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： 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.

关键词： LEWIS acids   STEREOCHEMISTRY  

摘要： Stereochemically well-defined homoallylic thioethers 3 are synthesized via Lewis acid promoted condensation reaction between chiral organosilane reagents 2 and in situ generated thionium ions. The stereochemical course of the reaction is consistent with earlier reports concerning crotylsilations of oxonium ions.

关键词： Chromium   Alcohols   Reaction products   Samarium   Cross coupling reaction  

摘要： [GRAPHICS] Samarium iodide mediated reductive cross-coupling of N-tosyl benzylideneamine with benzaldehydes or the corresponding chromium complexes gave syn-beta-amino alcohol derivatives. A dynamic kinetic resolution of a configurationally equilibrated reactive species occurred in the cross-coupling with planar chiral benzaldehyde chromium complexes.

关键词： Aldehydes   Peptides and proteins   Monomers   Enantioselective synthesis   Organic compounds  

摘要： [GRAPHICS] The asymmetric synthesis of the methylated tryptophan portion of hemiasterlin peptides is described. The key reactions are a SnCl4-mediated ring opening of epoxynitriles or epoxysulfones by N-methylindole followed by an asymmetric Strecker reaction. A second approach involving opening of glycidic esters by indoles is also described.