Organosulfur phosphonium salt-mediated synthesis of functionalized thiopyran derivatives

Methyl 4-oxotetrahydro-2H-thiopyran-3-carboxylate as a CH-acid undergoes a mild reaction with acetylenic esters in the presence of triphenylphosphine to produce phosphorus ylides possessing thiopyran-4-one ring moiety. The resulted phosphorus ylides when heated in toluene afforded functionalized thiopyran derivatives through intramolecular Wittig reaction.     

The Important Role of the Byproduct Triphenylphosphine Oxide in the Magnesium(II)‐Catalyzed Enantioselective Reaction of Hemiacetals and Phosphorus Ylides

By employing a simple in situ generated magnesium catalyst, a direct asymmetric reaction between hemiacetals and phosphorus ylides was achieved through a tandem Wittig–oxa‐Michael reaction sequence. Enantioenriched chromans, isochromans, and tetrahydropyrans were obtained in good chemical yields, and (?)‐erythrococcamide B was synthesized in enantioenriched form. The byproduct triphenylphosphine oxide was identified as a necessary additive for this process.     

手性钛锆化合物在不对称合成中的应用

本文综述了近年来手性钛锆化合物在不对称合成中的应用, 特别是手性柄型金属钛和锆化合物在不对称合成中的应用。对这类催化剂的特点和前景作了简要介绍。     

手性炔丙醇的不对称催化合成研究进展

手性炔丙醇是一种重要中间体化合物,作为合成多种光学活性化合物的重要合成前体受到学者们广泛关注。目前通过酮的不对称催化反应合成手性炔丙醇的研究开发具有极大发展前景,因此本文围绕酮类化合物的不对称催化反应来进行综述,结合相关反应最新研究进展,全面总结并分类了不对称催化还原、催化不对称加成等反应类型,介绍了合成不同结构手性炔丙醇的新思路,并对酮的不对称催化反应在未来能成为工业化重要生产途径作出展望。     

Efficient synthesis of functionalized olefins by Wittig reaction using Amberlite resin as a mild base

A convenient procedure for the synthesis of olefins by the reaction of stabilized, semistabilized, and nonstabilized phosphorous ylides with various aldehydes or ketone using Amberlite resin as a mild base is described. Our developed method offers facile and racemization-free synthesis of α,β-unsaturated amino esters and chiral allylic amine. The developed methodology offers mild reaction conditions, high efficiency, and facile isolation of the final products, a practical alternative to known procedures.     

Hexacoordinated phosphates: how to teach old chiral anions new asymmetric tricks

Chemical reactions and processes often involve chiral, yet racemic, cationic reagents, intermediates, or products. To afford instead nonracemic or enantiopure compounds, an asymmetric ion pairing of the cations with enantiopure anions can be considered--the counter ions behaving as asymmetric auxiliaries, ligands, or reagents. Detailed herein is a short review of our approach toward gaining reliable and predictable control over stereoselective ion pairing phenomena through the synthesis and use of novel configurationally stable hexacoordinated phosphate anions.     

Highly diastereoselective nitroaldol reactions with chiral derivatives of glyoxylic acid

N-Glyoxyloyl-(2R)-bornane-10,2-sultam (1a) and (1R)-8-phenylmenthyl glyoxylate (1b) react stereoselectively with simple nitroalkanes giving diastereomeric nitroalcohols with high asymmetric induction. The glyoximide 1a is proved to be a highly efficient chiral inducer, superior to glyoxylate 1b. In all cases, the absolute configuration (2S) and relative configuration, syn for the major diastereoisomers, were confirmed.     

Absolute asymmetric synthesis of "chiral-at-metal" Grignard reagents and transfer of the chirality to carbon

Two new six-coordinate Grignard reagents, cis-[(p-CH(3)C(6)H(4))MgBr(dme)(2)] (1) and cis-[MgCH(3)(thf)(dme)(2)]I (2), have been synthesized and their crystal structures have been determined. Both reagents are cis-octahedral and therefore chiral. They crystallize as conglomerates and racemize rapidly in solution. By utilizing these properties, the absolute asymmetric synthesis of specifically the Delta or the Lambda enantiomer was achieved for both Grignard reagents. Enantiopure 1 and 2 were then reacted with butyraldehyde or benzaldehyde to give the corresponding alcohol in up to 22 % enantiomeric excess. At -60 degrees C, the Grignard reagents crystallize as racemic phases instead of conglomerates. Consequently, the crystal structures of rac-cis-[(p-CH(3)C(6)H(4))MgBr(dme)(2)].DME (3) and rac-cis-[MgCH(3)(thf)(dme)(2)]I (4) could be determined.     

Facile and efficient synthesis of chiral sulfoxide esters: Versatile tool in asymmetric synthesis

Facile and efficient synthesis of sulfoxide esters using menthols as chiral auxiliary is described. Phenylthio/benzylthio/naphthylthioacetic esters act as an efficient substrate for chiral sulfoxides via oxidation in one step. The structural and stereochemical aspects of target product were established on the basis of various spectroscopic studies, namely FT-IR, NMR (¹H NMR and ¹³C NMR) and elemental analysis. This method is simple, fast, convenient and very efficient.     

Development of an amine dehydrogenase for synthesis of chiral amines

A leucine dehydrogenase has been successfully altered through several rounds of protein engineering to an enantioselective amine dehydrogenase. Instead of the wild-type α-keto acid, the new amine dehydrogenase now accepts the analogous ketone, methyl isobutyl ketone (MIBK), which corresponds to exchange of the carboxy group by a methyl group to produce chiral (R)-1,3-dimethylbutylamine.     

Synthesis and structures of new conformationally rigid 1-aza-1,3-dienes of the acenaphthene series

The Wittig reaction of 1-tert-butyliminoacenaphthen-2-one with benzylidenetriphenylphosphoranes produces new 1-aza-1,3-dienes of the acenaphthene series, which can bind butyllithium to the C=C bond of the enimine fragment C=C-C=N. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2206–2211, November, 2007.     

C2-symmetric chiral disulfoxide ligands in rhodium-catalyzed 1,4-addition: from ligand synthesis to the enantioselection pathway

A family of chiral C(2)-symmetric disulfoxide ligands possessing biaryl atropisomeric backbones has been synthesized by using the Andersen methodology. Complete characterization includes X-ray crystallographic studies of all ligands and some of their rhodium complexes. Their synthesis, optical purity, electronic properties, and catalytic behavior in the prototypical rhodium-catalyzed 1,4-addition of phenylboronic acid to 2-cyclohexen-1-one are presented through an in depth study of this ligand class. Density functional theory calculations on the step of the catalytic cycle that determines the enantioselectivity are presented and reinforce the first hypothetical explanations for the high levels of asymmetric induction observed.     

聚硅氧烷接枝酯类手性固定相的制备与表征

以S-(-)-乳酸甲酯、S-(-)-α-苯乙醇、(S)-(+)-仲丁醇为手性源,N,N'-二环己基碳二亚胺(DCC)为缩水剂、4-二甲氨基吡啶为酰化催化剂,分别与上述三种不饱和酸进行酯化反应设计合成出新的手性不饱和酯类单体,提纯产物,用红外扫描、核磁共振及有机元素分析表征确定了得到了纯净的产物。然后,以聚硅氧烷接枝手性单体,制备手性固定相。     

原位生成的烯丙基磷叶立德与醛的化学反应性研究

介绍了我们小组最近有关原位生成的烯丙基磷叶立德与醛的化学反应性研究结果.在化学计量叔膦作用下,烯丙基碳酸酯或联烯酸酯经原位生成的烯丙基磷叶立德活性中间体,与醛发生高度立体选择性的三组分Wittig烯化反应和vinylogous Wittig烯化反应,该类反应为合成多取代1,3-二烯衍生物提供了简单、高效的新方法;在催化量叔膦作用下,γ-甲基联烯酸酯经烯丙基磷叶立德关键中间体与醛发生多个膦催化的环化反应,为五元、六元含氧杂环化合物的合成提供了原子经济性的方法.通过氘代实验和核磁跟踪等方法,对上述反应机理进行了初步探索.     

Enantioselective conjugate addition of dialkylzinc and diphenylzinc to enones catalyzed by a chiral copper(I) binaphthylthiophosphoramide or binaphthylselenophosphoramide ligand system

The enantioselective conjugate addition of dialkylzinc or diphenylzinc to enones was catalyzed by a copper(I)-axially chiral binaphthylthiophosphoramide or binaphthylselenophosphoramide ligand system at room temperature (20 degrees C) or 0 degrees C, affording the Michael adducts in high yields with excellent ee for cyclic and acyclic enones. The enantioselectivity and reaction rate achieved here are one of the best results yet for the Cu-catalyzed conjugate addition to enones. It was revealed that this series of chiral phosphoramides was a novel type of S,N-bidentate ligands on the basis of (31)P NMR and (13)C NMR spectroscopic investigations. The mechanism of this asymmetric conjugate addition system has been investigated as well. We found that the acidic proton of phosphoramide in these chiral ligands play a significant role in the formation of the active species. A bimetallic catalytic process has been proposed on the basis of previous literature. The linear effect of product ee and ligand ee further revealed that the active species is a monomeric Cu(I) complex bearing a single ligand [Cu(I):ligand 1:1].