关键词： imines   asymmetric synthesis   amino acids   Schiff bases   alpha,beta-didehydro-alpha-amino acids  

摘要： The present paper is an overview of new methods for the asymmetric synthesis of different types of alpha-amino acids. These methods are based on alkylation and condensation reactions of glycine and alanine imine derivatives, which can be carried out under very mild and simple reaction conditions. The enolates generated from these types of reagents are very soft and can be alkylated in a highly diastereoselective manner, even at room temperature, by using chiral templates or asymmetric PTC conditions. These methodologies afford monoalkylated and dialkylated alpha-amino acids as well as heterocyclic derivatives. In the case of cyclic imine derivatives with oxazinone or pyrazinone structures, the condensation reaction under PTC conditions or with Eschenmoser's salt allows the preparation of chiral alpha,beta-didehydro-alpha-amino acid derivatives which can be hydrogenated, cyclo-propanated or submitted to Diels-Alder cycloadditions to afford N-methylated and cyclic alpha-amino acids.

关键词： amino acids   asymmetric synthesis   pyrazinones   phase-transfer catalysis   palladium  

摘要： (6R)-6-Isopropyl-3-methyl-5-phenyl-1,2,3,6-tetrahydro-2-pyrazinone, obtained from (R)-valine and (S)-alanine, is highly diastereoselectively alkylated at room temperature by: a) activated alkyl halides under solid-liquid PTC conditions, b) non-activated alkyl halides with organic bases, c) electrophilic olefins employing both solid-liquid PTC conditions and organic bases, and d) allylic carbonates by means of palladium catalysis under neutral conditions. Enantiomerically pure (S)-alpha-methyl alpha-amino acids 8 are obtained by hydrolysis of the alkylated pyrazinones.

关键词： dehydroalanine   thiols   addition   diastereoselectivity   S-alkylcysteines   asymmetric synthesis  

摘要： An efficient procedure was developed for the asymmetric synthesis of S-alkyl derivatives of (R)-cysteine by nucleophilic addition of alkanethiols ((BuSH)-S-n, (BuSH)-S-t. or tert-C5H11SH) to the C=C bond of the dehydroalanine fragment in the Ni-11 complex of the Schiffs base of Delta-Ala with (S)-2-N-(N-benzylprolyl)aminobenzophenone [(S)-BPB-Delta-Ala]Ni-11. Under conditions of thermodynamic control of the reaction, the diastereomeric excess of the complexes with the (S, R)-configuration was 88-96%. After decomposition of the complexes, ( R)-S-butylcysteine, (R)-S-tert-butylcysteine. and (R)-S-tert-pentylcysteine were isolated with an enantiomeric purity of >97%.

关键词： 4-丁内酯/化学合成   4-丁内酯/化学   4-丁内酯/代谢   异山梨酯/化学   异山梨酯/代谢   酮类/代谢   甲基丙烯酸盐/代谢   质子   立体异构现象  

摘要： [GRAPHICS] Using an easily accessible and inexpensive chiral auxiliary derived from isosorbide, optically active alpha,gamma-substituted gamma-butyrolactones were obtained in high enantiomeric purity (up to >99% ee for trans) by the Sml(2)-induced reductive coupling of chiral methacrylate 7 with ketones in the presence of (-)-sultam as a proton source.

关键词： 均相催化不对称氢化   不对称合成   手性双膦配合物  

摘要： 手性双膦配体 2 ,2′-双 (二苯基膦基 ) - 1,1′-联萘与钌、铑离子形成的配合物可作为高效均相催化剂 ,用于烯烃和羰基的高对映选择性氢化 ,或烯烃的对映选择性异构化。本文对此领域的研究状况进行简介。

关键词： 有机锡化合物   天然产物   不对称合成   催化  

摘要： 综述了有机锡化合物在不对称合成天然产物中的应用。有机锡化合物应用于天然产物的不对称合成 ,反应条件温和、活性高、有很高的立体选择性和区域选择性 ,有广阔的应用前景。

关键词： beta-amino acids   asymmetric synthesis   peptidomimetics   ketenes   (R)-pantolactone   deracemization  

摘要： The synthesis of racemic N-phthalyl beta 2-homoarylglycines 5 and their asymmetric transformation have been investigated. The key step is the stereoselective addition of the (R)-pantolactone to the corresponding prochiral ketene 7.

关键词： asymmetric synthesis   lactams   antibiotics   ab initio calculations   cyclization reactions  

摘要： Reaction of N-trialkylsilylimines with a variety of glycine-derived ketenes produced 1,S-azadienes, which in some cases have been isolated and characterised. A conrotatory ring closure of these compounds gave rise to the formation of the azetidine-2-ones, thus allowing a formal two-step Staudinger reaction. Exclusive trans diastereoselectivity was observed. A less stringent diastereofacial selectivity was obtained. A set of experiments has been performed in order to evaluate the influence of the structural parameters as well as reaction renditions. Ab initio studies at MP2/6-31G* and QCISD(T)/ 6-311G** levels on model compounds provide a rationalization of the experimental results obtained. From the experimental as well as theoretical data it is clear that the presence of the silyl enol group in the intermediate azadiene is crucial in its stabilisation and plays a fundamental role in the conrotatory ring closure and, therefore, in the formation of the azetidine-2-one ring.

关键词： Chromium   Amides   Lithiation   Alkyls   Lithium  

摘要： Axially chiral N-methylanilides were synthesized by enantioselective lithiation of prochiral tricarbonyl(N-methyl-N-pivaloyl-2,6-dimethylaniline) chromium (1) with the lithium amide of the 4-methylpiperazinylethylamine derivative 13 followed by electrophilic quenching up to 97% ee in good yields. The resulting axially chiral chromium-complexed anilides 2 were oxidized under air to give the axially chiral anilides 14 in enantiomerically active form without axial bond rotation at room temperature.

关键词： Planar chirality   Ferrocene derivatives   Diphosphine ligands   Ortho-lithiation   Kinetic resolution   Phosphine-ligands   Bite angle   Complexes   Catalysis   Stereochemistry  

摘要： Two novel phosphorus-chiral ligands, 2,2'-bis(arylphenylphosphino)-1,1'-biferrocenyls 1a (aryl = 1-naphthyl) and 1b (aryl = 2-biphenylyl), have been prepared in enantiopure form by stereoselective multistep synthesis. While asymmetry on phosphorus was established via nucleophilic substitution reactions at borane-protected phosphorus centers, orthoiodination of the derived optically pure ferrocenylphosphine oxides served as the key step for the introduction of planar chirality. Utilizing biphenylylphenylphosphinoxyferrocene, 5b, the latter reaction was found to proceed in a highly diastereoselective manner, resulting in a product distribution of 97:3. The absolute configuration of the predominantly formed diastereomer was confirmed by crystal structure analysis of the Ullmann-coupled bis-(arylphenylphosphinoxy)biferrocenyl 6b (aryl = biphenylyl). Reduction of dioxides 6a (aryl 1-naphthyl) and 6b gave rise to the enantiopure C-2-symmetrical title compounds comprising four adjacent stereocenters. The coordination behavior of la was investigated by a crystal structure determination of its Pt(II) dichloride complex 8a and compared with the structure of complex 8c, bearing the related 1,1'-bis(1-naphthylphenylphosphino)ferrocene ligand 1c.