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

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： β-环糊精   β-环糊精聚合物   不对称合成   超分子催化剂   包络化合物  

摘要： 该论文主要研究了环糊精和环糊精聚合物有机合成中的应用.文中首先对环糊精在有机合成中的应用及环糊精聚合物的合成、应用和高分子效应等方面作了介绍,据此提出了课题设想.论文工作主要分为两部分:第一部分为环糊精诱导的苯乙酮不对称还原反应的研究;第二部分为环糊精聚合物作为超分子催化剂的研究.

关键词： asymmetric synthesis   cycloadditions   cyclobutanones   metalations   silicon  

摘要： An asymmetric allylmetalation followed by a silicon-stereodirected cycloaddition gives enantiomerically pure bicyclic compounds. The synthesis of enantiopure 1 (see scheme) in a yield of 65-74 %, 93 % ee, and >98 % de provides an illustration of the efficacy of the method. The preferential formation of 1 rather than its diastereoisomer (32:1), during the cycloaddition step, matches the result predicted by RHF and density functional theory studies.

关键词： alkenes   asymmetric synthesis   biaryls   chirality   helical structures  

摘要： Optically active overcrowded alkenes were synthesized by employing bis-β-naphthol as a chiral template during an intramolecular coupling reaction. The major isomer 2 has a unique helical structure with twisted and folded structural moieties. Removal of the chiral template afforded overcrowded thioxanthylidene 3 with 96 % ee, which indicates that no racemization or isomerization of the enantiomers took place.

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： Allylic alkylation   Asymmetric catalysis   Palladium catalysis   Vitamin E analog  

摘要： An asymmetric synthesis of the vitamin E core derives from the employment of the palladium catalyzed asymmetric allylic alkylation (AAA) reaction. The requisite substrate, available in 7 steps from trimethylhydroquinone, involves asymmetric creation of a quaternary center. In contrast to literature reports using a wide variety of asymmetric ligands which gave a maximum ee of 54%, the ligand derived from trans-1,2- diaminocyclohexane and 2-diphenylphosphinobenzoic acid gave an 84-87% ee in 89-96% yield. Asymmetric induction derives from chiral recognition of the enantiotopic faces of the substrate during the ionization event.

关键词： asymmetric amplification   asymmetric synthesis   autocatalysis   chirality   circularly polarized light  

摘要： Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems. The photoresolution of the enantiomers of helical-shaped, sterically overcrowded alkene 1 with circularly polarized light and the transduction of the stereochemical information by triggering the helical arrangement of a large collection of achiral molecules in a twisted nematic liquid crystalline phase (2) are examples of control and amplification of chirality.

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.