关键词： Substituents   Iodine   Reagents   Chemical reactions   Styrenes  

摘要： The synthesis of new chiral hypervalent iodine compounds 3 and their use in asymmetric oxidative functionalizations are described. The substituents in the chiral moiety and the stereoelectronic properties of the reagents 3, as well as the reaction conditions, have been optimized. Chiral hypervalent iodine compounds 3 have been investigated in the asymmetric dioxytosylation of styrene and in the alpha-oxytosylation of propiophenone as test reactions. X-ray structural analysis of some reagents shows an interaction between the chiral moiety and the iodine resulting in stereoselectivities up to 53% ee in the products.

关键词： Redox reactions   Hydrocarbons   Alcohols   Organic compounds   Molecular structure  

摘要： The stereoselective synthesis of(-)-methyl palustramate, a possible intermediate for the synthesis of(+)-palustrine, is described. The key step of the synthesis is a conformationally restricted Claisen rearrangement to afford the highly functionalized 1-benzylpipecolic ester 10. In addition, a new procedure for debenzylation of 1-benzylpiperidines (Li, (NH2CH2)(2), Et3N, THF) was used to remove the benzyl protecting group where traditional methods failed.

关键词： Oxides   Organic reactions   Ethers   Carbonyls   Oxidation  

摘要： Focuses on the available methods used in the preparation of the alpha-heterosubstituted carbonyl compounds which involves the enantiomerically enriched form. Achievement of excellent levels of stereocontrol in the reaction of chiral enolates with heteroatomic electrophiles; How substrate dependence can be avoided; Confirmation of the stereochemistry of the generated stereocenter.

关键词： .diastereoselectivity   carboxylates   asymmetric oxidation   Monoxides   Dithiane Dioxide   CHP equiv DET   OiPr equiv   trans bis-sulfoxide   ethyl dithiane   hydrolysis and decarboxylation  

摘要： Asymmetric oxidation of a range of 1,3-dithianes was studied using the Kagan protocol [CHP (4 equiv), (+)-DET (2 equiv), Ti(OiPr)(4) (1 equiv), and H2O (1 equiv) at -35 degrees C for 48 h]. 1,3-Dithiane itself gave monoxide (30% eel and the trans bis-sulfoxide (59% eel but with low enantioselectivity. In contrast, ester derivatives (Me, Et, t-Bu, Ph) of 1,3-dithiane-2-carboxylates gave monoxides (80-95% eel and trans bis-sulfoxides (> 97% ee) in high enantioselectivity. Optimum conditions for the oxidation of ethyl 1,3-dithiane-2-carboxylate required the Modena protocol [CHP (4 equiv), (+)DET (2 equiv), and Ti(OiPr)(4) (0.5 equiv) at -22 degrees C for 24 h], and this gave the trans bis-sulfoxide in 60% yield and high enantioselectivity. The bis-sulfoxides were found to be acid sensitive and required rapid workup and purification for optimum yields. The differences between the Modena and Kagan oxidants are discussed together with a discussion on the origin of the high enantio- and diastereoselectivity of the reaction. Finally, hydrolysis and decarboxylation furnished trans-1,3-dithiane 1,3-dioxide.

关键词： Catalysts   Indoles   Chemical reactions   Organic compounds   Enantioselective synthesis  

关键词： Hydrocarbons   Alcohols   Carbohydrates   Catalysts   Metathesis  

关键词： asymmetric synthesis   hydrogen transfer   photochemistry   solid-state chemistry   topochemistry  

摘要： Due to the matrix effect of the crystal lattice, irradiation of ketone 1 yields 2 diastereoselectively as the main product (97% de). Furthermore, the chiral crystal environment in single crystals of 1 (space group P2(1)2(1)2(1)) also renders the reaction enantioselective (86% ee). Both enantiomers of alcohol 2 could be produced, depending on which enantiomorphic form of the chiral crystal was irradiated. As the ketone 1 is achiral and the chiral induction is caused exclusively by physical influences, this reaction represents a further example of an absolute asymmetric synthesis.

关键词： aldol reactions   antitumor agents   bryostatin   total synthesis  

摘要： The potent bryostatin antitumor agents are currently in phase II clinical trials for the treatment of a variety of forms of cancer. Aldol reactions and directed reductions are among the essential steps for the formation of fragments A-C in the total synthesis of the title compound. Coupling of these fragments by sulfone-based olefination and alkylation reactions was followed by macrocyclization and introduction of the enoate moieties on rings B and C.◆ (© 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

关键词： Ethers   Rearrangement   Vinyl   Stereochemistry   Cyclopropanation  

摘要： Rhodium N-(dodecylbenzenesulfonyl)prolinate [(Rh-2(S-DOSP)(4) (1)]-catalyzed decomposition of diazobutenoates in the presence of vinyl ethers results in highly diastereoselective and enantioselective synthesis of donor/acceptor-substituted vinylcyclopropanes. Diethylaluminum chloride-induced rearrangement of these vinylcyclopropanes results in the formation of cyclopentenes with excellent control of diastereoselectivity and for the fused cyclopentenes good control of absolute stereochemistry. This study illustrates the synthetic utility of Rh-2(S-DOSP)(4) as a chiral catalyst for vinylcarbenoid cyclopropanations and the remarkable diastereocontrol that is possible in the diethylaluminum chloride-induced ring expansion of donor/acceptor-substituted vinylcyclopropanes.

关键词： 不对称合成   L-焦谷氨酸   手性源   焦谷氨酸  

摘要： 简介了Ｌ－焦谷氨酸作为手性源的反应特点，综述了Ｌ－焦谷氨酸作为手性源在不对称合成中的应用。