The asymmetric copper-catalyzed generation and subsequent [2,3]-sigmatropic rearrangement of sulfur ylides is strongly dependent on the structure of the starting allyl sulfide. A series of alkyl and aryl substituted allyl sulfides (2a-i) were reacted with ethyl diazoacetate in the presence of copper triflate (CuOTf) and a C2-symmetric bis-oxazoline ligand (5a-c). The degree of asymmetric induction ranged from 2.8% for allyl methyl sulfide (2a) to 60% for (1S,2S,5R)-(+)-allyl menthyl sulfide (2d). The enantioselectivity of the reactions was also dependent on the electronic nature of the sulfide; allyl phenyl sulfide (2e) gave a 14% ee, whereas allyl p-methoxyphenyl sulfide (2i) produced only an 8% ee. The stereochemistry of 2d and (1R,2S,5R)-(+)-allyl menthyl sulfide (7) was assigned on the basis of NMR spectroscopic experiments. 相似文献
Dialkylzinc and trialkylaluminium reagents undergo conjugate addition to alkylidene malonates with 0.5% copper triflate as catalyst. The reaction could be made enantioselective by completing the reaction in the presence of 0.5–1.0 mol% of chiral phosphorus ligand. Enantiomeric excesses (e.e.s) of up to 73% could be attained with a ligand prepared from TADDOL and 2-naphthylcyclohexanol. 相似文献
The Ti(IV)/(R)-BINOL catalyzed aldol condensation of trimethylsilyloxydiene, deriving from 2,2,6-trimethyl-4H-[1,3]-dioxin-4-one, is shown to proceed through an auto-inductive process with amplification of enantiomeric excess (e.e.). 相似文献
Enantioselective catalytic trimethylsilylcyanations of aldehydes with 48% to 92% e.e. have been studied using the novel Ti-chiral Schiff base complexes. We have found that the catalyst led to high enantoselectivity when the molar ratio of the Schiff base 1 to Ti(O-i-Pr)4 was 2:1. 相似文献
A simple and effective procedure for the enantioselective synthesis of (R)-and (S)-moprolol was described.The key step was the asymmetric synthesis of enantiopure (R)-and (S)-guaifenesin,which were synthesized from enantioenriched (R)-3-chloro-1,2-propanediol and (S)-epichlorohydrin via kinetics of hydrolysis resolution of racemic epichlorohydrin by chiral Salen-CoIIII complex.The e.e.values of both the optical compounds were above 98%,and the chemical structures of the target compounds were confirmed by 1H NMR,13C NMR,IR,and MS. 相似文献
Chiral acylnitroso dienophiles 14 , which were obtained from L -proline and from D -mandelic acid, reacted with cyclohexa-1,3-diene to give the expected diastereoisomers 15 and 16 (Scheme 2 and Table 1). The d.e. values for these Diels-Alder reactions were moderate; they are related to the molecular stiffness of the dienophiles. The absolute configuration of the major cycloadducts was interpreted in terms of HOMO/LUMO interactions, the approach being ‘endo’ and the acylintroso dienophiles reacting from their s-cis-conformation. 相似文献
In this work, we describe the direct covalent attachment of protein recognition elements (biotin) with the carboxyl groups present on the walls of polyimide nanochannels. Subsequently, these biotinylated channels were used for the bio‐specific sensing of protein analytes. Moreover, surface charge of these asymmetric nanochannels was reversed from negative to positive via the conversion of carboxyl groups into terminated amino groups. The negatively charge (carboxylated) and positively charged (aminated) channels were further used for the electrochemical sensing of bovine serum albumin (BSA, pI = 4.7). These biorecognition events were assessed from the changes in the ionic current flowing through the nanochannel.
A new, simple, and short route for the synthesis of simplactones A ( 1 ) and B ( 2 ) was achieved from a synthetically prepared chiral auxiliary, i.e., the Oppolzer camphor‐derived sultam 4 , and (4‐methoxybenzyl)‐protected 3‐hydroxypropanal, in 52 and 48% overall yield, respectively, and with high diastereoselectivity (Schemes 2 and 3). 相似文献
The efficient chiral Ru3(CO)12 systems were prepared in situ from Ru3(CO)12 and various chiral diiminoor diamino-diphosphine tetradentate ligands. The systems have been used for the asymmetric transfer hydrogenation of propiophenone in 2-propanol, leading to 1-phenyl-1-propanol in a 98% yield and 96% e.e. The IR study suggests that the carbonyl hydride anion [HRu3(CO)11]^- most probably exists as a principal species under the reaction conditions. The high chiral efficiency may be due to the synergetic effect produced by the neighboring ruthenium atoms and a special chiral micro-environment involving the polydentate ligand and the Ru3 framework. 相似文献
Human immunodeficiency virus (HIV) infection is the fifth most common cause of death and many new HIV infections occur every year. The prevalence of HIV also seriously affects the quality of a patient’s life. More than forty anti-HIV drugs have been put into clinical uses, many of which are chiral molecules with multiple stereogenic centers, for example abacavir, lamivudine, zidovudine, stavudine, tenofovir, atazanavir. However, the chemical synthesis of these chiral intermediates have the disadvantages of low enantiomeric purity and complex synthetic steps. The benefits of asymmetric biosynthesis of chiral drugs include high enantiomeric excess (e.e.), good product selectivity, mild reaction conditions, and less side effects. The biosynthesis of the chiral intermediates of these anti-HIV drugs is thus particularly important. Herein, we review the different sources of enzymes and microbial cells for the asymmetric biosynthesis of the above chiral anti-HIV drug intermediates. We also review recent biotechnology progress in engineering these enzymes and microbial cells with improved biocatalytic activities, including enzyme and cell immobilization, surface display of enzymes, and directed evolution of enzymes. These biotechnology processes enable the efficient biosynthesis of these chiral intermediates, facilitating the industrial production of anti-HIV drugs with reduced costs. 相似文献