannakis, G. Angew. Chem. Int. Ed., 2002, 41, 1668. 3. Snyder, S. A.; Kontes, F. Isr. J. Chem., 2011, 51, 378. 4. Nicolaou, K. C.; Snyder, S. A. Proceedings of the National Academy of Sciences of the United States of America, 2004, 101, 11929. 5. Smith, A. B.; Sestelo, J. P.; Dormer, P. G. J. Am. Chem. Soc., 1995, 117, 10755. 6. Kuttruff, C. A.; Zipse, H.; Trauner, D. Angew. Chem. Int. Ed., 2011, 50, 1402. 7. Heravi, M. M.; Ahmadi, T.; Ghavidel, M.; Heidari, B.; Hamidi, H. RSC Adv., 2015, 5, 101999. 8. Zigon, N.; Hoshino, M.; Yoshioka, S.; Inokuma, Y.; Fujita, M. Angew. Chem. Int. Ed., 2015, 54, 9033. 9. Bryson, I.; Roberts, J. S.; Sattar, A. Tetrahedron Lett., 1980, 21, 201. 10. Gao, Y.; Wang, G. Q.; Wei, K.; Hai, P.; Wang, F.; Liu, J. K. Org. Lett., 2012, 14, 5936. 11. Adlington, R. M.; Baldwin, J. E.; Pritchard, G. J.; Williams, A. J.; Watkin, D. J. Org. Lett., 1999, 1, 1937. 12. Rodriguez, R.; Moses, J. E.; Adlington, R. M.; Baldwin, J. E. Org. Biomol. Chem., 2005, 3, 3488. 13. Steenackers, B.; Campagnol, N.; Fransaer, J.; Hermans, I.; De Vos, D. Chem. Eur. J., 2015, 21, 2146. 14. Barrero, A. F.; Herrador, M. M.; del Moral, J. F. Q.; Arteaga, P.; Sanchez, E. M.; Arteaga, J. F.; Piedra, M. Eur. J. Org. Chem., 2006, 3434. 15. Collado, I. G.; Hanson, J. R.; MaciasSanchez, A. J. Tetrahedron, 1996, 52, 7961. 16. Spence, J. T. J.; George, J. H. Org. Lett., 2011, 13, 5318. 17. Takao, K.; Noguchi, S.; Sakamoto, S.; Kimura, M.; Yoshida, K.; Tadano, K. J. Am. Chem. Soc., 2015, 137, 15971. 18. Lawrence, A. L.; Adlington, R. M.; Baldwin, J. E.; Lee, V.; Kershaw, J. A.; Thompson, A. L. Org. Lett., 2010, 12, 1676. 19. Clericuzio, M.; Alagona, G.; Ghio, C.; Toma, L. J. Org. Chem., 2000, 65, 6910. 20. Yang, X. W.; Li, Y. P.; Su, J.; Ma, W. G.; Xu, G. Org. Lett., 2016, 18, 1876. 21. Hu, L. Z.; Zhang, Y.; Zhu, H. C.; Liu, J. J.; Li, H.; Li, X. N.; Sun, W. G.; Zeng, J. F.; Xue, Y. B.; Zhang, Y. H. Org. Lett., 2016, 18, 2272. 22. Killeen, D. P.; Larsen, L.; Dayan, F. E.; Gordon, K. C.; Perry, N. B.; van Klink, J. W. J. Nat. Prod., 2016, 79, 564. 23. Tantillo, D. J. Chem. Soc. Rev., 2010, 39, 2847. 24. Tantillo, D. J. Nat. Prod. Rep., 2011, 28, 1035. 25. Hong, A. Y.; Stoltz, B. M. Angew. Chem. Int. Ed., 2014, 53, 5248. 26. Crombie, L.; Jones, R. C. F.; Palmer, C. J. J. Chem. Soc., Perkins Trans. 1, 1987, 317. 27. Nguyen, N. T.; Pham, V. C.; Litaudon, M.; Gueritte, F.; Bodo, B.; Nguyen, V. T.; Nguyen, V. H. Tetrahedron, 2009, 65, 7171. 28. George, J. H.; Hesse, M. D.; Baldwin, J. E.; Adlington, R. M. Org. Lett., 2010, 12, 3532. 29. Liao, D. H.; Li, H. H.; Lei, X. G. Org. Lett., 2012, 14, 18. 30. Mander, L. N.; Williams, C. M. Tetrahedron, 2016, 72, 1133. 31. Williams, C. M.; Mander, L. N. Tetrahedron, 2001, 57, 425. 32. Markwell-Heys, A. W.; Kuan, K. K. W.; George, J. H. Org. Lett., 2015, 17, 4228. 33. Fobofou, S. A. T.; Franke, K.; Porzel, A.; Brandt, W.; Wessjohann, L. A. J. Nat. Prod., 2016, 79, 743.

36 34. Lam, H. C.; Spence, J. T. J.; George, J. H. Angew. Chem. Int. Ed., 2016, 55, 10368. 35. Li, Y. P.; Yang, X. W.; Xia, F.; Yan, H.; Ma, W. G.; Xu, G. Tetrahedron Lett., 2016, 57, 5868. 36. Gaich, T.; Baran, P. S. J. Org. Chem., 2010, 75, 4657. 37. Hayashi, Y. Chem. Sci., 2016, 7, 866. 38. Hou, J. Q.; Guo, C.; Zhao, J. J.; He, Q. W.; Zhang, B. B.; Wang, H. J. Org. Chem., 2017, 82, 1448. 39. Liu, H. X.; Chen, K.; Yuan, Y.; Xu, Z. F.; Tan, H. B.; Qiu, S. X. Org. Biomol. Chem., 2016, 14, 7354. 40. Zhang, Y. L.; Chen, C.; Wang, X. B.; Wu, L.; Yang, M. H.; Luo, J.; Zhang, C.; Sun, H. B.; Luo, J. G.; Kong, L. Y. Org. Lett., 2016, 18, 4068.

37 2.5. Experimental 2.5.1. General methods

All chemicals used were purchased from commercial suppliers and used as received. All reactions were performed under an inert atmosphere of N2. All organic extracts were dried over anhydrous magnesium sulfate. Thin layer chromatography was performed using aluminium sheets coated with silica gel F254. Visualization was aided by viewing under a UV lamp and staining with ceric ammonium molybdate or KMnO4 stain followed by heating. All Rf values were measured to the nearest 0.05. Flash chromatography was performed using 40-63 micron grade silica gel. Melting points were recorded on a digital melting point apparatus and are uncorrected. Infrared spectra were recorded using an FT-IR spectrometer as the neat compounds. High field NMR was recorded using 1 13 a 500 MHz spectrometer ( H at 500 MHz, C at 125 MHz). Solvents used for spectra were d6- 1 acetone or CDCl3 unless otherwise specified. H chemical shifts are reported in ppm on the δ-scale 13 relative to TMS (δ 0.0) or CDCl3 (δ 7.26) and C NMR are reported in ppm relative to CDCl3 (δ 77.00). Multiplicities are reported as (br) broad, (s) singlet, (d) doublet, (t) triplet, (q) quartet, (quin) quintet, (sext) sextet, (hept) heptet and (m) multiplet. All J-values were rounded to the nearest 0.1 Hz. ESI high resolution mass spectra were recorded on a ESI-TOF mass spectrometer. Optical rotations were measured on a modular circular polarimeter.

38 2.5.2. Experimental procedures

HO OH HO OH i-PrCOCl, AlCl3 PhNO2, 65 °C 87% OH OH O 2.68: phloroglucinol 2.57

To a solution of phloroglucinol (2.68) (5.0 g, 39.6 mmol) in PhNO2 (50 mL) at room temperature was added AlCl3 (21.2 g, 159 mmol) portionwise, followed by slow addition of isopropyl chloride (4.59 mL, 43.6 mmol). The mixture was heated at 65 ºC for 3.5 h. The solution was cooled to room temperature, then quenched with 1 M HCl (30 mL) and diluted with MeOH (10 mL). The mixture was extracted with EtOAc (2 × 50 mL). The combined organic layers were extracted with 1 M NaOH (2 × 50 mL). The aqueous extracts were acidified by conc. HCl. The aqueous layer was extracted with EtOAc (3 × 70 mL). The combined organic extracts were washed with brine (200 mL), dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (4:1 → 2:1, petrol/EtOAc gradient elution) to give 2.57 as a yellow solid (6.75 g, 87%). Data for 2.57 matched that of the published data.1

Rf = 0.45 (1:1, petrol/EtOAc)

1 H NMR (500 MHz, CD3OD): δ 5.81 (s, 1H), 3.97 (hept, J = 6.7 Hz, 1H), 1.13 (d, J = 6.8 Hz, 6H).

13 C NMR (125 MHZ, CD3OD): δ 211.6, 165.82, 165.75, 104.6, 95.8, 39.9, 19.7.

39 HO OH MeI, KOt-Bu HO O MeOH, 65 °C

79% OH O OH O 2.57 2.58: norflavesone To a solution of 2.57 (2.84 g, 14.4 mmol) in MeOH (30 mL) at room temperature was added KOt- Bu (6.00 g, 53.6 mmol) and MeI (2.69 mL, 43.2 mmol). The solution was heated at 65 °C for 3 h. The reaction was cooled to room temperature, then acidified by 1 M aqueous HCl solution (40 mL). The aqueous solution was extracted with EtOAc (2 × 30 mL). The combined organic extracts were washed with brine, dried over MgSO4, filtered, and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (4:1, petrol/EtOAc) to give norflavesone 2.58 as a white gum (2.61 g, 79%). Data for 2.58 matched that of the isolation data.2

Rf = 0.40 (1:1, petrol/EtOAc) IR (neat): 3171, 2981, 2929, 1643, 1575, 1514, 1462, 1376, 1334, 1223, 1181, 1165 cm-1.

1 H NMR (500 MHz, d6-DMSO): δ 19.13 (br s, 1H), 3.90 (hept, J = 6.8 Hz, 1H), 1.78 (s, 3H), 1.29 (s, 6H), 1.04 (d, J = 6.8 Hz, 6H).

13 C NMR (125 MHz, d6-DMSO): δ 206.5, 195.8, 189.1, 176.1, 103.5, 101.8, 48.5, 34.6, 24.3, 18.9, 7.4.

- HRMS (ESI): calculated for C13H17O4 237.1132 [M−H] , found 237.1135.

40 humulene (2.11) HO O TEMPO, Ag2O O O THF, −78 °C to rt

32% H OH O OH O 2.58 (±)-2.49: hyperjapone A

To a solution of 2.58 (1.80 g, mmol), and α-humulene (2.11) (1.24 g, 6.07 mmol) in Et2O (30 mL) at −78 °C was added Ag2O (1.97 g, 6.49 mmol) and TEMPO (1.42 g, 9.10 mmol). The reaction was stirred at −78 °C for 1 h, then warmed to room temperature and stirred for 16 h. The solution was filtered and concentrated in vacuo. The residue was purified by flash column chromatography on

SiO2 (1:0 → 30:1, petrol/EtOAc gradient elution) to give (±)-hyperjapone A (2.49) as a white solid (860 mg, 32%).

Mp: 174 – 175 °C

Rf = 0.65 (5:1, petrol/EtOAc) IR (neat): 2968, 2934, 2861, 1656, 1619, 1509, 1473, 1381, 1265, 1190, 1158, 1103 cm-1.

1 H NMR (500 MHz, d6-acetone): δ 19.26 (br s, 1H), 5.23 (d, J = 15.7 Hz, 1H), 5.11 (dd, J = 12.0, 3.2 Hz, 1H), 5.04 (ddd, J = 15.9, 10.5, 2.7 Hz, 1H), 3.98 (hept, J = 6.8 Hz, 1H), 2.78 (m, 1H), 2.56 (d, J = 14.6 Hz, 1H), 2.46 (dd, J = 14.7, 10.6 Hz, 1H), 2.24 (d, J = 12.5 Hz, 1H), 2.12 (dd, J = 12.7, 7.2 Hz, 1H), 1.92 (t, J = 12.2 Hz, 1H), 1.85 – 1.83 (m, 2H), 1.75 (dd, J = 13.0, 4.5 Hz, 1H), 1.65 (s, 3H), 1.45 – 1.40 (m, 1H), 1.35 (s, 3H), 1.29 (s, 3H), 1.25 – 1.20 (m, 1H), 1.17 (s, 3H), 1.11 (d, J = 6.0 Hz, 3H), 1.09 (d, J = 5.6 Hz, 3H), 1.05 (s, 3H), 1.03 (s, 3H).

13 C NMR (125 MHz, d6-acetone): δ 207.9, 196.7, 189.4, 173.7, 143.8, 137.4, 123.8, 120.7, 103.1, 85.9, 48.9, 42.6, 42.2, 38.8, 38.3, 35.8, 35.6, 30.6, 30.4, 25.2, 24.4, 24.2, 22.5, 20.3, 19.4, 19.2, 17.2.

+ HRMS (ESI): calculated for C28H41O4 441.2999 [M+H] , found 441.3000.

41 O O m-CPBA O O O OH CH2Cl2, 0 °C O 76% O O H H H OH O OH O O (±)-2.49: hyperjapone A 2.60 2.60a

To a solution of (±)-hyperjapone A (2.49) (474 mg, 1.08 mmol) in CH2Cl2 (20 mL) at 0 °C was added m-CPBA (77%, 265 mg, 1.18 mmol). The reaction was stirred at 0 °C for 1 h, then quenched with saturated aqueous NaHCO3 solution. The organic layer was separated and the aqueous layer was extracted with CH2Cl2 (2 × 20 mL). The combined organic extracts were washed with brine (50 mL), dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (4:1, petrol/EtOAc) to give epoxide 2.60 as a white solid (493 mg, 76%).

Mp: 220 – 223 °C

Rf = 0.20 (10:1, petrol/EtOAc) IR (neat): 2958, 2933, 2871, 1703, 1658, 1623, 1517, 1473, 1380, 1316, 1237, 1195 cm-1.

10:1 mixture of tautomers in d6-acetone

Data for major tautomer 2.60:

1 H NMR (500 MHz, d6-acetone): δ 19.23 (s, 1H), 5.53 (dd, J = 15.7, 1.2 Hz, 1H), 5.32 (ddd, J = 15.7, 10.1, 4.0 Hz, 1H), 3.97 (hept, J = 6.7 Hz, 1H), 2.73 (d, J = 10.9 Hz, 1H), 2.69 (d, J = 10.8 Hz, 1H), 2.65 – 2.60 (m, 2H), 2.13 (dd, J = 13.6, 9.0 Hz, 1H), 1.81 – 1.75 (m, 2H), 1.70 (d, J = 13.6 Hz, 1H), 1.62 (dd, J = 14.4, 9.9 Hz, 1H), 1.36 (s, 3H), 1.32 – 1.30 (m, 1H), 1.29 (s, 3H), 1.29 (s, 3H), 1.25 – 1.23 (m, 1H), 1.19 (s, 3H), 1.17 (s, 3H), 1.10 (d, J = 5.2 Hz, 3H), 1.09 (d, J = 5.2 Hz, 3H), 1.04 (s, 3H), 0.99 (dd, J = 13.6, 9.9 Hz, 1H).

13 C NMR (125 MHz, d6-acetone): δ 207.9, 196.7, 189.4, 173.7, 142.1, 121.2, 105.1, 103.3, 84.6, 61.9, 60.7, 84.9, 42.8, 41.1, 38.3, 37.6, 36.2, 35.7, 31.3, 26.2, 25.4, 24.4, 24.2, 22.3, 19.8, 19.4, 19.2, 17.6.

42 Partial data for minor tautomer 2.60a:

1 H NMR (500 MHz, d6-acetone): δ 5.51 (d, J = 11.3 Hz, 1H), 4.24 (hept, J = 6.6 Hz, 1H).

13 C NMR (125 MHz, d6-acetone): δ 205.8, 199.4 183.1, 166.0, 142.8, 121.5, 108.6, 103.1, 82.7, 61.9, 60.8, 49.0, 42.9, 41.1, 38.3, 37.7, 36.5, 36.2, 30.6, 26.4, 25.3, 24.4, 24.2, 23.2, 19.6, 19.34, 19.29, 17.6.

4:1 mixture of tautomers in CDCl3

Data for major tautomer 2.60:

1 H NMR (500 MHz, CDCl3): δ 19.14 (s, 1H), 5.39 (d, J = 15.7 Hz, 1H), 5.23 – 5.18 (m, 1H), 3.97 (hept, J = 6.3 Hz, 1H), 2.73 (dd, J = 16.6, 4.8 Hz, 1H), 2.65 – 2.62 (m, 2H), 2.43 (dd, J = 14.0, 10.9 Hz, 1H), 2.18 (dd, J = 13.4, 9.4 Hz, 1H), 1.82 – 1.78 (m, 2H), 1.75 – 1.67 (m, 1H), 1.60 (td, J = 11.7, 4.7 Hz, 1H), 1.49 – 1.43 (m, 2H), 1.38 (s, 3H), 1.32 (s, 3H), 1.29 (s, 3H), 1.16 (s, 3H), 1.15 (d, J = 7.9 Hz, 3H), 1.14 (d, J = 5.8 Hz, 3H), 1.11 (s, 3H), 1.05 (s, 3H), 1.03 – 0.99 (m, 1H).

13 C NMR (125 MHz, CDCl3): δ 207.8, 196.7, 188.6, 172.6, 142.5, 120.2, 104.7, 102.5, 83.3, 61.8, 60.9, 48.4, 42.5, 40.3, 37.6, 36.9, 35.7, 35.5, 30.9, 25.7, 25.3, 24.2, 23.9, 21.8, 19.7, 19.2, 19.0, 17.4.

Partial data for minor tautomer 2.60a:

13 C NMR (125 MHz, CDCl3): δ 210.5, 198.6, 183.4, 165.9, 142.2, 120.5, 107.9, 107.8, 81.8, 61.9, 60.9, 43.3, 42.6, 40.3, 37.7, 36.9, 36.3, 35.7, 30.9, 25.9, 25.2, 24.3, 24.2, 22.5, 19.5, 19.2, 19.1, 17.5.

+ HRMS (ESI): calculated for C28H41O5 457.2949 [M+H] , found 457.2946.

43 H H O O p-TsOH·H2O O O O OH CH2Cl2, rt O O HO HO H 43% H H OH O OH O O 2.60 (±)-2.56: hyperjaponol C 2.56a

To a solution of 2.60 (82 mg, 0.18 mmol) in CH2Cl2 (3 mL) at room temperature was added p-

TsOH·H2O (38 mg, 0.20 mmol) and stirred for 1 h. The reaction was quenched with saturated aqueous NaHCO3 solution. The organic layer was separated and the aqueous layer was extracted with CH2Cl2 (2 × 5 mL). The combined organic extracts were washed with brine, dried over

MgSO4, filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (doped with 10% w/w AgNO3, 3:1, petrol/EtOAc) to give (±)- hyperjaponol C (2.56) as a white solid (35 mg, 43%). Mp: 161 – 163 °C.

Rf = 0.75 (1:1, petrol/EtOAc) IR (neat): 3448, 2973, 2930, 2869, 1649, 1612, 1570, 1523, 1472, 1451, 1380, 1165 cm-1.

5:1 mixture of tautomers in CDCl3 Data for major tautomer 2.56:

1 H NMR (500 MHz, CDCl3): δ 19.08 (s, 1H), 4.77 (s, 1H), 4.73 (s, 1H), 3.96 (hept, J = 6.8 Hz, 1H), 3.73 (t, J = 9.1 Hz, 1H), 2.45 (dd, J = 16.5, 4.9 Hz, 1H), 2.26 (td, J = 11.2, 5.6 Hz, 1H), 2.05 (dd, J = 17.4, 14.3 Hz, 1H), 2.00 (d, J = 16.5 Hz, 1H), 1.95 – 1.85 (m, 3H), 1.83 – 1.80 (m, 1H), 1.74 (dd, J = 10.2, 6.0 Hz, 1H), 1.72 – 1.70 (m, 1H), 1.67 (s, 3H), 1.61 (br s, 1H), 1.52 – 1.41 (m, 2H), 1.30 (s, 3H), 1.28 – 1.27 (m, 1H), 1.26 (s, 3H), 1.15 (d, J = 6.8 Hz, 3H), 1.13 (d, J = 5.9 Hz, 3H), 1.12 (s, 3H), 0.82 (s, 3H).

13 C NMR (125 MHz, CDCl3): δ 208.0, 197.1, 188.6, 173.7, 146.0, 111.1, 104.7, 103.6, 84.3, 82.3, 48.5, 47.0, 46.9, 41.4, 41.3, 40.6, 39.3, 36.0, 35.6, 26.2, 25.8, 24.7, 23.4, 20.4, 19.5, 19.14, 19.11, 12.3.

44 Data for minor tautomer 2.56a: (partially characterised)

1 H NMR (500 MHz, CDCl3): δ 18.56 (br s, 1H), 4.21 (hept, J = 6.8 Hz, 1H).

13 C NMR (125 MHz, CDCl3): δ 210.5, 198.8, 183.7, 166.9, 146.2, 111.0, 104.7, 103.6, 82.8, 82.3, 48.5, 47.2, 46.9, 43.3, 41.3, 40.8, 39.3, 36.3, 36.0, 26.3, 25.6, 25.5, 23.8, 20.2, 19.5, 19.2, 19.1, 13.4.

+ HRMS (ESI): calculated for C28H41O5 457.2949 [M+H] , found 457.2948.

10:1 mixture of tautomers in d6-acetone Data for major tautomer 2.56:

1 H NMR (500 MHz, d6-acetone): δ 19.19 (s, 1H), 4.75 (s, 2H), 3.95 (hept, J = 7.0 Hz, 1H), 3.75 (br s, 1H), 3.73 – 3.71 (m, 1H), 2.42 (dd, J = 16.3, 4.9 Hz, 1H), 2.30 (td, J = 11.5, 5.7 Hz, 1H), 2.07 – 2.05 (overlapped m, 2H), 1.97 – 1.93 (m, 2H), 1.91 – 1.85 (m, 2H), 1.84 – 1.78 (m, 2H), 1.69 (s, 3H), 1.53 – 1.48 (m, 2H), 1.35 – 1.32 (m, 1H), 1.27 (s, 3H), 1.24 (s, 3H), 1.19 (s, 3H), 1.10 (d, J = 7.4 Hz, 3H), 1.08 (d, J = 8.6 Hz, 3H), 0.84 (s, 3H).

13 C NMR (125 MHz, d6-acetone): δ 208.1, 196.8, 189.4, 174.6, 147.6, 111.0, 105.0, 104.3, 85.4, 82.1, 49.0, 48.0, 47.6, 42.0, 41.2, 40.0, 36.6, 35.8, 26.8, 25.9, 25.3, 23.7, 20.5, 19.5, 19.30, 19.28, 12.6.

45 m-CPBA, CH2Cl2 H H O O 0 °C then O O O OH p-TsOH·H2O, rt HO HO O H 33% H H OH O OH O O (±)-2.49: hyperjapone A (±)-2.56: hyperjaponol C 2.56a

To a solution of of (±)-hyperjapone A (2.49) (220 mg, 0.50 mmol) in CH2Cl2 (20 mL) at 0 °C was added m-CPBA (77%, 123 mg, 0.55 mmol). The reaction was stirred at 0 °C for 1 h. p-TsOH·H2O (105 mg, 0.55 mmol) was added. The reaction was warmed to room temperature and stirred for 1 h, then quenched with saturated aqueous NaHCO3 solution. The organic layer was separated and the aqueous layer was extracted with CH2Cl2 (2 × 20 mL). The combined organic extracts were washed with brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (doped with 10% AgNO3, 3:1, petrol/EtOAc) to give (±)- hyperjaponol C (2.56) as a white solid (75 mg, 33%).

O O (NC)2C=C(CN)2 O O O OH LiBr, acetone, 50 °C O O 59% H HO H HO H OH O OH O O 2.60 (±)-2.54: hyperjaponol A 2.54a To a solution of 2.60 (22 mg, 0.048 mmol) in acetone (3 mL) at room temperature was added tetracyanoethylene (1 mg, 9.6 µmol) and LiBr (21 mg, 0.24 mmol). The solution was heated at 50

°C for 2 h. The reaction was quenched with H2O (5 mL). The aqueous layer was extracted with

Et2O (4 × 10 mL). The combined organic extracts were washed with brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by flash column chromatography on

SiO2 (2:1, petrol/EtOAc) to give (±)-hyperjaponol A (2.54) as a colourless oil (13 mg, 59%). Data for 2.54:

Rf = 0.70 (petrol/EtOAc, 1:1, petrol/EtOAc) IR (neat): 3448, 2956, 2933, 2869, 1731, 1655, 1619, 1595, 1534, 1473, 1382, 1349, 1309 cm-1.

5:1 mixture of tautomers in CDCl3 Data for major tautomer 2.54:

1 H NMR (500 MHz, CDCl3): δ 19.16 (s, 1H), 5.39 (d, J = 15.7 Hz, 1H), 5.21 (s, 1H), 5.16 (ddd, J = 15.4, 9.9, 4.0 Hz, 1H), 4.96 (s, 1H), 3.97 (hept, J = 6.6 Hz, 1H), 3.89 (d, J = 9.0 Hz, 1H), 2.83 (d, J = 11.6 Hz, 1H), 2.52 (dd, J = 13.8, 3.9 Hz, 1H), 2.48 (dd, J = 13.2, 8.6 Hz, 1H), 2.39 (dd, J = 14.1, 10.0 Hz, 1H), 2.12 (dd, J =13.7, 9.7 Hz, 1H), 2.05 (dd, J = 13.4, 10.1 Hz, 1H), 1.85 – 1.79 (m, 2H), 1.64 – 1.60 (m, 2H), 1.40 – 1.39 (m, 1H), 1.37 (s, 3H), 1.31 (s, 3H), 1.17 (d, J = 8.1 Hz, 3H), 1.15 (d, J = 7.0 Hz, 3H), 1.11 (s, 3H), 1.09 (s, 3H), 1.04 (s, 3H).

13 C NMR (125 MHz, CDCl3): δ 207.9, 196.9, 188.6, 172.8, 155.5, 144.4, 120.0, 113.7, 104.7, 102.5, 83.8, 72.9, 49.0, 48.2, 43.7, 37.4, 35.9, 35.5, 32.7, 32.1, 30.6, 25.3, 24.6, 24.1, 22.1, 19.5, 19.2, 19.1.

Data for minor tautomer 2.54a: (partially characterised)

1 H NMR (500 MHz, CDCl3): δ 18.59 (s, 1H), 5.37 (d, J = 15.7 Hz, 1H), 5.19 (s, 1H), 4.95 (s, 1H), 4.23 (hept, J = 6.71 Hz, 1H).

13 C NMR (12t MHz, CDCl3): δ 210.5, 198.7, 183.6, 166.0, 155.8, 144.1, 120.4, 113.6, 107.8, 102.6, 82.3, 72.8, 49.0, 43.7, 43.3, 47.6, 36.3, 36.0, 32.7, 30.6, 29.9, 25.2, 24.6, 24.3, 22.8, 19.5, 9.29, 19.25.

+ HRMS (ESI): calculated for C28H41O5 457.2949 [M+H] , found 457.2947. 47 H H O O

H H H caryophyllene (2.30) OH O HO O TEMPO, Ag2O 2.50: hyperjapone B THF, –78 °C to rt + 60%, d.r. 2.5:1 2.50/2.52 H OH O O O 2.58 H H OH O 2.52: hyperjapone D

To a solution of 2.58 (350 mg, 1.47 mmol) and caryophyllene (2.30) (0.66 mL, 2.94 mmol) in Et2O

(10 mL) at −78 °C was added Ag2O (209 mg, 1.76 mmol) and TEMPO (459 mg, 2.94 mmol). The mixture was stirred for −78 °C for 1 h, then warmed to room temperature over 30 min and stirred at room temperature for 16 h. The solution was filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (1:0 → 30:1, petrol/EtOAc gradient elution) to give hyperjapones B (2.50) and D (2.52) as a yellow gum (388 mg, 60%, d.r. 2.5:1). A small sample of hyperjapones B (2.50) and D (2.52) was recrystallized from MeOH to give hyperjapone B (2.50) as white crystals.

Mp = 140 − 142 °C

Rf = 0.40 (1:1, petrol/EtOAc) Data for hyperjapone B (2.50): IR (neat): 2930, 2870, 1659, 1627, 1519, 1472, 1380, 1368, 1321, 1275, 1245, 1199 cm-1.

!" [!]! = +10.2° (c 0.62, MeOH)

1 H NMR (500 MHz, d6-acetone): δ 19.23 (br s, 1H), 4.92 (s, 1H), 4.90 (s, 1H), 3.97 (hept, J = 6.8 Hz, 1H), 2.54 – 2.46 (m, 2H), 2.38 (dd, J = 16.5, 5.1 Hz, 1H), 2.27 – 2.17 (m, 2H), 2.08 – 2.03 (overlapped m, 1H), 1.98 – 1.92 (m, 3H), 1.83 – 1.76 (m, 2H), 1.73 (t, J = 10.4 Hz, 1H), 1.60 (dd, J = 10.5, 7.6 Hz, 1H), 1.57 – 1.45 (m, 2H), 1.32 (s, 3H), 1.28 (s, 3H), 1.20 (s, 3H), 1.10 (d, J = 5.4 Hz, 3H), 1.08 (d, J = 5.3 Hz, 3H), 1.01 (s, 3H), 0.97 (s, 3H).

13 C NMR (125 MHz, d6-acetone): δ 207.9, 196.7, 189.4, 173.6, 152.9, 110.7, 105.0, 102.9, 85.4, 54.0, 49.0, 42.8, 37.9, 37.1, 35.9, 35.8, 34.6, 34.2, 33.8, 30.4, 25.4, 25.3, 24.3, 23.4, 22.3, 21.2, 19.33, 19.26.

+ HRMS (ESI): calculated for C28H41O4 441.2999 [M+H] , found 441.2996.

48 Data for hyperjapone D (2.52):

1 H NMR (500 MHz, d6-acetone): δ 19.24 (br s, 1H), 4.84 (br s, 1H), 4.76 – 4.75 (m, 1H), 4.01 – 3.94 (overlapped m, 1H), 2.79 – 2.75 (overlapped m, 1H), 2.66 (dd, J = 16.5, 5.2 Hz, 1H), 2.54 – 2.46 (overlapped m, 1H), 2.27 – 2.11 (overlapped m, 3H), 1.91 – 1.87 (overlapped m, 1H), 1.84 – 1.74 (overlapped m, 1H), 1.73 – 1.68 (overlapped m, 2H), 1.62 – 1.55 (overlapped m, 3H), 1.53 – 1.46 (overlapped m, 2H), 1.33 (s, 3H), 1.27 (s, 3H), 1.13 (s, 3H), 1.11 – 1.08 (overlapped m, 6H), 1.00 (s, 3H), 0.98 (s, 3H).

13 C NMR (125 MHz, d6-acetone): δ 207.9, 196.7, 189.3, 173.9, 155.9, 110.3, 105.0, 102.9, 85.6, 57.2, 49.0, 43.0, 39.3, 37.3, 35.8, 35.2, 34.5, 34.2, 33.9, 29.9, 25.4, 24.2, 24.1, 23.3, 22.6, 20.1, 19.4, 19.2.

49 HO OH (S)-EtCH(Me)COCl, AlCl3 HO OH PhNO2, 65 °C H 71% OH OH O 2.68 2.83

To a solution of phloroglucinol (2.68) (0.95 g, 7.53 mmol) in PhNO2 (10 mL) at room temperature was added AlCl3 (4.02 g, 30.1 mmol) portionwise, followed by slow addition of (S)-methylbutyric acyl chloride (1.18 g, 9.79 mmol). The mixture was heated at 65 ºC for 16 h. The solution was cooled to room temperature, then quenched with 1 M HCl (10 mL) and diluted with MeOH (5 mL). The mixture was extracted with EtOAc (3 × 10 mL). The combined organic layers were extracted with 1 M NaOH (2 × 10 mL). The aqueous extracts were acidified by conc. HCl. The aqueous layer was extracted with EtOAc (3 × 30 mL). The combined organic extracts were washed with brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (4:1 → 2:1, petrol/EtOAc gradient elution) to give 2.83 as a yellow solid (1.11 g, 71%). Data for 2.83 matched that of the published data.3 Data for 2.83:

Rf = 0.65 (1:1, petrol/EtOAc)

!" [!]! = +26.8° (c 0.25, CHCl3)

1 H NMR (500 MHz, CD3OD): δ 6.05 (s, 2H), 4.10 (sext, J = 6.8 Hz, 1H), 2.06 (dp, J = 14.1, 7.2 Hz, 1H), 1.61 (dp, J = 14.5, 7.4 Hz, 1H), 1.36 (d, J = 6.7 Hz, 3H), 1.15 (t, J = 7.4 Hz, 3H).

13 C NMR (125 MHZ, CD3OD): δ 211.4, 165.84, 165.78, 105.2, 95.9, 46.7, 28.1, 17.1, 12.3.

50 MeI, KOt-Bu HO OH HO O H MeOH, 65 °C H 69% OH O OH O 2.83 2.84: norisoleptospermone To a solution of 2.83 (700 mg, 3.33 mmol) in MeOH (25 mL) at room temperature was added KOt- Bu (1.23 g, 10.99 mmol) and MeI (0.69 mL, 10.99 mmol). The reaction was stirred at 65 °C for 5 h, then cooled to room temperature. The reaction mixture was acidified with 1 M HCl (30 mL), then extracted with EtOAc (3 × 30 mL). The combined organic extracts were washed with brine, dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (4:1 → 2:1, petrol/EtOAc gradient elution) to give norisoleptosperone (2.84) as a yellow gum (580 mg, 69%). Data for 2.84 matched that of the isolation data.2

Data for 2.84:

Rf = 0.30 (1:1, petrol/EtOAc)

!" [!]! = +19.0° (c 0.87, CHCl3) IR (neat): 3229, 2969, 2934, 2876, 1648, 1583, 1518, 1473, 1378, 1228, 1180, 1164 cm-1.

1 H NMR (500 MHz, d6-DMSO): δ 19.21 (br s, 1H), 3.78 (sext, J = 6.8 Hz, 1H), 1.78 (s, 3H), 1.62 (sext, J = 7.2 Hz, 1H), 1.29 (overlapped m, 7H), 1.03 (d, J = 6.7 Hz, 3H), 0.83 (t, J = 7.4 Hz, 3H).

13 C NMR (125 MHz, d6-DMSO): δ 205.9, 195.9, 189.2, 175.8, 104.3, 101.9, 94.3, 48.5, 40.9, 26.2, 24.4, 24.0, 16.5, 11.7, 7.3.

+ HRMS (ESI): calculated for C14H21O4 253.1434 [M+H] , found 253.1431.

51 H H O O H H H H caryophyllene (2.30) OH O HO O H TEMPO, Ag2O 2.51: hyperjapone C THF, –78 °C to rt + 61%, d.r. 2.5:1 2.51/2.53 OH O H 2.84 O O H H H OH O 2.53: hyperjapone E

To a solution of 2.84 (118 mg, 0.40 mmol), and caryophyllene (2.30) (0.18 mL, 0.79 mmol) in Et2O

(5 mL) at −78 °C was added Ag2O (111 mg, 0.48 mmol) and TEMPO (123 mg, 0.79 mmol). The reaction was stirred at −78 °C for 1 h, then warmed to room temperature and stirred for 3 h. The solution was filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (1:0 → 50:1, petrol/EtOAc gradient elution) to give hyperjapones C (2.51) and E (2.53) as a yellow gum (129 mg, 61%, d.r. 2.5:1). Data for hyperjapone C (2.51):

Rf = 0.60 (5:1, petrol/EtOAc) IR (neat): 2952, 2930, 2870, 2659, 1627, 1519, 1472, 1380, 1368, 1199 cm-1.

1 H NMR (500 MHz, d6-acetone): δ 19.28 (s, 1H), 4.92 (s, 1H), 4.90 (s, 1H), 3.90 – 3.83 (overlapped m, 1H), 2.52 – 2.46 (overlapped m, 2H), 2.38 (dd, J = 16.5, 5.1 Hz, 1H), 2.27 – 2.16 (overlapped m, 2H), 2.27 – 2.16 (overlapped m, 2H), 2.05 (overlapped m, 1H), 1.99 – 1.92 (overlapped m, 1H), 1.86 – 1.68 (overlapped m, 4H), 1.60 (dd, J = 10.5, 7.6 Hz, 1H), 1.58 – 1.54 (overlapped m, 1H), 1.53 – 1.48 (overlapped m, 1H), 1.39 – 1.35 (overlapped m, 1H), 1.32 (s, 3H), 1.27 (s, 3H), 1.20 (s, 3H), 1.09 (d, J = 6.8 Hz, 3H), 1.01 (s, 3H), 0.97 (s, 3H), 0.87 (t, J = 7.4 Hz, 3H).

13 C NMR (125 MHz, d6-acetone): δ 207.2, 196.9, 189.4, 173.5, 152.9, 110.7, 105.9, 103.0, 85.4, 54.0, 49.1, 42.8, 42.2, 37.9, 37.1, 35.9, 34.7, 34.2, 33.8, 30.4, 27.4, 25.5, 25.3, 23.9, 23.4, 22.3, 21.2, 17.1, 12.2.

52 Data for hyperjapone E (2.53):

1 H NMR (500 MHz, d6-acetone): δ 19.31 (br s, 1H), 4.84 (s, 1H), 4.75 (t, J = 1.7 Hz, 1H), 3.90 – 3.83 (overlapped m, 1H), 2.80 – 2.78 (overlapped m, 1H), 2.67 (dd, J = 16.5, 5.2 Hz, 1H), 2.52 – 2.47 (overlapped m, 1H), 2.27 – 2.16 (overlapped m, 2H), 2.12 – 2.08 (m, 1H), 1.98 – 1.87 (overlapped m, 1H), 1.64 – 1.83 (overlapped m, 5H), 1.62 – 1.58 (overlapped m, 1H), 1.53 – 1.46 (overlapped m, 3H), 1.40 – 1.35 (m, 1H), 1.33 (s, 3H), 1.27 (s, 3H), 1.13 (s, 3H), 1.08 (d, J = 6.7 Hz, 3H), 1.00 (s, 3H), 0.98 (s, 3H), 0.91 – 0.88 (overlapped m, 3H).

13 C NMR (125MHz, d6-acetone): δ 207.3, 196.8, 189.4, 173.9, 156.0, 110.5, 105.9, 103.0, 85.6, 57.2, 49.0, 43.0, 42.1, 39.4, 39.3, 37.3, 35.2, 34.5, 33.9, 29.9, 27.5, 25.2, 24.4, 24.1, 23.3, 22.6, 20.1, 17.0, 12.2.

+ HRMS (ESI): calculated for C29H43O4 455.3156 [M+H] , found 455.3152.

53 O O H

H OH O 2.85 humulene (2.11) HO O + H TEMPO, Ag2O THF, –78 °C to rt O O 35%, d.r. 1:1 2.85/2.86 H OH O 2.84 H OH O 2.86

To a solution of 2.84 (93 mg, 0.39 mmol), and humulene (2.11) (160 mg, 0.78 mmol) in Et2O (5 mL) at −78 °C was added Ag2O (108 mg, 0.47 mmol) and TEMPO (122 mg, mmol). The reaction was stirred at −78 °C for 1 h, then warmed to room temperature and stirred for 16 h. The solution was filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (1:0 → 50:1, petrol/EtOAc gradient elution) to give a mixture of 2.85 and 2.86 as a white solid (59 mg, 35%, d.r. 1:1).

Rf = 0.60 (5:1, petrol/EtOAc) IR (neat): 2964, 2934, 2869, 1660, 1627, 1523, 1472, 1382, 1189. 1158 cm-1.

1 H NMR (500 MHz, d6-acetone): δ 19.32 (br s, 1H), 5.23 (d, J = 15.9 Hz, 1H), 5.13 – 5.11 (m, 1H), 5.05 (ddd, J = 15.9, 10.6, 2.6 Hz, 1H), 3.87 (pent, J = 6.7 Hz, 1H), 2.78 (s, 1H), 2.58 – 2.55 (m, 1H), 2.46 (dd, J = 14.6, 10.6 Hz, 1H), 2.24 (t, J = 2.26 Hz, 1H), 2.12 (dd, J = 12.7, 7.3 Hz, 1H), 1.93 – 1.88 (m, 1H), 1.84 – 1.80 (m, 2H), 1.76 – 1.69 (m, 2H), 1.65 (s, 3H), 1.45 – 1.38 (m, 2H), 1.35 (s, 3H), 1.29 (s, 3H), 1.23 – 1.20 (m, 1H), 1.17 (s, 3H), 1.09 (t, J = 6.7 Hz, 3H), 1.05 (s, 3H), 1.03 (s, 3H), 0.90 (t, J = 7.5 Hz, 3H).

13 C NMR (125 MHz, d6-acetone): δ 207.3, 196.8, 189.5, 173.7, 143.8, 137.4, 123.8, 120.7, 105.8, 103.2, 85.9, 49.0, 42.2, 42.1, 38.8, 38.3, 35.6, 30.4, 30.1, 29.9, 27.4, 24.9, 24.7, 24.2, 22.5, 20.3, 17.2, 17.0, 12.2.

+ HRMS (ESI): calculated for C29H43O4 455.3156 [M+H] , found 455.3153.

54 H

(−)-sabinene (2.91) HO O Ag2O, TEMPO O O O O THF, −78 ºC to rt + 13% OH O OH O OH O 2.58: norflavesone 2.87: hyperjapone F 2.88: hyperjapone G 1:1 To a solution of noflavesone (2.58) (200 mg, 0.84 mmol) and (−)-sabinene (2.91) (75%, 0.27 mL,

1.68 mmol) in anhydrous THF (10 mL) at −78 °C was added Ag2O (233 mg, 1.00 mmol) and TEMPO (157 mg, 1.00 mmol). The mixture was stirred at −78 °C for 1 h, then warmed to room temperature and stirred for an addition of 16 h. The reaction was filtered, then concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (100:1, petrol/EtOAc) to give a 1:1 mixture of hyperjapone F (2.87) and hyperjapone G (2.88) as a colourless oil (40 mg, 13%). Partial Data for 2.87 and 2.88:

Rf = 0.45 (20:1, petrol/EtOAc)

NMR data for hyperjapone F (2.87):

1 H NMR (500 MHz, d6-acetone): δ 3.97 (hept, J = 6.7 Hz, 1H), 2.54 – 2.43 (overlapped m, 1H), 2.34 – 2.27 (m, 1H), 2.00 – 1.93 (overlapped m, 1H), 1.90 – 1.84 (overlapped m, 2H), 1.79 – 1.72 (overlapped m, 1H), 1.66 (dd, J = 12.1, 8.1 Hz, 1H), 1.48 – 1.43 (overlapped m, 1H), 1.41 – 1.35 (overlapped m, 1H), 1.33 (s, 3H), 1.30 (s, 3H), 1.09 (d, J = 6.8 Hz, 6H), 1.03 (d, J = 6.9 Hz, 3H), 0.96 (overlapped d, J = 6.8 Hz, 3H), 0.54 (dd, J = 8.3, 5.5 Hz, 1H), 0.48 – 0.47 (overlapped m, 1H).

13 C NMR (125 MHz, d6-acetone): δ 208.0, 196.7, 189.6, 174.0, 105.1, 103.5, 49.2, 35.8, 35.3, 33.19, 33.15, 31.2, 28.3, 25.9, 25.5, 24.8, 20.4, 20.0, 19.32, 19.30, 17.2, 13.2.

NMR data for hyperjapone G (2.88):

1 H NMR (500 MHz, d6-acetone): δ 3.97 (hept, J = 6.7 Hz, 1H), 2.54 – 2.43 (overlapped m, 2H), 2.00 – 1.93 (overlapped m, 1H), 1.90 – 1.84 (overlapped m, 1H), 1.79 – 1.72 (overlapped m, 2H), 1.62 – 1.56 (m, 1H), 1.41 – 1.35 (overlapped m, 1H), 1.32 – 1.31 (m, 1H), 1.30 (s, 3H), 1.27 (s, 3H), 1.09 (d, J = 6.8 Hz, 6H), 0.96 (overlapped d, J = 6.9 Hz, 3H), 0.91 (d, J = 6.9 Hz, 3H), 0.90 – 0.88 (m, 1H), 0.48 – 0.47 (m, 1H).

13 C NMR (125 MHz, d6-acetone): δ 208.0, 196.7, 189.7, 175.2, 105.1, 103.2, 89.2, 49.2, 35.8, 34.4, 33.3, 30.0, 25.3, 25.2, 24.5, 19.83, 19.82, 19.32, 19.30, 16.3, 12.1.

+ HRMS (ESI): calculated for C23H33O4 373.2373 [M+H] , found 373.2375.

55 (+)-(β)-pinene (+)-2.92 HO O CAN, TEMPO O O MeOH, −78 ºC to rt 25% OH O OH O 2.58: norflavesone (+)-2.89: (+)-hyperjapone H To a solution of norflavesone (2.58) (200 mg, 0.84 mmol) and (+)-(β)-pinene (+)-2.92 (0.16 mL, 1.01 mmol) in MeOH (10 mL) at −78 °C was added ceric ammonium nitrate (552 mg, 1.01 mmol) and TEMPO (158 mmol, 1.01 mmol). The mixture was stirred at −78 °C for 10 min, then warmed to room temperature and stirred for 16 h. The reaction was diluted with H2O (10 mL), then extracted with Et2O (2 × 20 mL). The combined organic extracts were washed with H2O (40 mL), brine (40 mL), dried over MgSO4, filtered and concentrated in vacuo. The residue was partially purified by flash column chromatography on SiO2 (100:1 → 20:1 gradient elution, petrol/EtOAc).

The product was purified by flash column chromatography on SiO2 (1:1, petrol/CH2Cl2) to give (+)- hyperjapone H (+)-2.89 as a light yellow oil (78 mg, 25%). Data for (+)-2.89:

Rf = 0.35 (20:1, petrol/EtOAc) IR(neat): 2974, 2927, 2870, 1655, 1623, 1518, 1472, 1457, 1386, 1367, 1353, 1251, 1186 cm-1.

!" [!]! = +23.5° (c 1.0, MeOH) Data for major tautomer:

1 H NMR (500 MHz, d6-acetone): δ 19.21 (br s, 1H), 3.97 (hept, J = 6.8 Hz, 1H), 2.37 (t, J = 6.6 Hz, 2H), 2.31 – 2.26 (m, 1H), 2.16 (t, J = 5.1 Hz, 1H), 2.02 – 1.97 (m, 4H), 1.95 – 1.92 (m, 2H), 1.82 (dt, J = 13.8, 6.8 Hz, 1H), 1.67 (d, J = 10.2 Hz, 1H), 1.31 (s, 3H), 1.30 (s, 3H), 1.26 (s, 3H), 1.09 (d, J = 6.8 Hz, 6H), 1.04 (s, 3H).

13 C NMR (125 MHz, d6-acetone): δ 207.9, 196.7, 189.4, 174.0, 105.0, 103.2, 86.3, 50.4, 49.3, 41.4, 38.9, 35.8, 32.6, 29.1, 27.8, 27.0, 25.4, 25.0, 24.9, 23.4, 19.32, 19.30, 15.8.

Data for minor tautomer:

1 H NMR (500 MHz, d6-acetone): δ 18.60 (br s, 1H), 4.25 (hept, J = 6.8 Hz, 1H), 2.37 (t, J = 6.6 Hz, 2H), 2.31 – 2.26 (m, 1H), 2.11 (t, J = 5.1 Hz, 1H), 2.02 – 1.97 (m, 4H), 1.95 – 1.92 (m, 2H), 1.73 (td, J = 13.7, 7.0 Hz, 1H), 1.68 (d, J = 9.8 Hz, 1H), 1.45 (s, 3H), 1.40 (s, 3H), 1.31 (s, 3H), 1.30 (s, 3H), 1.26 (s, 3H), 1.12 (d, J = 7.0 Hz, 6H), 1.03 (s, 3H).

13 C NMR (125 MHz, d6-acetone): δ 210.9, 199.3, 183.2, 166.3, 108.7, 103.0, 84.3, 50.4, 41.5, 36.5, 35.9, 33.1, 30.6, 29.0, 27.9, 27.2, 25.5, 25.2, 25.1, 23.5, 16.5.

56 + HRMS (ESI): calculated for C23H33O4 373.2373 [M+H] , found 373.2372.

(−)-(β)-pinene (–)-2.92 HO O CAN, TEMPO O O MeOH, −78 ºC to rt 27% OH O OH O 2.58: norflavesone (−)-2.89: (−)-hyperjapone H To a solution of norflavesone (2.58) (200 mg, 0.84 mmol) and (−)-(β)-pinene (−)-2.92 (0.16 mL, 1.01 mmol) in MeOH (10 mL) at −78 °C was added ceric ammonium nitrate (552 mg, 1.01 mmol) and TEMPO (158 mmol, 1.01 mmol). The mixture was stirred at −78 °C for 10 min, then warmed to room temperature and stirred for 16 h. The reaction was diluted with H2O (10 mL), then extracted with Et2O (2 × 20 mL). The combined organic extracts were washed with H2O (40 mL), brine (40 mL), dried over MgSO4, filtered and concentrated in vacuo. The residue was partially purified by flash column chromatography on SiO2 (100:1→20:1 gradient elution, petrol/EtOAc).

The product was purified by flash column chromatography on SiO2 (1:1, petrol/CH2Cl2) to give (−)- hyperjapone H (−)-2.89 as a light yellow oil (83 mg, 27%).

Data for (−)-2.89:

Rf = 0.35 (20:1, petrol/EtOAc) IR(neat): 2972, 2929, 2871, 1656, 1624, 1523, 1474, 1387, 1312, 1252, 1193 cm-1.

!" [!]! = −19.7° (c 1.0, MeOH)

Data for major tautomer:

1 H NMR (500 MHz, d6-acetone): δ 19.21 (br s, 1H), 3.97 (hept, J = 6.8 Hz, 1H), 2.37 (t, J = 6.6 Hz, 2H), 2.31 – 2.26 (m, 1H), 2.16 (t, J = 5.1 Hz, 1H), 2.01 – 1.97 (m, 4H), 1.96 – 1.92 (m, 2H), 1.82 (dt, J = 13.8, 6.8 Hz, 1H), 1.67 (d, J = 10.2 Hz, 1H), 1.31 (s, 3H), 1.30 (s, 3H), 1.26 (s, 3H), 1.09 (d, J = 6.8 Hz, 6H), 1.04 (s, 3H).

13 C NMR (125 MHz, d6-acetone): δ 207.9, 196.7, 189.5, 174.0, 105.0, 103.2, 86.3, 50.4, 49.3, 41.4, 38.9, 35.8, 32.7, 29.1, 27.8, 27.0, 25.4, 25.0, 24.9, 23.4, 19.31, 19.29, 15.8.

Data for minor tautomer:

1 H NMR (500 MHz, d6-acetone): δ 18.60 (br s, 1H), 4.25 (hept, J = 6.8 Hz, 1H), 2.37 (t, J = 6.6 Hz, 2H), 2.31 – 2.26 (m, 1H), 2.11 (t, J = 5.1 Hz, 1H), 2.01 – 1.97 (m, 4H), 1.96 – 1.92 (m, 2H), 1.73 (td, J = 13.7, 7.0 Hz, 1H), 1.68 (d, J = 9.8 Hz, 1H), 1.45 (s, 3H), 1.40 (s, 3H), 1.31 (s, 3H), 1.30 (s, 3H), 1.26 (s, 3H), 1.12 (d, J = 7.0 Hz, 6H), 1.03 (s, 3H).

57 13 C NMR (125 MHz, d6-acetone): δ 210.9, 199.3, 183.2, 166.3, 108.7, 103.0, 84.3, 50.4, 41.5, 36.5, 35.9, 33.1, 30.6, 29.0, 27.9, 27.2, 25.5, 25.2, 25.1, 23.5, 16.5.

+ HRMS (ESI): calculated for C23H33O4 373.2373 [M+H] , found 373.2366.

58 (+)-(α)-pinene (+)-2.93 HO O CAN, TEMPO O O MeOH, −78 ºC to rt 8% H OH O OH O 2.58: norflavesone (+)-2.90: (+)-hyperjapone I To a solution of noflavesone (2.58) (1.00 g, 4.19 mmol) and (+)-(α)-pinene (+)-2.93 (1.33 mL, 8.38 mmol) in MeOH (50 mL) at −78 °C was added ceric ammonium nitrate (2.76 g, 5.03 mmol) and TEMPO (838 mg, 5.03 mmol). The mixture was stirred at −78 °C for 1 h, then warmed to room temperature and stirred for 2 d. The reaction was diluted with H2O (50 mL), then extracted with

Et2O (2 × 100 mL). The combined extracts were washed with H2O (100 mL), brine (100 mL), dried over MgSO4, filtered and concentrated in vacuo. The residue was purified by flash column chromatography on SiO2 (doped with 1% w/w AgNO3, 100:1, petrol/EtOAc) to give (+)- hyperjapone I (+)-2.90 as a white solid (130 mg, 8%). Data for (+)-2.90:

Rf = 0.35 (20:1, petrol/EtOAc)

M.p.: 110 – 111 °C

-1 IR(neat): 2972, 2922, 2873, 1650, 1617, 1516, 1472, 1439, 1388, 1343, 1317 cm .

!" [!]! = +95° (c 1.0, MeOH)

Data for major tautomer:

1 H NMR (500 MHz, d6-acetone): δ 19.31 (br s, 1H), 3.98 (hept, J = 6.8 Hz, 1H), 2.83 – 2.77 (m, 1H), 2.45 (dd, J = 16.2, 1.8 Hz, 1H), 2.39 (dd, J = 16.3, 6.8 Hz, 1H), 2.26 – 2.19 (m, 3H), 1.93 (dd, J = 9.6, 4.5 Hz, 1H), 1.43 (s, 3H), 1.37 – 1.32 (overlapped m, 1H), 1.33 (s, 3H), 1.29 (s, 3H), 1.28 (s, 3H), 1.15 (s, 3H), 1.11 (d, J = 6.8 Hz, 3H), 1.09 (d, J = 6.7 Hz, 3H), 0.92 – 0.88 (m, 1H).

13 C NMR (125 MHz, d6-acetone): δ 207.5, 196.6, 189.9, 174.8, 105.0, 100.4, 87.1, 55.1, 49.2, 41.8, 40.3, 35.8, 35.7, 31.2, 30.1, 28.9, 28.8, 26.2, 23.9, 23.2, 23.0, 19.6, 19.4, 19.3.

Data for minor tautomer:

1 H NMR (500 MHz, d6-acetone): δ 18.64 (br s, 1H), 4.27 (hept, J = 6.7 Hz, 1H), 2.73 (dd, J = 17.0, 7.8 Hz, 1H), 1.44 (s, 3H).

13 C NMR (125 MHz, d6-acetone): δ 210.7, 199.3, 183.2, 167.2, 105.7, 100.2, 84.9, 55.3, 49.2, 44.0, 36.5, 36.0, 31.7, 26.0, 24.3, 23.1, 20.4, 19.5.

+ HRMS (ESI): calculated for C23H33O4 373.2373 [M+H] , found 373.2379.

59 (−)-(α)-pinene (–)-2.93 HO O CAN, TEMPO O O MeOH, −78 ºC to rt 5% H OH O OH O 2.58: norflavesone (−)-2.90: (−)-hyperjapone I To a solution of norflavesone (2.58) (1.0 g, 4.19 mmol) and (−)-(α)-pinene (−)-2.93 (1.33 mL, 8.38 mmol) in MeOH (30 mL) at −78 °C was added ceric ammonium nitrate (2.76 g, 5.03 mmol) and TEMPO (828 mmol, 5.03 mmol). The mixture was stirred at −78 °C for 10 min, then warmed to room temperature and stirred for 5 d. The reaction was diluted with H2O (20 mL), then extracted with Et2O (2 × 50 mL). The combined organic extracts were washed with H2O (100 mL), brine (100 mL), dried over MgSO4, filtered and concentrated in vacuo. The residue was partially purified by flash column chromatography on SiO2 (100:1→50:1 gradient elution, petrol/EtOAc). The product was purified by flash column chromatography on SiO2 (doped with 1% w/w AgNO3, 100:1, petrol/EtOAc) to give (−)-hyperjapone I (−)-2.90 as a white solid (81 mg, 5%).

Data for (−)-2.90:

Rf = 0.35 (20:1, petrol/EtOAc)

M.p.: 111 – 113 °C IR (neat): 2980, 2923, 2869, 1650, 1619, 1514, 1471, 1441, 1388, 1343, 1318, 1251 cm-1.

!" [!]! = −98° (c 1.0, MeOH) Data for major tautomer:

1 H NMR (500 MHz, d6-acetone): δ 19.31 (br s, 1H), 3.97 (hept, J = 6.8 Hz, 1H), 2.83 – 2.78 (m, 1H), 2.45 (dd, J = 16,3m 1.9 Hz, 1H), 2.39 (dd, J = 16.2, 6.8 Hz, 1H), 2.26 – 2.19 (m, 3H), 1.94 – 1.91 (m, 1H), 1.43 (s, 3H), 1.36 – 1.34 (m, 1H), 1.33 (s, 3H), 1.29 (s, 3H), 1.28 (s, 3H), 1.15 (s, 3H), 1.11 (d, J = 6.8 Hz, 3H), 1.09 (d, J = 6.8 Hz, 3H), 0.92 – 0.88 (m, 1H).

13 C NMR (500 MHz, d6-acetone): δ 207.5, 196.6, 189.9, 174.8, 105.0, 100.3, 87.1, 55.1, 49.2, 41.8, 40.3, 35.8, 35.7, 31.2, 30.1, 28.9, 28.8, 26.2, 23.9, 23.0, 19.6, 19.4, 19.3.

Data for minor tautomer:

1 H NMR (500 MHz, d6-acetone): δ 18.64 (br s, 1H), 4.27 (hept, J = 6.8 Hz, 1H), 2.76 – 2.70 (m, 1H), 1.44 (s, 3H).

13 C NMR (500 MHz, d6-acetone): δ 210.7, 199.3, 183.2, 167.1, 105.7, 100.2, 84.9, 55.3, 49.2, 44.0, 36.5, 36.0, 31.7, 26.0, 24.3, 23.1, 20.4, 19.5.

+ HRMS (ESI): calculated for C23H33O4 373.2373 [M+H] , found 373.2379.

60 2.5.3. NMR spectra

HO OH

OH O 2.57

1H NMR 500 MHz

CD3OD

HO OH

OH O 2.57

13C NMR 125 MHz

CD3OD

HO O

OH O 2.58: norflavesone 1H NMR 500 MHz

d6-DMSO

HO O

OH O 2.58: norflavesone 1H NMR 500 MHz

d6-DMSO

62 HO O

OH O 2.58: norflavesone 13C NMR 125 MHz

d6-DMSO

63 O O

H OH O (±)-2.49: hyperjapone A 1H NMR 500 MHz

d6-acetone

O O

H OH O (±)-2.49: hyperjapone A 1H NMR 500 MHz

d6-acetone

64 O O

H OH O (±)-2.49: hyperjapone A 13C NMR 125 MHz

d6-acetone

65 O O

H OH O (±)-2.49: hyperjapone A COSY 500 MHz d6-acetone

O O

H OH O (±)-2.49: hyperjapone A HSQC 500 MHz d6-acetone

66 O O

H OH O (±)-2.49: hyperjapone A HMBC 500 MHz d6-acetone

O O

H OH O (±)-2.49: hyperjapone A NOESY 500 MHz d6-acetone

67 O O

H OH O (±)-2.49: hyperjapone A 1H NMR 500 MHz

CDCl3

O O

H OH O (±)-2.49: hyperjapone A 1H NMR 500 MHz

CDCl3

68 O O

H OH O (±)-2.49: hyperjapone A 13C NMR 125 MHz

CDCl3

69 O O

O H OH O 2.60 1H NMR 500 MHz

d6-acetone

O O

O H OH O 2.60 1H NMR 500 MHz

d6-acetone

70 O O

O H OH O 2.60 13C NMR 125 MHz

d6-acetone

O O

O H OH O 2.60 COSY 500 MHz d6-acetone

71 O O

O H OH O 2.60 HSQC 500 MHz d6-acetone

O O

O H OH O 2.60 HMBC 500 MHz d6-acetone

O O

O H OH O 2.60 1H NMR 500 MHz

CDCl3

O O

O H OH O 2.60 1H NMR 500 MHz

CDCl3

O O

O H OH O 2.60 13C NMR 125 MHz

CDCl3

74 H O O

HO H OH O (±)-2.56: hyperjaponol C 1H NMR 500 MHz

CDCl3

H O O

HO H OH O (±)-2.56: hyperjaponol C 1H NMR 500 MHz

CDCl3

75 H O O

HO H OH O (±)-2.56: hyperjaponol C 13C NMR 125 MHz

CDCl3

76 H O O

HO H OH O (±)-2.56: hyperjaponol C COSY 500 MHz CDCl3

H O O

HO H OH O (±)-2.56: hyperjaponol C HSQC 500 MHz CDCl3

H O O

HO H OH O (±)-2.56: hyperjaponol C HMBC 500 MHz CDCl3

H O O

HO H OH O (±)-2.56: hyperjaponol C ROESY 500 MHz CDCl3

78 H O O

HO H OH O (±)-2.56: hyperjaponol C 1H NMR 500 MHz

d6-acetone

H O O

HO H OH O (±)-2.56: hyperjaponol C 1H NMR 500 MHz

d6-acetone

79 H O O

HO H OH O (±)-2.56: hyperjaponol C 13C NMR 125 MHz

d6-acetone

80 O O

HO H OH O

(±)-2.54: hyperjaponol A 1H NMR 500 MHz

CDCl3

O O

HO H OH O

(±)-2.54: hyperjaponol A 1H NMR 500 MHz

CDCl3

81 O O

HO H OH O

(±)-2.54: hyperjaponol A 13C NMR 125 MHz

CDCl3

82 O O

HO H OH O

(±)-2.54: hyperjaponol A COSY 500 MHz CDCl3

O O

HO H OH O

(±)-2.54: hyperjaponol A HSQC 500 MHz CDCl3

83 O O

HO H OH O

(±)-2.54: hyperjaponol A HMBC 500 MHz CDCl3

O O

HO H OH O

(±)-2.54: hyperjaponol A ROESY 500 MHz CDCl3

84 H H O O O O

H + H H H OH O OH O 2.50: hyperjapone B 2.52: hyperjapone D

d.r. 2.5:1 1H NMR 500 MHz

d6-acetone

H H O O O O

H + H H H OH O OH O 2.50: hyperjapone B 2.52: hyperjapone D

d.r. 2.5:1 1H NMR 500 MHz

d6-acetone

85 H H O O O O

H + H H H OH O OH O 2.50: hyperjapone B 2.52: hyperjapone D

d.r. 2.5:1 13C NMR 125 MHz

d6-acetone

86 H O O

H H OH O 2.50: hyperjapone B 1H NMR 500 MHz

d6-acetone

H O O

H H OH O 2.50: hyperjapone B 1H NMR 500 MHz

d6-acetone

87 H O O

H H OH O 2.50: hyperjapone B 13C NMR 125 MHz

d6-acetone

88 H O O

H H OH O 2.50: hyperjapone B COSY 500 MHz d6-acetone

H O O

H H OH O 2.50: hyperjapone B HSQC 500 MHz d6-acetone

89 H O O

H H OH O 2.50: hyperjapone B HMBC 500 MHz d6-acetone

H O O

H H OH O 2.50: hyperjapone B NOESY 500 MHz d6-acetone

90 HO OH H

OH O 2.83 1H NMR 500 MHz

CD3OD

HO OH H

OH O 2.83 13C NMR 125 MHz

CD3OD

HO O H

OH O (+)-2.84: norisoleptospermone 1H NMR 500 MHz

d6-DMSO

HO O H

OH O (+)-2.84: norisoleptospermone 1H NMR 500 MHz

d6-DMSO

92 HO O H

OH O (+)-2.84: norisoleptospermone 13C NMR 125 MHz

d6-DMSO

93 H H O O O O H + H H H H H OH O OH O 2.51: hyperjapone C 2.53: hyperjapone E

d.r. 2.5:1 1H NMR 500 MHz

d6-acetone

H H O O O O H + H H H H H OH O OH O 2.51: hyperjapone C 2.53: hyperjapone E

d.r. 2.5:1 1H NMR 500 MHz

d6-acetone

94 H H O O O O H + H H H H H OH O OH O 2.51: hyperjapone C 2.53: hyperjapone E d.r. 2.5:1 13C NMR 125 MHz

d6-acetone

95 O O O O H + H

H H OH O OH O 2.85 2.86

d.r. 1:1 1H NMR 500 MHz

d6-acetone

O O O O H + H

H H OH O OH O 2.85 2.86

d.r. 1:1 1H NMR 500 MHz

d6-acetone

96 O O O O H + H

H H OH O OH O 2.85 2.86 d.r. 1:1 13C NMR 125 MHz

d6-acetone

97 O O O O H + H

H H OH O OH O 2.85 2.86

d.r. 1:1 1H NMR 500 MHz

CDCl3

O O O O H + H

H H OH O OH O 2.85 2.86

d.r. 1:1 1H NMR 500 MHz

CDCl3

98 O O O O H + H

H H OH O OH O 2.85 2.86

d.r. 1:1 13C NMR 125 MHz

CDCl3

99 O O O O +