关键词： asymmetric catalysis   asymmetric synthesis   metathesis   nucleosides   palladium  

摘要： Racemic butadiene and isoprene monoepoxide react with unsaturated alcohols in the presence of a chiral palladium catalyst and a boron co-catalyst to give 3-alkoxy-4-hydroxy-1-butene and 3-alkoxy-4-hydroxy-3-methyl-1-butene, respectively, with excellent regio- and enantioselectivity in a dynamic kinetic asymmetric transformation whereby both enantiomers of the starting epoxides provide the same enantiomeric product. In the case of 2-phenylbutadiene monoepoxide, easily available from phenacyl chloride and vinylmagnesium bromide, the reaction proceeds by kinetic resolution. A model to rationalize the result is presented. The bis-olefin products are ideal substrates for the Ru catalyzed ring closing metathesis. In this way, five-, six-, and seven-membered oxygen heterocycles are readily available enantiomerically pure. The value of this very simple two step process is demonstrated by the use of the five-membered ring heterocycles to form unnatural and unusual nucleosides that cannot be easily accessed by other means. The sequence involves a Ru catalyzed isomerization of the initial 2,5-dihydrofuran to a 2,3-dihydrofuran followed by a selenium promoted addition of a pyrimidine or purine base. One advantage of this strategy is the easy access to either enantiomeric series, both of which have important biological applications.

关键词： ASYMMETRIC synthesis   AMINO acids   IMINES  

摘要： The enantiopure Davis' N-sulfinylimines were found to be efficient as chiral imine equivalents in the high-temperature Reformatsky-type additions with BrZnCF2COOEt affording an efficient approach to the enantiomerically pure alpha,alpha-difluoro-beta-amino acids. High chemical and stereochemical yields (drs > 9:1, and as high as 99:1) render this method immediately useful for preparing the target amino acids.

关键词： Phosphonates   Asymmetric synthesis  

摘要： The addition of potassium dialkyl phosphites to enantiopure O-protected alpha-hydroxy sulfinimine pseudoenantiomers affords beta-hydroxy alpha-amino phosphonates in good yield and de. The reaction exhibits a strong match-mismatch effect.

关键词： ASYMMETRIC synthesis   ENANTIOMERS   ALKENES  

摘要： A short and efficient enantioselective synthesis of both enantiomers of anti-4,4,4-trifluorothreonine and 2-amino-4,4,4-trifluorobutanoic acid was successfully developed. Trifluoromethylation of benzyl-protected bromoalkene 4 provided key intermediate trifluoromethylated transdisubstituted alkene 2 in good yield. The sequence then involved Sharpless asymmetric dihydroxylation, nucleophilic opening of cyclic sulfate with NaN3, palladium-catalyzed selective hydrogenation, and oxidation.

关键词： Palladium   Organic compounds   Functional groups   Ligands   Genetics  

摘要： The asymmetric syntheses of ester- and thionoester-substituted P-stereogenic phosphines have been achieved between 3,4-dimethyl-1-phenylphosphole (DMPP) and dieneophiles, methyl acrylate and o-ethyl-(E)-2-butenethioate, respectively, in the presence of the enantiomerically pure ortho-palladated (1-(dimethylamino)ethyl)naphthalene as the chiral template. The exo and endo reaction pathways could be controlled stereoselectively by manipulating the number of accessible coordination sites on the chiral palladium template. Both methyl acrylate and o-ethyl-(E)-2-butenethioate underwent intramolecular exo-cycloaddition on the palladium template to form the corresponding P-stereogenic exo-phosphanorbornenes as P-O and P-S bidentate chelates, respectively. When the ester-substituted P-O bidentate template complex was treated with an aqueous solution of sodium chloride under mild reaction conditions, the Pd-O bond was displaced chemoselectively by the chloride ion, but the phosphanorbornene remained coordinated on palladium as a monodentate ligand via its phosphorus donor atom. A similar aqueous treatment of the thionoester-substituted P-S bidentate did not cleave the Pd-S bond but resulted in the rapid hydrolysis of the C(S)-OEt bond to give a new thioester P-S metal chelate. In the intermolecular endo-cycloaddition pathway, only methyl acrylate coupled with DMPP to give a pair of separable ester-substituted endo-cycloadducts. The thionoester-substituted dienophile o-ethyl-(E)-2-butenethioate was not reactive toward the endo-cycloaddition reaction.

关键词： LIPASES   PIPERAZINE   ENANTIOMERS  

摘要： Lipase TL-mediated kinetic resolution of (+/-)-5-benzyloxy-1-tert-butyldimethylsilyloxy-2-pentanol (5) at low temperature proceeded to give the corresponding (S)-alcohol 5 and (R)-acetate 6 in quantitative yields with high enantiomeric purity. The addition of bases such as pyridine, DMAP, 2,4- and 2,6-lutidines, or triethylamine considerably enhanced the rate of kinetic resolution. The alcohol (S)-5 and the acetate (R)-6 were converted to piperazic acid derivatives (R)- and (S)-3, respectively, via the intramolecular Mitsunobu reaction as a key step.

关键词： GLYCINE   AMINO acids   PROLINE   NUCLEOPHILIC reactions  

摘要： A synthetically practical and operationally convenient method for preparing (S)-2-[N-(N-benzylprolyl)-amino] benzophenone (BPBP) and hitherto unknown (S)-2-[N-(N'-benzylprolyl)amino]-4-methylbenzophenone (4-MeBPBP), (S)-2-[N-(N'-benzylprolyl)amino]-5-nitrobenzophenone (5-NO2-BPBP), and their corresponding Ni(II) complexes with glycine [GlyNi(II)BPBP], a widely used chiral equivalent of nucleophilic glycine, and new analogues [GlyNi(II)4-Me-BPBP] and [GlyNi(II)-5- NO2-BPBP] is described. The key step of the method is the synthetically efficient amid bond formation between the corresponding o-aminobenzophenones, featuring significant steric shielding and low nucleophilicity of the amino functionality as well as sterically constrained (S)-N-benzylproline (BP).

关键词： DARZENS reaction   PHOSPHONATES   ENANTIOMERS  

摘要： The aza-Darzens reaction of lithium diethyl iodomethylphosphonate with enantiopure N-(2,4,6-trimethylphenylsulfinyl)imines affords a single diastereomeric N-sulfinylaziridine 2-phosphonate which, on treatment with MeMgBr, gives the corresponding NH-aziridine 2-phosphonate chiral building blocks. An improved asymmetric synthesis of (S)-(+)-2,4,6-trimethylphenylsulfinamide is also given.

关键词： 面包酵母   不对称合成   还原反应   生物催化   化学反应  

摘要： 总结了近期面包酵母在不对称合成中的应用进展 。

关键词： macroscopic chirality   absolute asymmetric synthesis   homochirality   physical fields  

摘要： The paper introduces the concept of using three independent, macroscopic factors affecting mutual orientation of the reactant molecules to accomplish absolute asymmetric synthesis. Unlike with other methodologies of asymmetric synthesis in physical fields, none of the utilized factors is chiral in itself (as, e.g., circularly polarized light would be), but the combination of the three constitutes a macroscopically chiral influence. Examples of applicable directional factors are time-even vector fields (e.g., electric field and the directional effects of surfaces and interfaces) and the time-odd directional transport with encounter control. The directional factors employed may act simultaneously or, if their effect can be preserved, consecutively, thus allowing, e.g., a repeat use of the electric field. The electric field strength needed to achieve a practically useful degree of molecular orientation was estimated to be ca. 3 MV/cm, which is now commonly achieved with organic materials in the area of nonlinear optics. Practical implications are discussed, as well as the implications for the origins of natural homochirality.