关键词： Sulfur compounds  

摘要： Intramolecular 1,3-dipolar nitrone cycloaddition onto an enantiomerically pure ketene dithioacetal dioxide using a three-carbon tether gave the corresponding 5,5-disubstituted isoxazolidine as a single diastereomer in good yield. This reaction has been used as the key step in an asymmetric synthesis of the naturally occurring antibiotic, (-)-cispentacin. An asymmetric synthesis-of 4-amino-pyrrolidine-3-carboxylic acid has also been carried out using the intramolecular nitrone cycloaddition as the stereocontrolling step.

关键词： CHIRALITY   CRYSTALLIZATION  

摘要： Asymmetric synthesis using frozen chirality generated by spontaneous crystallization was performed. Achiral asymmetrically substituted imide with a tetrahydronaphthyl group on the nitrogen atom crystallized in a chiral fashion, with space group P2(1)2(1)2(1). The molecular chirality generated by spontaneous crystallization was retained in cold THF. The half-life determined on the basis of decreasing optical activity followed by CD spectrometer was 7.8, 33.1, and 150.0 min at -20, -30, -40 degreesC, respectively. The energy barrier (DeltaG*) of racemization was calculated with the temperature dependence of the kinetic constant to be 18.24-18.36 kcal mol(-1) at 233-253 K. The memorized frozen chirality was transferred to permanent optically active alcohols by nucleophilic addition with n-buthyllithium.

关键词： XANTHENE   PHORBOL esters  

摘要： An asymmetric synthesis of aza analogues of the ABC ring system of phorbol and related compounds containing the 5-7-6-fused framework of daphnane involved construction of the central seven-membered ring by a regioselective reduction of a chiral imide and cyclization with trifluoromethanesulfonic acid. Subsequent demethylation and oxidative dearomatization of ring C afforded an enantiopure dienone 20 with the same relative and absolute configuration at the 9- and 10-positions of the phorbol skeleton.

关键词： Diols   Protective groups   Organic compounds   Reactivity   Post-translational modification  

摘要： A new route, of potential strategic importance, to a difluorosugar analogue has been developed. Key steps included a Stille coupling and a highly regio- and enantioselective dihydroxylation of a highly substituted diene. Protecting groups were chosen to enhance the reactivity of the disubstituted allylic fragment in the AD reaction and allow deprotection under orthogonal conditions.

关键词： Isolation   Chemical structure   Organic compounds   Molecular structure   Selectivity  

摘要： [GRAPHICS] A short asymmetric synthesis of (2'S,5R,6R)-2'-[6-amino-5-hydroxy-1,3-cyclohexadiene-1-carbonyloxy]propionic acid, the enantiomer of the reported structure of (+)-oryzoxymycin is described. The reported spectral data does not match that obtained for synthetic "oryzoxymycin".

关键词： 手性双噁唑啉金属配合物   催化合成   不对称合成   Lewis酸催化剂   有机合成  

摘要： 在简要介绍各种结构类型的手性双噁唑啉配体的基础上,总结了近期手性双噁唑啉金属配合物在不对称合成中的应用。

关键词： 光学活性   含硅氨基酸   不饱和氨基酸   不对称合成   丙氨酸   苯丙氨酸   肺氨酸  

摘要： 光学纯的硅取代氨基酸是一类非天然的手性氨基酸合成子 ,在药物、植物保护剂和精细化学品的合成中具有极为广阔的应用前景 .其合成方法包括化学不对称合成及化学合成外消旋体 -生物学拆分两种 。

关键词： 光活性   1,1′-联二萘酚   动力学拆分   氧化偶合   不对称合成  

摘要： 筛选出两种较好的 1,1′ 联二萘酚拆分剂L TAC TMEDA(收率 75 % ,86%ee)和L PAC(酒石酸 ) TMEDA(收率 67% ,71%ee) .同时以L PAC(脯氨酸 )、TMEDA和CuCl的配合物PTCu为催化剂 ,在空气中催化剂量为 1.5mol%时 ,用氧化偶合方法不对称合成了光活性联二萘酚 ,收率 70 % ,35 %ee ,且回收的催化剂不需活化 ,可直接重复使用 .

关键词： 手性金属络合物催化剂   不对称合成   应用   硅氢化反应   二烷基锌   醛   烷基化反应  

摘要： 不对称合成是当前有机合成中热门研究领域,利用手性金属络合物催化剂催化不对称硅氢化、烷基化,以烯烃、酮、亚胺、醛等合成手性醇、手性胺、手性酮等具有很好的工业应用前景。本文论述了手性金属络合物催化剂在不对称硅氢化反应及其在二烷基锌对醛的不对称烷基化反应中的应用。

关键词： asymmetric synthesis   amino acids   helical structures  

摘要： We report a synthesis of a protected derivative of trans-4-aminopiperidine-3-carboxylic acid (ANC). The route provides either enantiomer. All intermediates are purified by crystallization, and large-scale preparation is therefore possible. An analogous route provides either enantiomer of trans-2-aminocyclohexanecarboxylic acid (ACHC). We have previously shown that beta-peptide oligomers containing ACHC adopt a helical conformation defined by 14-membered C = 0(i)...H-N(i - 2) hydrogen bonds ("14-helix"). Here we show that APiC residues can be incorporated into the 14-helix.