关键词： isocarbacyclin   asymmetric olefination   allylic sulfoximine   cross-coupling reaction   chiral lithium amide  

摘要： An asymmetric synthesis of isocarbacyclin (2) was achieved from ketone 7 by the olefination-isomerization-coupling process with chiral sulfoximines. The vinylic sulfoximine 6 (greater than or equal to 98% de) was prepared from ketone 7 and lithiosulfoximine 8 by an asymmetric olefination via an addition-elimination process. Model experiments, aiming at a rationalization of the asymmetric induction in the elimination of hydroxysulfoximines, with ketone 12 and lithiosulfoximine ent-8 revealed formation of the silyl ether 15 as an intermediate which eliminated LiOSiMe3 upon reaction with nBuLi under formation of (S,Z)-alkene 17 (greater than or equal to 98% de). Reaction of the C,O-dilithiosulfoximine 19 with ClSiMe3 led to elimination of LiOSiMe3 and also gave 17 (greater than or equal to 98% de). Methylation of 19, however, furnished the corresponding alpha-methyl-substituted beta-hydroxysulfoximines, 20 and 21, in a ratio of 75:25. Isomerization of sulfoximine 6 gave the allylic sulfoximine 5 (96% de) whose absolute configuration was determined by X-ray structure analysis. Cross-coupling reaction of 5 with cuprate 23 delivered with high regioselectivity alkene 25. A similar reaction of 5 with the organocopper reagent 26, which was prepared from (benzyloxy)methylmagnesium chloride, in the presence of BF3. OEt2 and halide afforded alkene 27. Ketone 28 is a potential starting material for the asymmetric synthesis of 3-oxaisocarbacyclin. Besides alkenes 25 and 27 sulfinamide 24 (97% ee), whose conversion to 8 has been already described, was isolated in 90% yield. The key step in the sequence leading to the construction of the omega-side chain was the deprotonation of ketone 4b with a complex of lithium (R,R)-bis(alpha-phenylethyl)amide and Lithium chloride, ***, which gave enolate 3. The use of *** in deprotonation of 4b afforded the isomeric enolate 30. Enolates 3 and 30 were trapped as the silyl ethers 31 (90% ie) and 32 (92% ie), respectively. The aldol r

关键词： trifluoroacetaldehyde   derivatives   Alcohols   Optical activity   Asymmetric synthesis   Derivatives  

摘要： Reaction of trifluoroacetaldehyde with an alcohol in the presence of a catalytic amount of (R)-BINOL-Ti(O-i-Pr)(2) gives optically active 1-alkoxy-2,2,2-trifluoroethanol with high ee.

关键词： Purification   Anions   Enantioselective synthesis   Organic compounds   Boron  

摘要： Highly stereoselective boronic ester chemistry has been used for the synthesis of (4S,6S,7S)-7-hydroxy-4,6-dimethylnonanone (1), the pheromone of the cigarette beetle. 2-Bromo-1-butene (8) was made from 1-butyne via bromoboration and protodeboronation, and was converted to 1-ethylethenylmagnesium bromide. (R,R)-1,2-Dicyclohexyl-1,2-ethanediol ["(R)-DICHED"] methylboronate was treated with (dichloromethyl)Lithium to yield (R)-DICHED (S)-1-chloroethylboronate (9), which with 1-ethylethenylmagnesium bromide yielded (R)-DICHED (R)-(2-ethyl-1-methyl-2-propenyl)boronate (10). Further chain extensions with (chloromethyl)lithium, (dichloromethyl)lithium followed by methylmagnesium bromide, and (dichloromethyl)lithium followed by ethylmagnesium bromide completed assembly of the carbon skeleton. Deboronation with hydrogen peroxide yielded (3S,5S,6S)-2-ethyl-3,5-dimethylocten-6-ol (14), which with osmium tetraoxide and sodium periodate yielded 1.

关键词： Alcohols   Nucleic acids   Monomers   Organic compounds   Acid and base chemistry  

关键词： Palladium   Hydrocarbons   Ligands   Stereoselectivity   Molecular structure  

摘要： The reaction of Pd-2(dba)(3) . CHCl3 with 2 equiv of chiral, C-2-symmetrical cyclopropenes bearing lactate esters at the 1- and 2-positions provided trans-5-palladatricyclo[4.***.0.0(2,4)]heptanes (PTHs) in high diastereomeric excess. The configuration of all stereocenters in the major diastereomer was determined by X-ray structure analyses of the complexes of the PTH-with norbornadiene;the C-2 symmetry of the (+)-DIOP complex of the minor diastereomer proves that this was also a trans isomer.

关键词： α-氨基酸   不对称合成   吗啉-2,5-二酮  

关键词： 手性氨基醇   不对称合成   不对称催化   氨基醇  

摘要： 综述了手性氨基醇作为配体或催化剂在不对称合成中的应用及最新进展。

关键词： D(-)樟脑磺内酰胺   手性助剂   不对称合成  

摘要： 以天然樟脑为原料，经过磺酰化、酰氯化、酰胺化、环化、还原５步反应合成了Ｄ（－）樟脑磺内酰胺（１）．本方法操作简便，反应时间短，总产率达４０９％．（１）是一种优良的手性助剂，广泛应用于不对称合成．

关键词： 季胺盐   手性胶束   不对称合成   胶束制备  

摘要： 报导了从（±）α甲基苄胺通过拆分得（－）α甲基苄胺，再经甲基化、十六烷基化，经过对不同条件的选择，合成出手性胶束ＬＮα甲基苄基Ｎ，Ｎ二甲基溴代十六烷基季胺盐．产物经ＩＲ、ＵＶ、１ＨＮＭＲ进行了表征．

关键词： C对称轴   不对称合成   有机电化学   立体选择性