published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Dong, Jiaqiang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 169-186). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

*Please refer to dissertation for diagrams. / Chapter 2 is concerned with the aim of our research work, retrosynthetic analysis and strategy. Herein, we report the synthesis of the pivotal precursor aldehyde (112) by a Grob fragmentation procedure. In addition, model studies of the key biomimetic aldol cyclization are also discussed. We completed the total synthesis of the two novel diterpenes (+/-)-( 1) and (+/-)-(2) via intramolecular Michael reaction and alpha-ethylidenation starting from (+/-)-Wieland-Miescher ketone. / In Chapter 1, an overview of the isolation, structure elucidation and bioactivities of pallavicinin (1) and neopallavicinin ( 2) are presented. In addition, various synthetic approaches toward the analogous skeletons of the two novel diterpenes are reviewed. / In Chapter 3, a brief conclusion is provided.* / Two novel diterpenes, named pallavicinin (1)and neopallavicinin (2)were first isolated from liverwort Pallavicinia subciliata by Wu16 and their coworkers in 1994. These compounds show potential bioactivities, such as antipyretic properties, muscle regeneration and detoxification.17,18 The diverse structural features of these novel diterpenes in conjunction with their potential bioactivities have stimulated our considerable interest in the quest for their total synthesis. / Peng Xiahshui. / "April 2006." / Adviser: Henry N. C. Wong. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6412. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

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published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The enantioselective approach to bonandiol, also known as magydardiendiol, has utilized two novel synthetic methodologies. The first is the diastereoselective cyclopropanation of a homochiral eneketal prepared from (2R,3R)- or (2S,3S)-2,3-butanediol and possessing C₂ symmetry. Simmons-Smith cyclopropanation gave good diastereoselectivity (69-75%) in addition to excellent amounts of monocyclopropanated material obtained (90-96%). The second method utilized is the nickel acetylacetonate catalyzed coupling of dimethylzinc to a sterically hindered cyclic β-keto enolphosphate in 76-92% yield. This approach to the A ring of hyperforin starting from commercially available citral allows for the introduction of all but one isoprenyl appendage.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

by Ching-hung Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 75-78). / Chapter i --- Biography / Chapter ii --- Abstract / Chapter iii --- Acknowledgments / Chapter iv --- Abberivations / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Review on the published syntheses of Zoapatanol --- p.1 / Chapter 1.2 --- Review on the construction of the oxepane ring --- p.7 / Chapter 1.3 --- "Review on the intramolecular nitrone and nitrile oxide 1,3-dipolar cycloaddition" --- p.15 / Chapter 1.3.a. --- Nitrone-olefin cycloaddition --- p.16 / Chapter 1.3.b. --- Nitrile-oxide-olefin cycloaddition --- p.17 / Chapter 1.4 --- Isoxazoline Transformation --- p.18 / Chapter Chapter 2 --- Results and Discussion / Chapter 2.1 --- General Aspect --- p.19 / Chapter 2.2 --- "Entries to 6 and 7-membered O-heterocycles via 1,3-dipolar nitrone cycloaddition" --- p.21 / Chapter 2.3 --- "Entries to 6 and 7-membered O-heterocycles via l,，3-diploar nitrile oxide cycloaddition" --- p.33 / Chapter 2.4 --- Conclusion --- p.47 / Chapter Chapter 3 --- Experimental / General --- p.49 / Experimental --- p.51 / References --- p.75

The preparation of bicyclic systems containing an allylic, angular hydroxyl group (general structure 20 and compound 87b) is described. These materials have been prepared via a new annulation sequence involving (a) the alkylation of cyclic ketones with the bifunctional conjunctive reagents 129, 21 and 60, (b) the conversion of the alkylation products into keto vinyl iodides, and (c) cyclization of the keto vinyl iodides via low temperature metal halogen exchange with n-butyllithium. The cyclization process described in (c) has been employed in the first total synthesis of the diterpenoid (±)-ambliol B (94). Thus, 3,4-dimethyl-2-cyclohexen-l-one (96) was converted, in three steps, into the unstable enone 125. Reaction of this compound with the novel vinylgermane cuprate 110, followed by reaction of the resultant product with iodine, gave the cyclization precursor 106. Cyclization of 106 gave a single, trans-fused product (128) in high yield. The exocyclic methylene function of 128 was cyclopropanated and the vinyl substituent of the resultant cyclopropane was hydroborated to give the cyclopropane diol 149. Hydrogenolysis of the cyclopropane ring of compound 149 provided the required gem-dimethyl moiety. The resultant product was converted into (±)-ambliol B (94) via a four step sequence of reactions involving (a) oxidation of the primary alcohol function, (b) addition of 3-furyllithium to the so-formed unstable aldehyde, (c) acetylation of the secondary alcohol prepared in (b), and (d) reductive removal of the acetoxy function. A new annulation sequence which utilizes the vinylgermane cuprate 110 as a synthetic equivalent of the 1-butene a²,d⁴-synthon 153 is described. Thus, cyclic enones of the general structure 154 were treated with 110 to provide the keto vinylgermane intermediates 155. The latter materials were transformed into the corresponding keto vinyl iodides 156. Treatment of 156 with a palladium(0) catalyst and a base resulted in cyclization to provide the annulation products 157 or, when R₁ = H, the α,β-unsaturated ketones 185. [ Formulas omitted ] / Science, Faculty of / Chemistry, Department of / Graduate