Au, Ching Chi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 83-89). / Abstracts in English and Chinese. / Table of contents --- p.i / Acknowledgements --- p.iii / Abbreviations --- p.iv / Abstract --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Importance of Transition Metal Amido Complexes --- p.1 / Chapter 1.1.1 --- Transition Metal Amido Complexes as Catalysts --- p.1 / Chapter 1.1.2 --- Transition Metal Amido Complexes as Reaction Intermediates --- p.2 / Chapter 1.2 --- Bonding Nature of Late Transition Metal Amido Complexes --- p.4 / Chapter 1.2.1 --- Theory of π Conflict --- p.5 / Chapter 1.2.2 --- E-C Approach --- p.7 / Chapter 1.3 --- Synthesis of Transition Metal Amido Complexes --- p.8 / Chapter 1.3.1 --- Transmetallation --- p.9 / Chapter 1.3.2 --- Deprotonation of Coordinated Amine --- p.10 / Chapter 1.3.3 --- Hydride Addition across Organic Azide --- p.11 / Chapter 1.4 --- Reactivity of Transition Metal Amido Complexes --- p.12 / Chapter 1.4.1 --- β-Elimination --- p.12 / Chapter 1.4.2 --- Insertion --- p.13 / Chapter 1.4.3 --- Reductive Elimination --- p.16 / Chapter 1.4.4 --- Bond Activation --- p.17 / Chapter 1.5 --- Structural Features of Rhodium Porphyrin Complexes --- p.18 / Chapter 1.6 --- Examples of Metalloporphyrin Complexes Containing Nitrogen Ligands --- p.19 / Chapter 1.7 --- Bond Activation by Rhodium Porphyrins --- p.21 / Chapter 1.8 --- Objectives of the Work --- p.23 / Chapter Chapter 2 --- Synthesis and Reactivity Studies of Rhodium Porphyrin Amido Complexes --- p.24 / Chapter 2.1 --- Synthesis of Porphyrin and Rhodium Porphyrin Chloride --- p.24 / Chapter 2.2 --- Synthesis of Rhodium Porphyrin Amido Complexes from Rhodium Porphyrin Chloride --- p.24 / Chapter 2.2.1 --- By Transmetallation with Lithium Amide --- p.25 / Chapter 2.2.2 --- By Base-promoted Ligand Substitution Using Rh(ttp)Cl --- p.27 / Chapter 2.2.2.1 --- Optimization of Reaction Conditions --- p.27 / Chapter 2.2.2.2 --- Substrate Scope --- p.31 / Chapter 2.3 --- X-ray Structure of Rh(ttp)NHS02Ph --- p.33 / Chapter 2.4 --- Bond Activation Chemistry of Rh(ttp)NHS02Ph --- p.36 / Chapter 2.5 --- Conclusion --- p.37 / Chapter Chapter 3 --- Reactivity Studies of Rh(ttp)NHS02Ph --- p.39 / Chapter 3.1 --- Thermal Reaction of Rh(ttp)NHS02Ph in Benzene-d6 --- p.39 / Chapter 3.2 --- Mechanistic Studies of the Conversion from Rh(ttp)NHS02Ph to [Rh(ttp)]2 --- p.41 / Chapter 3.2.1 --- Mechansim A (Hydrolysis of Rh(ttp)NHS02Ph) --- p.42 / Chapter 3.2.2 --- Mechanism B (Rh-N Bond Homolysis - (PhS02NH)2 Hydrolysis) --- p.44 / Chapter 3.2.3 --- Mechanism C (Rh-N Bond Homolysis - (PhS02NH)2 Nitrogen-Hydrogen Bond Activation) --- p.45 / Chapter 3.3 --- Discussions --- p.52 / Chapter 3.3.1 --- Estimation of Rhodium-Nitrogen Bond Dissociation Energy --- p.52 / Chapter 3.3.2 --- Effect of Excess PhS02NH2 in the Synthesis of Rh(ttp)NHS02Ph --- p.58 / Chapter 3.4 --- Conclusion --- p.58 / Chapter Chapter 4 --- Experimental Section --- p.60 / References --- p.83 / Appendix I X ray data --- p.90 / Appendix I List of Spectra --- p.96

The primary aim of this project was to synthesize new heterocyclic dimers of isoflavones and flavones, and investigate various methodologies for their synthesis. The secondary aim of the project was to synthesize some flavonoid natural products. Dimeric systems were synthesized using various methodologies including acid catalyzed arylation of isoflavanols and flavanols, acid catalyzed dimerization of flavenes, oxidative dimerization, Sonogashira coupling, Ullmann coupling and Suzuki-Miyaura coupling reactions. The acid catalyzed arylation of isoflavanols was found to proceed in a very stereoselective fashion to give trans-4-arylisoflavans in good yield in a single step. However, related flavanols under similar conditions gave mixtures of cis and trans isomers of 4-arylflavans. Interestingly, it was found that appropriately substituted flavenes, upon treatment with acid undergo stereoselective rearrangement and dimerization to give benzopyranobenzopyrans in high yields. A rationale for the rearrangement is proposed and this dimerization was used for the stereoselective synthesis of the natural product dependensin. As part of the project, some polycyclic natural products such as octandrenolone, flemiculosin, 3-deoxy-MS-II and laxichalcone were also synthesized. Oxidative dimerization of activated isoflavones was found to be very regioselective, and novel isoflavone dimeric systems were synthesized. Related flavones however, failed to undergo dimerization under similar conditions. A probable explanation for high regioselectivity in the case of isoflavones and unreactivity of flavones has been presented. Phenol oxidative coupling was used for the one-step synthesis of another natural product kudzuisoflavone-A from daidzein. Sonogashira coupling was utilized for the synthesis of dimeric systems linked via an acetylic linker. A variety of soflavone isoflavone, flavone-flavone and isoflavone-flavone dimers were synthesized in "one-pot" by this methodology and in excellent yields. Although Ullmann coupling was found not to be suitable for the synthesis of isoflavone or flavone dimers, one-pot Suzuki-Miyaura methodology gave flavone dimers and various other heterocyclic dimers in good yields.

PART I. A deuterium exchange analysis of 2,5-dihydroxyacetanilide (5) in the absence and presence of DHAE II was performed to test the nucleophilicity of the substrate in the absence and presence of catalyst. In addition, inhibition studies using 1,4-dihydroxybenzene were performed to determine the role that the N-acetyl side chain group plays in the formation of a stable substrate-enzyme complex. 1,4-Dihydroxybenzene was found to be a weak inhibitor, indicating that the N-acetyl functionality may play a crucial role in forming stable enzyme-substrate interactions. The synthesis of dihydroquinoline 7 was pursued to investigate the enzyme substrate interactions between DHAE and a substrate where the N-acetyl side chain has been fixed to a particular orientation. Efforts towards formation of the C6-C7 bond as a key step in the synthesis of dihydroquinoline 7 using palladium couplings, organocuprates, Lewis acid catalysts, and aza-Claisen reactions were pursued. To complement the results obtained, the electron distribution in amide 21 was calculated using Semi Empirical methods. The results revealed that the electron density in the aromatic ring is centered around C4, suggesting that this is the most nucleophilic carbon in the ring. PART II. Slagenins A (1), B (2), and C (3) were synthesized by β-functionalization of olefin 14. The desired tetrahydrofuroimidazolidin-2-one system was achieved by intramolecular oxidative addition of alcohol 4 to the imidazolone ring. When this reaction was carried out in the presence of methanol slagenins B (2) and C (3) were obtained in good yield. Heating 2 and 3 in aqueous acid gave slagenin A (1) as the sole product. (Z)-debromoaxinohydantoin (17) was synthesized by intramolecular cyclization of α-methoxy imidazolone 11b under acidic conditions followed by a double oxidation reaction to furnish the hydantoin-lactam functionality. These conditions were originally developed for a practical synthesis of the related alkaloid (Z)-debromohymenialdisine (20). A series of acid and base catalyzed reactions of imidazoles bearing an α-β unsaturated system or a β-halogen functionality showed that cyclizations via an S[subscript N]2 path favor formation of an oxazoline ring system. Preliminary studies using pyrrolocarboxamideacetals suggest that β-ketone 73 would be an appropriate substrate for the formation of the pyrrolopyrazine system in the agelastatins. / Graduation date: 2002

Graduation date: 2003

Graduation date: 2003

Studies toward synthesis of subunits of sanglifehrin A, an immunosuppressant featuring a highly substituted [5,5]-spirolactam moiety as well as a 22-membered macrocycle are described. The macrolactone contains a peptidic backbone characterized by an unusual [beta]-substituted (S)-piperazic acid and (S)-m-hydroxyphenylalanine units. These studies resulted in the synthesis of advanced intermediate 358 which contains all of the carbon atoms of the C1-C25 macrolactone of sanglifehrin A, and 251 which bears the C31-C41 carbon skeleton of the [5,5]-spirolactam moiety of sanglifehrin A. A Masamune anti-aldol reaction of aldehyde 294 and ester 285 furnished alcohol 295 in a second generation approach to carboxylic acid 242, while a third generation route toward 242 improved the yield and required fewer synthetic steps. An asymmetric, catalytic phase-transfer method was used to introduce an [alpha]-amino function into 331 in the synthesis of (S)-m-hydroxyphenylalanine derivative 244. Assembly of 244, piperazic acid 113 and L-valine derivative 336 into tripeptide 241 using a racemization-free peptide coupling method is described. The synthesis of C31-C37 aldehyde 253 exploited double asymmetric crotylation to set in place the correct configuration of alternating hydroxyl and methyl groups at C33, 34, 35 and 36. / Graduation date: 2013

Graduation date: 1996

Graduation date: 1997

The thesis entitled "SYNTHETIC INVESTIGATIONS ON TERPENOIDS" consists of two chapters. Chapter I deals with the total synthesis of the sesquiterpenes, 2-pupukeanone 1 Norpatchoulenol 2 and patchouli alcohol 3 and is divided into four sections.

Two syntheses of non-cross-linked polystyrene-supported TADDOL-based phosphoric acid organocatalyst have been developed. The optimal polymer-supported catalyst 2.29d exhibited comparable catalytic activity to its small molecule counterpart in asymmetric Mannich-type reactions, and the syntheses of several chiral β-amino esters were demonstrated using 2.29d as catalyst. However, when this TADDOL-based phosphoric acid was immobilized on a polystyrene cross-linked with 1,4-bis(4-vinylphenoxy)butane, ie. JandaJelTM, the catalytic activity diminished in the first recycling and reuse of the catalyst. Building on the success of the immobilization of chiral phosphoric acid, a more robust phase-tagged BINOL-based phosphoric acid organocatalyst was developed. By taking advantage of a tetraarylphosphonium salt as a solubility-controlling group, a widely-used BINOL-based phosphoric acid, TRIP (3.1), was introduced onto a tetraphenylphosphonium salt to produce a phosphonium salt-tagged phosphoric acid catalyst 3.3e. After systematic optimizations of reaction conditions, it was found that the catalyst 3.3e with PF6 as counteranion exhibited the best performance in terms of enantioselectivity. Catalyst 3.3e was proved to be highly effective in asymmetric Friedel-Crafts reaction of indoles because it was shown to be recyclable and reusable after six cycles without loss of catalytic activity. Based on our previous studies on the reduction of unsaturated thioesters catalyzed by (BDP)CuH, further investigation of ligand effects revealed that in addition to BDP, dppf was also an effective ligand for the simple reduction of 5.8. In the stoichiometric reduction of unsaturated thioester 5.8, dppe and dppf were both efficient ligands for copper hydride that could convert 5.8 to aldehyde 5.18 in the presence of TMSCl, without the formation of the undesired enol ester 5.17, which was a major product when stoichiometric amounts of Stryker’s reagent was employed. When 5.30 bearing both a saturated and unsaturated thioester was reduced under these conditions, only the enethioate functional group underwent reaction to yield the mono-reduced product 5.31 while the saturated thioester functional group remained inert. The desymmetrizing reductive aldol reactions of symmetrical keto-enethioates 6.19, 6.22, 6.24 and 6.26 catalyzed by in situ generated chiral copper hydride were investigated. After a screening of the reaction conditions, TaniaPhos L8 was found to be the most effective chiral ligand to achieve high ee and yields. Under the optimum reaction condition (5 mol% Cu(OAc)-H2O and L8 with 2.0 eq. PhSiH3), a range of keto-enethioates smoothly underwent desymmetrizing reductive aldol cyclizations, offering bicyclic or polycyclic β-hydroxythioesters (6.28a-6.32a, 6.37a-6.47a) in 35- 84% yield and 30-97% ee with high diastereoselectivity. The addition of 5 mol% of bipyridine as additive resulted in an accelerated reaction rate in all of the reductions of keto-enethioates. The crystal structure of the L8-copper bromide complex allowed the rationalization of the major enantiomer (eg. 6.48a), in which all of the substituents are cis, to be a result of a reductively generated (Z)-thioester enolate reacting through a Zimmerman-Traxler transition state. This stereochemical outcome is in contrast to the reduction of the analogous oxoesters, which yield trans β-hydroxyesters, (eg. 6.54b), as the major products. Several proposals to explain the divergent stereochemistry, including the predominance of a Zimmerman-Traxler transition state of (E)-enolates or subsequent retroaldol rearrangements, were discussed. The retroaldol rearrangement has been observed in the conversion of 6.48a to 6.57c, in which there was retention of the configuration at C5 and a perfect conservation of enantiomeric purity. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy