关键词： anatoxin   enantioselective deprotonation   natural products   total synthesis  

摘要： In only seven steps a formal synthesis of enantiomerically enriched (+)-anatoxin-a has been achieved. This was accomplished by utilizing a highly enantioselective desymmetrization of the eight-membered ring ketone 1 to form 2, and a novel cascade reaction to construct the 9-azabicyclo[4.2.1]nonane skeleton.

关键词： CYCLIC SULFATES  

摘要： The fully substituted cyclopentene ring with three stereogenic centers has been efficiently constructed for the first time using chiral bicyclic lactams, the insertion of the quaternary center being the key step;ring opening of chiral sulfates to the correct 1,2-dihydroxy substituents also played a major role in reaching 1 in suitable form (18) for further study.

关键词： INTRAMOLECULAR BIS-SILYLATION   SAKURAI ISMS REACTION   TETRAHYDROPYRANS   ALCOHOLS   KETONES   ACETALS  

摘要： According to the protocol for the acetalization-intramolecular allylsilane cyclization, a new enantioenriched allylsilane, (R)-(E)-7-(dimethylphenylsilyl)undec-5-en-1-ol, in the presence of a variety of aldehydes provided enantioenriched trans-2,3-disubstituted oxepanes stereoselectively.

关键词： Asymmetric synthesis   Metal complexes   Chirality   Catalysis   Hong Kong Polytechnic University -- Dissertations  

摘要： Chiral phosphine ligands have played a dominant role in the development of novel transition-metal-catalyzed enantioselective synthesis. Among these evolved ligands, the type of ligands containing skewed backbone and with C₂ symmetry has been found to be highly effective and versatile in inducing the metal-catalyzed asymmetric transformations. In addition, the ligands having rigid conformational structures seem generally to be better than those which are conformationally mobile in asymmetric catalytic reactions. The results also unveil that a sterically asymmetric environment created by the chiral ligands should be the main factor responsible for the high enantioselectivity. From this point of view, the derivatives of the intrinsically skewed spirocyclic diol have attracted our attention because of the potentially useful rigid chiral backbone. Therefore, the preparation of optically pure spirodiols and subsequently various transformations of the ***-spiro[4,4]nonane-l.6-diol to chiral auxiliaries such as organophosphines and amines have been studied. The further development of the novel chiral ligands applying spiro-derivatives as the backbone and practical utility of the spiro-containing catalysts in some asymmetric catalytic reactions are the focal point of the research. The desired optically active cis,cis-l,6-diamino-spiro[4,4]nonane has been prepared successfully and transformed to corresponding cis,cis-l,6-Bis(diphenylphosphino-amino)spiro[4,4]nonane. This novel chiral aminophosphine was proven to give a highly efficient Rh(I) catalyst for the asymmetric hydrogenation of dehydro α-amino acid esters and showed excellent enantioselectivities ranged from 94 to over 99% ee. The hydrogenation of methyl enol acetate and ethyl enol acetate catalyzed by the same Rh(I) catalyst gave the enantioselectivities of 96.2 and 96.7% respectively. Furthermore, the hydrogenation of dimethyl itaconate catalyzed by the spirodiaminophosphine-Rh(I) complex resulted the hydrogenat

摘要： The pheromone, (+)-cis-2-isoprenyl-1-methylcyclobutene-ethanol 1, commonly known as (+)- grandisol was synthesized in a 95+2Vo e. e. via an allylic alcohol, [(lS,5R)-5- methylbicyclo[3.2.0]hept-2-en-2-yll methanol 38, as the key intermediate.. OPtical activity was induced in the primary alcohol by a kinetic resolution reaction which the Sharpless asymmetric epoxidation reaction. Two routes from (1SR,5sR)-5-methylbicyclo[3.2.0]heptan-2-one 12 to this key intermediate compound were explored. One was unsuccessful, the other allowed the synthesis of the allylic alcohol in four steps from commercially available sources. Functional group interconversion of the allylic alcohol gives exclusively fhe endocyclic alkene, (1S,5R)-2,5-dimethylbicyclo[3.2.0]hept-2-ene 10. Conversion of the endocyclic alkene to (+)- grandisol, by a combination of procedures previously established in the literature by two groups, was accomplished in four steps. The requirements necessary for a highly selective kinetic resolution using the Sharpless asymmetric dihydroxylation reaction were investigated. Three different bicyclic alkenes were studied, (1S,5R)-2,5-dimethylbicyclo[3.2.0]hept-2-ene 10, (1SR,5SR)-5-methyl-2-methylene bicyclo[3.2.0]heptane 9, and (1RS,5SR)-5-methyl-2-phenylbicyclo[3.2.0]heptan-2-ene L25. The Sharpless dihydroxylation reaction was diastereoselective in all cases, however high enantioselectivity was only achieved with the last alkene. This is consistent with substrate control in the asymmetric dihydroxylation reaction. The pheromone, (1S)-1-methyl-2-cyclohexenol (MCL) 2 was synthesized in a 94+37o e. e. in three steps from 1-methylcyclohexene via a 'merged substitution-elimination reaction' involving phenylselenide anion. The stereochemistry was achieved by the Sharpless asymmetric dihydroxylation reaction.

摘要： This thesis presents the results of studies aimed at the development of general strategies for the synthesis of azasugars, which act as glycosidase inhibitors. In the first Chapter a review is made of the role of carbohydrates and glycosidases in biological systems. The strategies developed for the synthesis of azasugars are discussed, as well as the aims of this project and the literature relevant to the synthetic aspects of this project. The successful synthesis of γ-amino-α,β-unsaturated ketones from allylic sulfoximines utilising a palladium(O) catalysed rearrangement is presented in Chapter 2. The regioselectivities and diastereoselectivities of these transformations are also discussed. In Chapter 3, the palladium(O) catalysed amination of allylic sulfoximines utilising external nucleophiles is described. The regioselectivities of these reactions with various allylic sulfoximines is reported, as are the results of competition reactions between the external nucleophile and the sulfinamide anion. The results of attempts to induce asymmetry into the reaction via the use of enantiomerically pure sulfoximines, chiral ligands and chiral external nucleophiles are also discussed. The attempted synthesis of azasugars from allylic sulfoximines is presented in Chapter 4. Results from investigations into the use of both the intramolecular rearrangement examined in Chapter 2 and the allylic amination reaction described in Chapter 3 towards the synthesis of azasugars are detailed. In Chapter 5, the attempted synthesis of azasugars from a carbohydrate source is reported. The key steps in the synthetic path are elongation via Grignard addition, palladium(O) catalysed allylic amination, oxidation of a double bond and cyclisation. A brief summary of the work carried out in this thesis is provided in Chapter 6, as well as current and future work in this area.

关键词： asymmetric synthesis   chelates   chiral auxiliaries   ferrocenyl ligands   hydrazones  

摘要： A stereogenic center at the position β to the metallocene backbone is present in ferrocenyl ligands 2, which are interesting for asymmetric catalysis. These planar-chiral compounds are accessible for the first time by a highly diastereoselective and enantioselective synthesis (de=93-97 %; ee≥96 %) from the ferrocenyl ketones 1. A variety of donor groups (E1=Ph2PBH3, SMe, SiPr; E^2=SMe, STol, SePh, Ph2PBH3, iPr2PBH3) can be introduced as electrophiles. Tol=tolyl=CH3C6H4.

关键词： nakijiquinones   protein kinase inhibitors   signal transduction   terpenoids   total synthesis  

摘要： A Wieland-Miescher type ketone and a tetramethoxyaryl derivative are the key building blocks for the enantioselective total synthesis of nakijiquinone C (1). The nakijiquinones are the only natural products known that selectively inhibit the Her-2/Neu tyrosine kinase, a protooncogene product that is vastly overexpressed in about 30 % of primary breast, ovary, and gastric carcinomas.

关键词： Reaction products   Precursors   Stereoselectivity   Molecular structure   Alkyls  

关键词： 嘌呤   嘧啶   不对称合成   晶体结构   手性化合物  

摘要： 把具有生理活性的嘌呤、嘧啶类有机碱基引入不对称合成 ,利用嘌呤、嘧啶类化合物作为Michael加成给体与天然手性助剂 ( - ) 薄荷醇所制得的手性源 5 (R) [( 1R ,2S ,5R) 氧基 ] 2 ( 5H) 呋喃酮 ( 3a)进行不对称Michael加成反应 ,合成了新的光学纯嘌呤、嘧啶类手性化合物 ( 5a～ 5e) .详细地研究了合成方法并测定了它们的[α],IR ,UV ,1HNMR ,13 CNMR ,MS ,元素分析等结构分析数据 .经X 四圆衍射确定了腺嘌呤手性化合物 5a的立体化学结构 .为合成嘌呤、嘧啶类手性化合物提供了有效的途径 。