关键词： CYCLIC compounds   ASYMMETRIC synthesis  

摘要： Asymmetric synthesis of a trichothecane analogue, 4-deoxyverrucarol (2), was carried out through two types of ring expansion reactions. First, synthesis of the racemate of 2 was investigated. Thus, 1-[1-(tert-butyldimethylsiloxy)-ethyl]-1-methoxycarbonyl-2-hexen-4-one (10), prepared by Diels-Alder reaction, was converted into the cyclopropylidene 15. The cyclobutanone (+/-)-18 was obtained from 15 via dihydroxylation, followed by successive treatments with SO2CI2 in the presence of imidazole and Florisil. After transformation of (+/-)-18 into the vinylcyclobutanol (+/-)-19, the second ring expansion reaction was performed with Pd(OAc)(2) to provide the cyclopentanone (+/-)-20. The product was converted into the racemate of 4-deoxyverrucarol (2) through the cyclohexenone (+/-)22, but the diastereoselectivity during the introduction of the double bond was unsatisfactory. The selectivity was improved in the case of the asymmetric synthesis. The optically active cyclobutanone (+/-)-18 was prepared via AD reaction of 15 with 73% ee. After the transformation of (+/-)-18 into the cyclohexanone (-)-30 through the palladium-mediated ring expansion reaction, (-)-30 was subjected to the diastereoselective deprotonation reaction using the chiral amide. The key synthetic intermediate (-)-25 of 4-deoxyverrucarol (2) was synthesized in an optically pure form by taking advantage of a kind of kinetic resolution that occurred during the deprotonation step.

关键词： Organic-synthesis   Derivatives   Oxidation   Acid   Mild  

摘要： Focuses on the asymmetric characterization of (+)-dihydrokawain-5-ol from the extracts of the kava plant, Piper methysticum. Yield of the axial alcohol and the equatorial alcohol; Cis relationship due to the H-5 equatorial hydrogen and the H-6 axial hydrogen; Corresponding sulfinyl and sulfonyl derivatives.

关键词： AMINO acid synthesis   IMINES   ADDITION reactions  

摘要： The first asymmetric synthesis of cr-amino acids based on diastereoselective carbon radical addition to glyoxylic imine derivatives is reported. The addition of an isopropyl radical, generated from i-PrI, Bu3SnH, and Et3B in CH2Cl2 at 25 degrees C, to achiral glyoxylic oxime ether 1 proceeded regioselectively at the imino carbon atom of the oxime ether group to give an excellent yield of the C-isopropylated product 2. The competitive reaction using glyoxylic oxime ether 1 and aldoxime ether 4 showed that the reactivity of the glyoxylic oxime ether toward nucleophilic carbon radicals was enhanced by the presence of a neighboring electron-withdrawing substituent. Thus, the alkyl radical addition to glyoxylic oxime ether 1 proceeded smoothly even at -78 degrees C, in contrast to the unactivated aldoxime ether 4. A high degree of stereocontrol in the carbon radical addition to the glyoxylic oxime ether was achieved by using Oppolzer's camphorsultam as a chiral auxiliary. The stannyl radical-mediated reaction of the camphorsultam derivative 6 with an isopropyl radical at -78 degrees C afforded a 96:4 diastereomeric mixture, 7a, of the C-isopropylated product. The reductive removal of the benzyloxy group of the major diastereomer (R)-7a, by treatment with Mo(CO)(6) and the subsequent removal of the sultam auxiliary by standard hydrolysis, afforded the enantiomerically pure D-valine (R)-12 without any loss of stereochemical purity. To evaluate the new methodology, a variety of alkyl radicals were employed in the addition reaction which gave the alkylated products 7 with excellent diastereoselectivity, allowing access to a wide range of enantiomerically pure natural and unnatural a-amino acids. Even in the absence of Bu3SnH, treatment of 6 with alkyl iodide and Et3B at 20 degrees C gave the C-alkylated products 7 with moderate diastereoselectivities. The use of Et2Zn as a radical initiator, instead of Et3B, was also effective for the radical reaction. The enantioselective i

关键词： 类生物碱   不对称合成  

摘要： 该论文从手性氨基酸出发,利用天然手性氨基酸为手性源,对Pyrrolidine,Pyrrolizidine以及Indolizidine等类生物碱的分子进行不对称合成研究

关键词： 不对称活化   催化反应   不对称合成   手性催化剂  

摘要： 介绍了催化不对称催化反应中的一个新概念一不对称活化(asymmetric activation)及其研究的最新进展。运用不对称活化策略,一个光学活性的或者甚至外消旋的催化剂可以被另一种手性活化剂(chiral activator)选择性地活化,从而催化反应生成非外消旋产物。该方法较不对称去活化(asymmetric deactivation)方法的优点是被活化的催化剂能够产生较使用光学纯催化剂更高对映体过量的产物。

关键词： 萘普生   不对称合成   非甾体消炎药  

摘要： 萘普生[(S)-(+)-2-(6 ＇-甲氧基一2 ＇-萘基)丙酸]是一种非常重要的非甾体消炎镇痛药.以(2R,3R)-酒石酸二甲酯为手性辅助剂,2-甲氧基萘经溴代、丙酰化、缩酮化、不对称溴化、水解、立体专一性重排和催化氢转移氢解等反应合成了光学活性萘普生,化学收率44%.制备的萘普生的光学纯度([α]_D^(25)=+63.5°)符合中华人民共和国药典(1995年版)的要求.

关键词： 不对称合成   烷基锌   醛   不对称加成反应  

摘要： 总结了烷基锌对醛的不对称加成中手性杂环配体的结构与催化活性的关系,并讨论了若干影响配体催化活性的因素。

关键词： 二茂铁   Schiff碱   不对称合成   结构表征  

摘要： Staring from ferrocene,we conveniently synthesized a series of chiral mono,di ferrocenyl schiff bases in ambient *** optical yields were *** their structures were confirmed by IR, 1H NMR,and Elemental *** *** discussed the effect of the stuctures of bases on the reactions.

关键词： 呋喃酮   合成   不对称合成   Michael加成反应  

摘要： 研究了新的手性试剂,5-(l-氧基)-3-溴-2(5H)-呋喃酮(5a)的合成及其与亲核性醇发生的串联不对称双Michael加成/分子内亲核取代反应。通过此反应,一举生成了四个新的手性中心,得到了一般方法难以合成的含有多个手性中心的丁内酯并螺-环丙烷类化合物8a～8d。详细报道了8a～8d的合成方法以及它们的[α]、IR、UV、~1H NMR、^(13)C NMR、MS、元素分析等结构分析数据。此不对称双Michael加成/分子内亲核取代反应可以为某些新的光学活性螺-环丙烷类化合物以及某些复杂结构的分子提供重要的合成策略。

关键词： 手性磷化合物   辅助剂   不对称合成   立体选择性  

摘要： 综述了手性磷化合物作为辅助剂在不对称合成中的应用.