关键词： organic chemistry   Fields   acids   Natural products   isoquinoline alkaloids   alkaloids   1,2,3,4-tetrahydroisoquinoline   Asymmetric synthesis  

摘要： Isoquinoline alkaloids are a small group of natural products with widespread occurrence in nature and also playing a very important role in the secondary metabolism of numerous vegetal families. In this context, during the last years the stereoselective synthesis of differently substituted tetrahydroisoquinolines has been a field of increasing interest in synthetic organic chemistry in which many research groups have focused much of their efforts. On the other hand, enantiopure alpha-amino acids and their derivatives have shown to be excellent tools for the organic chemist working in the field of asymmetric synthesis, either acting as chiral building blocks, auxiliaries or ligands. In this review, the different approaches for the asymmetric synthesis of substituted tetrahydroisoquinolines reported during the last years, in which chiral nonracemic alpha-amino acids or derivatives have played a crucial role will be presented. We have limited to the general procedures developed for the introduction of the desired substituents at the different positions of the tetrahydroisoquinoline core in a stereocontrolled way. However, some cases in which the obtained heterocycles have additionally been used as key synthetic intermediates for the easy preparation of other, naturally occurring, more elaborated, isoquinoline alkaloids have been covered.

关键词： amino nitriles   asymmetric synthesis   lactones   natural products   polyketides  

摘要： An efficient and straightforward ten-step asymmetric synthesis of the polyketide tarchonanthuslactone (1) in good overall yield (21% starting from chloro lactone 5) and with excellent diastereomeric and enantiomeric excesses (de, ee greater than or equal to 96%) is described. The new synthetic route is based on the alpha,beta-unsaturated delta-lactone building block 5, available in enantiopure form (ee > 99%) through an enzymatic procedure, and its conversion into methyl ketone 11 by an Umpo-lung strategy. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 2003).

关键词： asymmetric synthesis   amino acids   natural products   Stille coupling   protecting groups  

摘要： (S)-(-)-Acromelobic acid (1) was synthesized in nine steps in enantiomerically pure form from citrazinic acid (4) in an overall yield of 21 %. The key steps of this synthesis are the introduction of the amino function by the bis(lactim) ether method and the introduction of the acid function by Stille coupling. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 2003).

关键词： molecules   Sufficient   Autocatalysis   racemic mixture   Asymmetric synthesis  

摘要： Experiments were carried out to investigate whether the Soai asymmetric autocatalysis can accomplish true absolute asymmetric synthesis. In 54 reactions, R and S enantiomeric products were obtained 27 times each. Of 25 pairs of side-by-side identical reactions, 12 afforded opposite enantiomers. In a test of the mechanistic viability of a random-chance process, it was found that a very few molecules (approximately 60 000) were sufficient to control the enantiomeric outcome of these reactions. These observations appear most consistent with asymmetric synthesis originating from the chance enantiomeric excess in a racemate.

关键词： Alcohols   Antagonists   Chromatography   Enantioselective synthesis   Ethers  

摘要： A highly efficient and practical synthesis of 4,4-Disubstituted-2-Imidazolidinones utilizing a "self-reproduction of the center of chirality" strategy is described.

关键词： Alcohols   Organic synthesis   Anions   Alkyls   Stereoselectivity  

摘要： A flexible asymmetric approach to 5-alkyl tetramic acid derivatives is described, which is based on the use of 9 as the first synthetic equivalent to chiral nonracemic tetramic acid 5-carbanionic synthon 9b. The existence of the carbanion intermediate 9b was proven by trapping with trimethylchlorosilane. Application of the present method to the synthesis of antifungal alkaloid (+)-preussin, as well as protected (3S,4S)-AHPPA 6, is also described.

关键词： Carbonates   aldehydes   Cyanohydrins   ligands   Asymmetric synthesis   disalicylaldehyde ethylenediamine   Catalysis  

摘要： The bimetallic titanium complex [(salen)TiO](2), where salen is the ligand derived from (R,R)-cyclohexanediamine and 3,5-di-tert-butyl-salicylaldehyde, has been shown to catalyze the asymmetric addition of ethyl cyanoformate to aldehydes leading to cyanohydrin carbonates with high enantiomeric excesses.

关键词： 含氟α-氨基膦酸酯   合成   TMV   X-射线晶体衍射   不对称合成   不饱和酸   杂环   酰胺   酰基硫脲   生物活性   肟酯   2,3,4-三甲氧基苯乙酮  

摘要： 1含氟α-氨基膦酸酯的合成和生物活性研究;为了寻找具有高生物活性和低毒的新化合物,作者采用类Mannich反应一锅法合成一系列含氟α-氨基膦酸酯共22个,结构经元素分析、IR、1H NMR及质谱确认.所有化合物进行抗烟草花叶病毒(TMV)田间试验,结果表明部分化合物具有一定的抗TMV活性,分子中引进特异生物活性F原子有利于生物活性的提高,改变R1、R2取代基有可能筛选出更高效化合物.在化合物中,4b(R<,1>=o-F,R<,2>=p-CF<,3>,R=i-Pr)活性最高,在浓度为5×10<\'-4>%防效达84.92%.在催化剂(C<,2>H<,5>)<,2>OBF<,3>作用下,通过手性亚胺与磷酸酯立体选择性加成合成光学活性α-氨基膦酸酯.2不饱和烯酸杂环衍生物的合成与生物活性研究;在课题的研究过程中,对含不饱和键的长碳链多元烯酸杂环衍生物的合成方法进行了摸索,克服了长碳链多元不饱和烯酸双键易氧化,反应复杂,副产物较多且不易分离的困难,探索出了一条切实可行的合成路线和分离方法,为下步的深入工作打下了良好的基础.此外,对目标化合物的进行了生物活性测试并对其作用机制进行了初步探讨,测试结果表明对贵州特色中草药病害半夏枯萎病、太子参轮纹病有一定的抑制活性,其作用机制可能是作为一种植物诱导剂,通过诱导或活化植物防卫反应基因的表达体现出活性,为进一步的研究和筛选奠定了基础.另外部分新化合物的生物活性还在进一步研究当中.3 2,3,4-三甲氧基苯乙酮及其α-取代衍生物肟羧酸酯的合成和生物活性研究;从贵州地产林化工产品焦性没食子酸出发,经过一系列反应,合成了2,3,4-三甲氧基苯乙酮及其α-溴代物,再与巯基杂环反应得到杂环基硫基三甲氧基苯乙酮,随后与羟胺盐酸盐缩合得到肟,最后与酰氯反应得到肟酯.所有化合物结构经过了红外光谱、核磁氢谱分析和元素分析测试确定.在课题的研究过程中,对α-杂环苯乙酮及其肟酯衍生物的合成方法进行了探索,并取得了较理想的结果,为下步的深入工作打下了良好的基础.目标化合物的生物活性测试正在进行之中.

关键词： allylboration   asymmetric catalysis   boronic esters   chromium complex   dihydropyrans   hetero-Diels-Alder  

摘要： [4 + 2] Cycloaddition of (E)-3-borylacrolein 1 with ethyl vinyl ether, catalysed by chromium complex (1R,2S) or (1S,2R) 2, led to the corresponding cycloadducts with high diastereo- and enantioselectivities. Further reaction with aldehydes offers an attractive asymmetric route to synthetically useful substituted 3,4-dihydro-2H-pyrans.

关键词： sultones   asymmetric synthesis   chiral auxiliaries   sulfonates   one-pot reaction   cyclization  

摘要： The first auxiliary controlled asymmetric synthesis of enantiopure alpha,gamma-substituted (gamma-sultones via alpha-allylation of lithiated sulfonates by using 1,2:5,6-di-O-isopropylidene-alpha-D-allofuranose as chiral auxiliary is described. The high asymmetric inductions of the alpha-allylations were reached in good to excellent yields. Successive epimerization-free cleavage of the auxiliary and diastereoselective ring closure of the sulfonic acid intermediates in a one-pot procedure led to the title compounds in good to excellent yields and diastereo- and enantiomeric excesses (de, ee greater than or equal to 98%). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).