关键词： Nitrogen compounds   Cyclization   Stereoselectivity   Enantioselective synthesis   Molecular structure  

摘要： [GRAPHICS] A highly diastereoselective intramolecular nitrone cycloaddition onto a chiral ketene equivalent, obtained by Horner-Wadsworth-Emmons olefination of either enantiomer of bis-sulfinyl phosphonate 6, is described. Cycloaddition gave 5,5-disubstituted isoxazolidine 10 in good yield as a single diastereomer. Catalytic hydrogenolysis of 10 furnished either enantiomer of optically pure cis-2-aminocyclopentane-1-carboxylic acid.

关键词： (2S,3R)-1,2,3-丁三醇-1-对甲苯磺酸酯   手性邻二醇   对映选择性开环   不对称合成  

摘要： 以 (E) 2 丁烯 1 醇为原料经不对称环氧化反应合成 2 ,3 环氧醇 (1)。该环氧醇的对甲苯磺酸酯对映选择性酸水解开环制备手性邻二醇 (2 ) (95 %ee)

关键词： α-取代膦酸   α-取代次膦酸   不对称合成   Baylis-Hillman反应   重结晶方法   手性膦酸酯化合物  

摘要： 通过重结晶方法得到了两个具有光学纯的α-羟基次膦酸的单晶,对它们进行了X光衍射晶体结构分析并确定了其中一个的绝对构型.在Baylis-Hillman反应中,针对反应速度慢、转化率低等明显的缺点,选用便宜易得的Me<,3>N·H<,2>O作催化剂,在水存在的均相体系中实现了反应速度大提高、反应条件温和、操作简便且有很好的收率.同时,还研究了DABCO、DMAP、乌落托品等催化剂在水存在下的均相体系中对Baylis-Hillman反应的催化效果,并探讨了温度、溶剂、微波对反应速度和转化率的影响.在Me<,3>N·H<,2>O催化下用丙烯酸薄荷醇酯诱导不对称Baylis-Hillman反应,获得了很好的不对称诱导效果.合成了一些手性膦酸酯化合物,使之和TiCl<,4>共同催化Baylis-Hillman反应,得到了氯代Baylis-Hillman反应产物,反应的不对称诱导效果较差.

关键词： 不对称合成   手性磷配体   催化剂   研究进展   配体催化   手性氧化膦   手性磷酰胺   手性磷酰胺酯   手性磷酸三酯  

摘要： 评述了作为配体催化剂的手性三配位及四配位磷化合物的合成及其在某些不对称合成反应中的应用

关键词： Carboxylic Acids   Catalysis   Cinchona Alkaloids   Dioxolanes   Kinetics   Support   Non-U.S. Gov't   Support   U.S. Gov't   P.H.S.  

摘要： A highly enantioselective catalytic transformation of racemic alpha-hydroxy acids to optically active alpha-hydroxy acids is reported. A new procedure was developed for the condensation of racemic alpha-hydroxy acids with trichloromethyl chloroformate (diphosgene) at room temperature in the presence of activated charcoal to form 5-substituted-1,3-dioxolane-2,4-diones in 90-100% yield. An efficient dynamic kinetic resolution of 5-aryl dioxolanediones was realized via a modified cinchona alkaloid-catalyzed alcoholytic opening of the dioxolanedione ring, generating a variety of optically active alpha-hydroxy esters in 91-96% ee and 61-85% chemical yield. In this dynamic kinetic resolution, the modified cinchona alkaloid was found to serve dual catalytic roles, mediating both the rapid racemization of the 5-aryl dioxolanediones and the enantioselective alcoholytic ring opening of the 5-aryl dioxolanediones. Consequently, both enantiomers of the 5-aryl dioxolanediones were converted to highly enantiomerically enriched aromatic alpha-hydroxy esters in yields (61-85%), far exceeding the maximum of 50% for a normal kinetic resolution. This development not only represents an expansion of the scope of asymmetric acyl-transfer catalysis of synthetic catalysts but also provides a new approach for the development of efficient chemical dynamic kinetic resolutions promoted by a single catalyst. 5-Alkyl dioxolanediones were resolved by a conventional but highly enantioselective kinetic resolution to provide alpha-hydroxy acids and esters in high optical purity and good yields.

关键词： .asymmetric induction   asymmetric synthesis   chiral inductor   optically   pseudoephedrine  

摘要： Three different approaches to asymmetric induction in the cis-to-trans photoisomerization of a number of 1-benzoyl-2,3-diphenylcyclopropane derivatives are reported: the use of chiral inductors and covalent chiral auxiliaries in MY zeolites and the use of ionic chiral auxiliaries in crystals. High levels of asymmetric induction were achieved using the latter two methods-up to 71% through the use of covalent chiral auxiliaries in zeolites and a remarkable 99% via the solid state ionic chiral auxiliary approach. In the zeolite method, the diastereomeric excess was found to depend strongly on the nature of the zeolite cation, M(+), and in the ionic chiral auxiliary approach, evidence is presented that it is the fixed orientation of the benzoyl group with respect to the cyclopropane ring that controls enantioselectivity in the crystalline state-a finding that is directly relevant to theoretical work on this topic.

关键词： CHEMICAL models   CARBON  

摘要： Metal-mediated 1,3-butadien-2-ylation reactions between 1,4-dibromo-2-butyne or 1,4-bis(methanesulfonyl)-2-butyne and optically pure azetidine-2,3-diones were investigated in aqueous media, offering a convenient asymmetric entry to the potentially bioactive 3-substituted 3-hydroxy-beta-lactam moiety. The diastereoselectivity of the addition reaction was controlled by the bulky chiral auxiliary at C4. However, while the regioselectivity of the process was full, the chemical yield of the addition was a function of the nature of both the metal reagent and the system solvent as well. In addition, 2-azetidinone-tethered 1,3-butadienes can easily be transformed into other functionalities via Diels-Alder reaction.

关键词： ENANTIOMERS   BENZAMIDE   STRUCTURE-activity relationships (Biochemistry)  

摘要： Axially chiral benzamides and anilides were prepared by enantiotopic lithiation at the distinguished benzylic methyl of prochiral tricarbonylchromium complexes of N,N-diethyl 2,6-dimethylbenzamide (1) and N-methyl-N-acyl 2,6-dimethylaniline (14 and 21) with a chiral lithium amide base followed by electrophilic substitution in good yields with high optical purity. The resulting axially chiral chromium-complexed benzamides and anilides were oxidized under air to give chromium-free axially chiral benzamides and anilides in an enantiomerically active form without axial bond rotation at room temperature.

关键词： Alcohols   Anions   Aldehydes   Oxidation   Aldol reactions  

摘要： [GRAPHICS] A biosynthetic proposal for ring formation in the antitumor agent halichomycin is presented in which macrocyclization of the putative prehalichomycin intermediate 1 is the first step. Compound 2 then undergoes dehydration to the alpha-keto N-acylimine 3 followed by tandem nucleophilic addition of the C(16)-hydroxyl to form the hemimacrolactam. A stereospecific Michael ring closure and enol protonation complete C-ring assembly. So far, synthetic efforts toward 1 have resulted in 8.

关键词： asymmetric synthesis   crystallization-driven transformation   dihydroxylation   Mitsunobu reaction   substance P inhibitors  

摘要： A novel three-component condensation followed by a crystallization-induced asymmetric transformation is used to build this key substance P inhibitor intermediate in a short synthetic sequence.