关键词： Diversum var aureum   Melanin biosynthesis   Deoxygenation   Oxaziridines   Metabolites   Mechanism   Chemistry   Reductase   Acid   Absolute configuration   Reductase   oxaziridine   Efficient Protocol   Chemistry   Deoxidation   Asymmetric synthesis   metabolites   acids   silyl enol ethers  

摘要： A short and efficient protocol for the asymmetric synthesis of cis- and trans-3,4-dihydro-2,4,8-trihydroxynaphthalen-1(2H)-one (1 and 2, resp.) is described, with a phthalide annulation as the key step. Introduction of a OH substituent at position 2 was performed by Sharpless dihydroxylation of a silyl enol ether or by means of an N-sulfonyloxaziridine. The absolute configuration of each isomer was determined via Mosher-ester derivatives. By comparison with previously recorded CD spectra of our natural sample, we established that the natural trans- and cis-isomers from Ceratocystis fimbriata sp. platani were the (-)-(2S,4S)-isomer (-)-2 and the (+)-(2S,4R)-isomer (+)-1, respectively.

关键词： amino alcohols   diastereoselectivity   lactols   Michael addition   nitroalkenes  

摘要： The "naked" alkoxide 1 of (S)-6-methyl-δ-lactol acts as an excellent chiral hydroxide equivalent in highly diastereoselective oxy-Michael additions to nitroalkenes (see scheme). The excellent stereoinduction arises from what becomes a superb protecting group in the resulting 1,2-amino alcohol products. R1 = alkyl, aryl, furanyl, thiophenyl; R2,R 3 = -(CH2)3CHCH3O-.

关键词： Catalysis   Diastereoisomers   Asymmetric synthesis   Hong Kong Polytechnic University -- Dissertations  

摘要： Asymmetric catalysis is an important subject in science and *** thesis focused on the development of novel C2-symmetric diphosphine ligands possessing additional chiral centers on the backbones and their applications in asymmetric hydrogenation reactions；Diastereomeric biaryl diphosphine ligands (S)- or (R)-[5,5',6,6'-bis(2R,4R-pentadioxy)]-(2,2')-bis(diphenylphosphino)-(1,l')-biphenyl with added chiral centers on the backbone were synthesized. Substrate-directed asymmetric synthesis occurred in the Ullmann coupling step for the preparation of the diastereomeric diphosphine oxides. The diastereomeric diphosphine oxides were easily by column chromatography with silica gel. Ruthenium catalysts containing these ligands were more effective than the BINAP catalytic systems in the hydrogenation of 2-(6'-methoxy-2'-naphthyl)propenoic acid (up to 97% ee) and B-ketoesters (up to > 99% ee). The additional chiral centers exhibited a significant influence on the enantioselectivity and activity of the catalysts；C2-symmetric biphenyl phosphine ligand (S)-[6,6'-(2R,4R-pentadioxy)]-(2,2')-bis (diphenylphosphino)-(1,l')-biphenyl possessing a chiral bridge to link the biphenyl groups was prepared. Complete atropdiastereoselectivity was realized for the first time in the preparation of biaryl diphosphine oxide via asymmetric intramolecular Ullmann coupling with central-to-axial chirality transfer. The effect of precise chiral recognition was also clearly revealed in a related asymmetric ring closure reaction. Ligands (S)-[6,6'-(2R,5R-hexadioxy)]-(2,2')-bis(diphenylphosphino)-(1,1')-biphenyl and (R)-[6,6'-(2S,3S-butadioxy)]-(2,2')-bis(diphenylphosphino)-(l,l')-biphenyl were prepared via the ring closure route, too. The stereorecognition abilities of the corresponding Ru complexes for the three ligands compared favorably with Ru(BINAP) or Ru(MeO-BIPHEP) complex in the same model reactions. The introduction of additional chiral centers offered opportunities for structurally f

关键词： sulfoxide   sulfinyl group   asymmetric synthesis   chiral auxiliary   chiral ligand  

摘要： Chiral sulfinyl groups have been widely used in organic synthesis as a stereo- and enantiodirecting functionality and the high efficiency of the selectivity has received much attention in recent years. In this review we wish to cover the work published in the literature since 1996. The participation of a chiral sulfinyl function in a wide range of reactions as well as the application of these methodologies to the synthesis of natural products are reported.

关键词： 氨基酸   催化剂   不对称合成   聚合物  

摘要： 20世纪80年代发现聚氨基酸(由10~30个相同的氨基酸聚合而成)可以用作有机不对称合成反应的催化剂,由于其潜在的理论研究价值和在工业合成中的应用前景,科研工作者正努力揭示其催化机理以及试图大规模应用于工业合成.本文结合本实验室的研究工作,讨论聚氨基酸在不对称合成反应中的应用.

关键词： 不对称合成   α-取代-γ-丁内酯   非酶动力学拆分   酮咯酸  

摘要： 近30年来,不对称合成成为有机化学学科最活跃的领域之一.随着手性技术的进步,推动了手性药物、材料科学等的发展.开展对单一光学异构体药物的研究,对减少药物剂量、降低毒副作用很有意义,是有机化学、药物化学研究中极具挑战性的课题,具有重要的学术价值和应用前景.该论文的一部分工作采用辅基控制法,利用脯氨醇型辅基,合成了手性的α-取代-γ-丁内酯,其是天然存在的生物活性分子和天然药物中的重要结构砌块.其中从L-脯氨酸出发,合成了三种类型共9个(S)-(-)-二烃基(1-烷酰基吡咯烷-2-基)甲醇衍生物,经LDA处理和烷基化反应,通过金属离子参与配位的烯醇锂过渡态,生成不对称选择性烷基化产物,经水解得到三种类型手性α-取代-γ-丁内酯,其﹪e.e.最高可达89﹪.论文的另一部分工作是以手性胺为试剂,首次对外消旋非甾体消炎镇痛药酮咯酸进行了非酶动力学拆分.用合成的外消旋酮咯酸与DEPBT缩合得到的活泼酯中间体(10)作为动力学拆分的底物,用(S)-(-)-α-苯乙胺或(R)-(+)-α-苯乙胺进行动力学拆分,在优化的反应条件下,分别得到了(S)-(-)-酮咯酸和(R)-(+)-酮咯酸,其中得到的具有高生物活性的(S)-(-)-α-酮咯酸的﹪e.e.最高达到39﹪,而(R)-(+)-酮咯酸的﹪e.e.最高达到32﹪.用X-ray四圆衍射仪分别测定了(S)-(-)-α-苯乙胺和(S)-脯氨酸苄酯与酮咯酸形成的一种酰胺,结合TLC和<'1>HNMR监测反应的结果,确定了动力学拆分中的快反应和慢反应.该论文还对酮咯酸的直接不对称合成进行了探索.经过砌块模型试验,合成了关键的中间体化合物,但是采用金属配合物的催化反应没有得到预期结果.论丈采用<'1>HNMR、<'13>CNMR、MS、旋光值、HRMS或元素分析,对所合成的化合物的结构进行了鉴定.

关键词： Direct optical resolution   Diels-alder reaction   Ring-opening reactions   Transfer hydrogenation   Antitumor-activity   Ligands   Acid   Complexes   Catalysis   2   2'-dihydroxy-1   1'-binaphthyl  

摘要： The simple and highly enantioselective methanolysis of norbornene dicarboxylic acid anhydride mediated by quinidine leads to the corresponding cis-monomethyl ester with 98% ee. By means of selective ester epimerization, followed by Curtius degradation of the intermediate trans-diacyl azide, two optically active norbornane-type diamines are obtained as their hydrochloric salts. Liberating the amine with an excess of triethylamine in situ and subsequent derivatization affords potential C-1-symmetric ligands for asymmetric catalysis in excellent yields.

摘要： The total synthesis of pectenotoxin-4 has been achieved in 37 linear steps from commercially available material and 0.3% overall yield. The chiral building blocks for the synthesis were derived from catalytic enantioselective reactions, chiral auxiliary based chemistry, D-mannitol, and lactic acid. Felkin-controlled addition to aldehydes, chelate-controlled reduction of ketones, directed epoxidation of olefins, and iodoetherification reactions were used to internally relay stereochemistry and access the highly oxygenated structure of the pectenotoxins. Key bond constructions include a metalloenamine-epoxide alkylation, late stage olefination, and macrocyclization. The use of the N-phenylamide as a carboxyl surrogate, and the utility of the previously unused tert-butoxydiphenylsilyl ether protective group in a multistep synthesis is also described. Synthetic pectenotoxin-4 was isomerized to pectenotoxin-8 upon exposure to mild acid.* *Please refer to dissertation for diagrams.

关键词： allylation   amino acids   enantioselectivity   iridium   P ligands  

摘要： Simply switching the base employed in the first enantioselective allylic substitutions of diphenylimino glycinate 1 with 2, which are catalyzed by an Ir complex of chiral phosphite 5, allows the two branched diastereomers 3 and 4 to be selectively synthesized with little or no formation of linear substitution products.

关键词： amino acids   asymmetric catalysis   chirality   diastereoselectivity   enantioselectivity  

摘要： The stereoselective synthesis of amino acids is of great importance for the construction of optically active natural products and pharmaceuticals. Apart from enzymes, a broad repertoire of chiral reagents, auxiliaries, and catalysts can be used for the formation of amino acids. Asymmetric reactions using catalytic amounts of chiral molecules provide efficient methods for the generation of optically active proteinogenic and nonproteinogenic amino acids. This minireview collects recent work on catalytic asymmetric synthesis of α- and β-amino acids.