Epimerization, diastereoselectivity and hemilability in dicationic chiral ruthenium complexes with bidentate (PS) bisphosphine monosulfide ligands

The binding of heterobidentate P^∧S ligands introduces metal-centered chirality to the planar chiral parent complex Ru(η⁶:η¹-NMe₂C₆H₄C₆H₄PCy₂)Cl₂. Observed diastereomeric ratios for the kinetic product vary dramatically depending upon ring size of the chelate formed with the P^∧S ligand. The complexes epimerize very slowly to thermodynamic product ratios that are substantially different from the kinetic product ratios.     

固体CD光谱研究及其应用于手性席夫碱M(II)配合物

结合课题组近期的相关研究,对固体CD光谱在手性配合物研究中的应用,特别是手性样品固体CD光谱的测试方法进行了概述,通过对四对手性席夫碱M(II)(M=Ni、Cu)配合物的固体和溶液CD光谱进行比较研究,发现配合物的手性构型在固液相中保持一致,但其固液CD光谱之间存在不同程度的差异,可能是由于相应配合物在固体和溶液相中的四面体扭曲或构象的微妙不同所致.     

Electrochiroptical systems based on biphenyl-2,2′-diyl-type dicationic dyes: strong chiroptical signals through the transmission of point chirality to axial chirality

Huge CD amplitude (A = +538) was attained by diastereomeric preference (50% de) for the title dication with two bis[4-(R)-sec-butoxyphenyl]methylium units in benzene at 23 °C. Intramolecular π-π stacking is the origin for effective transmission of point chirality to axial chirality to attain the chiroptical enhancement of 400-times. Thanks to the strong CD signaling, chiroptical changes upon electrolysis could be readily detected, thus realizing a new class of electrochiroptical response systems. Chiroptical properties could also be modified by solvent polarity.     

Chiral Derivatives of Achiral Molecules: Standard Classes and the Problem of a Right-Left Classification

Chemistry judging by its applications, physics according to its methods, and heavily reliant upon the tools of mathematics—that is what makes theoretical chemistry. And yet that is where its strength lies—in the variety of these sciences. It is quite natural that, in answer to specific problems, results and methods can sometimes be developed whose scope extends far beyond the original application. Rather it is a mark of quality if consequences can be found in chemistry and physics and the pathway leads via new mathematical procedures and concepts. Regrettably, any publication aiming to present such aspects will usually encounter little resonance since the linguistic confusion in science, its disciplines, and subdisciplines, lies like a veil over our understanding. The author nevertheless wishes to attempt to present, in a series of articles, results of research into chemical themes in a manner designed to appeal to the interest of chemists, without neglecting interdisciplinary aspects. All that is required to understand the argumentation is a lively interest. The first two articles are concerned with the chirality of molecules, and in particular with questions relating to the chirality phenomenon of molecules in the framework of molecular classes. In view of the algebraic nature of the mathematical methods adopted, it is not surprising that precise statements result. It appears of primary interest to establish the degree to which such statements can be considered valid for molecular models or molecules themselves.     

A stereoselective synthesis of asymmetrically substituted calix[4]arenecarbamates

Calix[4]arenes bearing a methoxy and an R or S α-phenylethylacetamido group at the narrow rim of macrocycles are stereoselectively acylated with 1 equiv of trichloroacetyl isocyanate to give chiral asymmetrically substituted calix[4]arenecarbamates in preparative yields and high diastereomeric excess.     

trans-Bis-[(−)ephedrinate]-palladium complex: synthesis, molecular modeling and use as catalyst

The reaction between palladium acetate, (−)-ephedrine and potassium acetate led to bis-chelate complex Pd[OCH(Ph)NH(Me)]₂ whose the trans-structure is obtained from calculations. The use of this complex to catalyze either the 1,4-hydrogenation of (E)-2-benzyliden-1-tetralone or Heck reaction of phenyl iodide with 3-methyl-3-buten-2-ol led to a low enantiomeric excess.     

(2S,3S,4R)-2-正戊基-3,4-二叠氮基四氢噻吩的合成

以（＋）－4，10－二氧杂三环[5.2.1.O^2,6]－癸－8－烯－3－醇为原料。经8步反应，对映选择性地合成出去氧维生素H的重要中间体：（2S，3S，4R）－2－正戊基－3，4－二叠氮基四氢噻吩。为对映选择性合成手性四氢噻吩类化合物提供了新的方法。     

胆汁酸盐-胆红素-钙离子三元复合物的构象性质

根据九种胆汁酸盐-胆红素-钙离子三元体系的UV和CD实验所见, 提出一种所形成的三元复合物的构象模型。利用PPP-SCF-CI-DV量子化学程序拟合有关的UV和CD谱, 研究三元复合物的构象性质。得到两类六种与光谱学实验符合的胆红素分子的最佳构象。利用它们可以解释九种胆汁酸盐-胆红素-钙离子三元复合物表现在园二色谱中的手性性质。     

Partial transfer of enantioselective chiralities from α-methylated amino acids, known to be of meteoritic origin, into normal amino acids

There is overwhelming evidence that meteorites bring α-methylated amino acids to earth with some l(S) enantiomeric excess. How does that get transferred into normal biological molecules? In this brief account, we show that an α-methylated amino acid, d(R)-α-methylvaline, can react with pyruvate and phenylpyruvate salts in dry mixtures to form alanine and phenylalanine with l enantiomeric excesses, under sensible prebiotic conditions. Thus the meteoritic l(S) excesses of this compound would produce excess d-alanine and d-phenylalanine, which are found in some organisms.     

Catalyst-substrate helical character matching determines enantiomeric excess

In the framework of a helix theory recently developed for molecular chiralities and chiral interactions, it is further proposed that for an asymmetric reaction to be highly enantioselective, the helical characters, that is, the local energies of electrons on the helices, of the catalyst and the substrate complexed with it in the corresponding enantioselection-determining step must be matched. These helical characters can be analyzed on the basis of molecular polarizability and structure properties under a given reaction mechanism. This proposal highlights the importance of polarizability matching in three-dimension chiral space and in essence is a chiral version of the classical hard and soft acid-base theory. It also from an electronic effect angle sheds light on the nature of the conventional lock-and-key origin of high enantioselection and carries the message that, to design a good catalyst (the key), rather than focusing on the rigidity, bulkiness or C₂-symmetry of the catalyst, one should focus more on the helical character of the substrate (the lock) with which the catalyst will interact. It is generally easier to discover a highly enantioselective catalyst for a substrate of a large helical character than for a substrate of a small helical character. The proposal is supported by theoretical modeling as well as numerous experiments and is used to understanding various aspects of current asymmetric catalysis.