关键词： 不对称合成反应   旋光特性守恒   立体化学反应   反应物   生成物  

摘要： 在某些经验规则的基础上 ,从旋光特性守恒的角度归纳分析了立体化学反应中反应物和生成物旋光特性的特点 ,并结合该特点的举例讨论了其应用 。

关键词： R-(-)-扁桃酸   不对称还原   立体选择性   手性合成   酵母细胞   催化合成  

摘要： 研究了酵母细胞(Saccharomyces cerevisiae)生物不对称还原苯乙酮酸合成R-(-)-扁桃酸的过程中,环境因子对底物的转化效率和产物对映体过量值的影响. 结果表明,高浓度的底物苯乙酮酸对酵母细胞的催化还原活性具有较显著的抑制效应. pH 6.5、温度32oC、严格厌氧为较适宜条件,底物苯乙酮酸的转化率和产物扁桃酸的得率分别可达97.0%和96.1%,R-(-)-扁桃酸的对映体过量值(ee)为95.1%.

关键词： L-[3-C-13]alanine   [C-13]methyl iodide   chiral glycine equivalent   oxazinone  

摘要： L-[3-C-13]Alanine was synthesized from [C-13]methyl iodide by using Dellaria's oxazinone, prepared from phenyl[2-C-13]bromoacetate and (S)-2-phenylglycinol, as a chiral glycine equivalent. Alkylation of the oxazinone with [C-13]methyl iodide was achieved with high diastereoselectivity. Hydrolysis and removal of the chiral auxiliary of the alkylated oxazinone gave L-[3-C-13]alanine. Copyright (C) 2003 John Wiley Sons, Ltd.

关键词： alkenes   asymmetric amplification   asymmetric catalysis   autocatalysis   chirality  

摘要： The light touch: Asymmetric photoequilibrium and autocatalysis act as sources of homochirality in a highly enantioselective preparation of chiral alcohols (see scheme). This process is initiated by left- and right-circularly polarized light (CPL) and exploits the resulting photoequilibrium between chiral olefin substrates to yield 2-alkynyl-5-pyrimidyl alkanols.

摘要： This research has focused on the asymmetric synthesis of the natural product (−)gephyrotoxin. This product was isolated and characterized by Daly and coworkers in 1977. Kishi and co-workers published the first synthesis of (−)-gephyrotoxin in 1980, and the first synthesis of (+)-gephyrotoxin in 1981. No synthesis of (−)-gephyrotoxin has been published to date. In exploring the possibilities for the synthesis of (−)-gephyrotoxin, many synthetic transformations were investigated including, Homer-Wadsworth-Emmons, Diems-Alder, orthoester Claisen, and Mukaiyama-Michael addition. Diem-Alder and Horner-Wadsworth-Emmons Chemistry was explored for formation of the 6,6 trans ring system necessary for (−)-gephyrotoxin. Previously synthesis of only cis ring systems had been developed. Orthoester Claisen rearrangement and Mukaiyama-Michael addition were investigated to set the C6 and 5a stereocenters. Our progress toward the synthesis of (−)-gephyrotoxin yielded other developments as well. The formation of both the cis and trans 4-hydroxy-3,4-dihydro-2H-pyridines was accomplished for the first time, and the formation of 5-iodo, and 5-vinly-2,3-dihydro-4pyridones was improved.

关键词： d-生物素   手性辅助剂   不对称合成   生物碱   噁唑啉   杂环化合物  

摘要： d-生物素(d-biotin)是动物维持其正常生理机能所必需的一种水溶性B族维生素。它是具有戊酸侧链的噻吩与环脲稠合的杂环化合物，共有8种立体异构体，只有全顺式的(3aS,4S,6aR)-biotin才具有生理活性。 　　继1949年Sternbach首次开发出d-生物素的化学全合成后，各国化学家纷纷致力于d-生物素的工业全合成研究，取得了不少可喜的进展。本文第一章就此作了简要综述，重点从工业角度加以分析，指明沿仿Sternbach合成法的方向及需要解决的若干关键问题。 　　第二章针对Sternbach合成法的不足之处，作出了四个方面的改进：1)内消旋-2，3-双(苄胺基)丁二酸的关环;2)由内消旋的环酐9去对称化生成(3aS,6aR)-内酯6;3)高效简便地合成噁唑啉保护羧基的五碳侧链;4)苄基保护基的脱除。提出了以2，3-双(苄胺基)丁二酸为起始原料，经关环，脱水得环酐9，再以手性辅助剂对内消旋的环酐9去对称单酯化，选择性还原，硫代得关键中间体(3aS,6aR)-硫内酯4;在4的C4位以Grignard反应一锅法引入五碳侧链，Pd(OH)2/C立体专一性加氢还原得到双苄生物素2，再经甲磺酸脱去苄基保护得到d-生物素(1)的不对称合成新路线，总收率41.2％。 　　此外，本论文对相关反应进行了研究，通过IR，1HNMR和MS对涉及的中间体和副产物进行了结构鉴定，其中化合物7a，6及3的绝对构型经X-单晶衍射确证。

关键词： 生物催化   去消旋化   不对称合成   应用  

关键词： .piperidines   homochiral   conjugate   asymmetric synthesis   DIBAL   amino esters   aldehydes and ketones   unsaturated esters   N-benzyl   coniine   amino ketones   Preparation of Amino   amino aldehydes   Wadsworth–Emmons   methylbenzylamine   Weinreb amides  

摘要： Conjugate addition of lithium (S)-N-benzyl-N-alpha-methylbenzylamide to a range of alpha,beta-unsaturated Weinreb amides proceeds with high levels of diastereoselectivity (>95% de). The beta-amino Weinreb amide products may be transformed into beta-amino ketones via reactions with Grignard reagents, while treatment with DIBAL-H furnishes beta-amino aldehydes. Trapping of the aldehyde via Wadsworth-Emmons reaction and subsequent manipulation offers an efficient route to homochiral delta-amino acid derivatives and 2-substituted piperidines. The application of this methodology for the synthesis of (S)-coniine is demonstrated.

摘要： Catalytic Asymmetric hydroboration is a useful source of chiral amines and secondary alcohols.  The chirality of the product relies upon a new stereogenic centre being formed at the site of boron addition to the alkene reactant.  The hydroboration of aromatic alkenes always proceeds via a benzyl rhodium intermediate.  This limits the scope for investigation into regioselectivity of different substituents and heteroaromatic systems. A small library of unsymmetrical stilbene derivatives was synthesised to permit variation of the electronic character.  These were subjected to catalytic hydroboration with both achiral and enantiomerically pure rhodium catalysts to investigate the regiocontrol and enantioselectivity exhibited by different stilbene substituents.  Homo- and heteronuclear NMR, HPLC and Circular Dichroism were used to assign enantioselectivity and absolute configuration. Further work looked at the extension of the results into new and more challenging areas. Moderate to excellent regioselectivities were obtained, with up to 95% ee achieved for the major regioisomer.  The main conclusions were that it is possible to use substituents to exercise complete regiochemical control of catalytic hydroboration, but that the ligand used plays a large part in the regioselectivity.  It was also seen what effect the substituents had on ee. In addition, a new methodology was sought to obviate many synthetic limitations imposed upon hydrocarbon by its regioselectivity. A possible route to chiral organoboranes is via the synthesis of prochiral vinylboranes, followed by asymmetric hydrogenation. A vinylborane was synthesised and trial hydrogenations run with a variety of transition-metal catalysts, to screen them for their utility as hydrogenation catalysts for this system.  Yields obtained were excellent, though ee's were generally disappointing.  The use of vinylboranes as hydrogenation substrates was shown to have potential, but

关键词： Aldehydes  

摘要： A novel carbonyl alkynylation has been accomplished based on utilization of the Meerwein-Ponndorf-Verley (MPV) reaction system. The success of the MPV alkynylation crucially depends on the discovery of the remarkable ligand acceleration effect of 2,2'-biphenol. For example, the alkynylation of chloral (2c) with the aluminium alkoxide 6 (R = Ph), prepared in situ from Me3Al, 2,2'-biphenol and 2-methyl-4-phenyl-3-butyn-2-ol (1a) as an alkynyl source, proceeded smoothly in CH2Cl2 at room temperature to give the desired propargyl alcohol 3ca in almost quantitative yield after 5 h stirring. The characteristic feature of this new transformation involving no metal alkynides can be visualized by the fact that the alkynyl group bearing keto carbonyl was transferred successfully to aldehyde carbonyl without any side reactions on keto carbonyl. Although the use of (S)-1,1'-bi-2-naphthol and its simple analogues was found to be unsuitable for inducing asymmetry in this reaction, design of new chiral biphenols bearing a certain flexibility of the biphenyl axis led to satisfactory results in terms of enantioselectivity as well as reactivity.