Effect of aryl ligands on the chemical hardness of arylmercury cations

¹⁹F NMR spectroscopy was used to study the exchange reactions involving 4-fluorothiophenoxides, 4-nitrophenoxides, chlorides, and acetates of arylmercury and triphenylphosphinegold. The analysis of the data on equilibrium constants allows one to obtain information on the comparative chemical hardness of ArHg⁺ and Ph₃PAu⁺ cations. The increase in the electron-donating ability of aryl ligands enhances the chemical hardness of ArHg⁺ cations, their influence being best described by ⁰ constants of substituted phenyl groups.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1255–1260, May, 1996.     

Catalytic, asymmetric synthesis of α,α-disubstituted amino acids

Copper(salen) complex 1 has been found to catalyse the asymmetric alkylation of enolates derived from a variety of amino acids. There is a clear relationship between the size of the side chain in the substrate and the enantioselectivity of the process, so that the enantioselectivity decreases in the order alanine>aminobutyric acid>allylglycine>leucine>phenylalanine>valine. A transition state model which accounts for the influence of the size of the side chain on the enantioselectivity of the reactions is presented.     

N-(6-甲基-2-亚甲基吡啶)-( )-樟脑亚胺体系的不对称烷基化反应

目前,不对称合成光学活性化合物取得了较大进展,不对称合成α-氨基酸、β-氨基醇、α-取代苄胺的报道很多。但是,不对称合成生物碱类物质——α-取代氨甲基吡啶类化合物还未见文献报道,而此类化合物有潜在的应用前景。为此,我们以( )-樟脑为手性试剂     

Useful dual Diels-Alder behavior of 2-azetidinone-tethered aryl imines as azadienophiles or azadienes: a beta-lactam-based stereocontrolled access to optically pure highly functionalized indolizidine systems

Imines derived from 4-oxoazetidine-2-carbaldehydes have been found to be versatile Diels-Alder reagents in that they exhibit two reactivity patterns. 2-Azetidinone-tethered imines undergo diastereoselective reaction with Danishefsky's diene in the presence of different Lewis acids. The effect of the amount of catalyst on the conversion rate as well as on the product ratio has been studied. Under standard reaction conditions, indium(III) chloride and zinc(II) iodide provided the best yields, and indium(III) triflate the highest diastereoselectivity in the Lewis acid promoted aza-Diels-Alder cycloaddition. Treatment of the aforementioned imines with cyclopentadiene, 2,3-dimethyl-1,3-butadiene or 3,4-dihydro-2 H-pyran led to cycloadducts arising from inverse electron-demand condensation involving the beta-lactam-tethered aryl imine as the heterodiene component. In addition, the first methodology for preparing indolizidines from beta-lactams has been developed. This process involves amide bond cleavage of the beta-lactam ring in the aza-Diels-Alder cycloadducts with concomitant cyclization. Full chirality transfer occurs when the reaction is performed with an enantiomerically pure substrate.     

Asymmetric Diels–Alder reactions in supercritical carbon dioxide catalyzed by rare earth complexes

The rare earth(III) salt catalysed asymmetric Diels–Alder reaction of cyclopentadiene with a chiral dienophile in supercritical carbon dioxide (scCO₂) proceeded rapidly to give the adduct with a higher diastereoselectivity than that in dichloromethane; Yb(ClO₄)₃ gave the endo adduct with value up to 77% de at 40°C, 8 MPa. The chiral rare earth diketonate catalyzed hetero Diels–Alder reaction of the Danishefsky's diene with benzaldehyde gave a higher yield and an enantioselectivity in scCO₂ than that in dichloromethane. Scandium/pybox 8a complex catalysed asymmetric Diels–Alder reaction of 3-crotonoyl-2-oxazolidinone with cyclopentadiene in the presence of MS4A proceeded smoothly in scCO₂ to give the endo adduct 10 in a good yield with up to 88% ee.     

An aldol approach to the total synthesis of (+)-brefeldin A

A convergent selective route to (+)-brefeldin A (BFA) and 7-epi-BFA was developed, with the crucial C-4/C-5 stereogenic centers were established using Crimmins asymmetric aldolization.     

Surface structures of adsorption layers of sodium hyaluronate and bovine serum albumin complexes on poly(γ-methyl-l-glutamate) film and their surface properties

Two-dimensional structures and characteristics of the complexes between sodium hyaluronate (NaHA) and bovine serum albumin (BSA) were studied by using a quartz crystal microbalance method and an atomic force microscope (AFM). NaHA did not adsorb on poly(-methyl-l-glutamate) (PMLG) film. On the other hand, the complexes adsorbed on it and the adsorption behaviors were found to be Langmuir types. With increasing weight ratio of BSA to NaHA, W _BSA, the adsorption constants K decreased and the saturated adsorption masses increased. The adsorbed complexes were spherical particles and at saturated adsorption states they covered compactly on the PMLG film. The mean diameters d _AFM estimated from the topographic images decreased from 70 to 54 nm with increasing W _BSA. The adhesion force F _ad and the frictional force F _f between the complex layers and the AFM tip were obtained by using the contact mode of the AFM. With increasing W _BSA, the values of F _ad decreased and the values of F _f increased. Compared with the frictional coefficient of the NaHA adsorption layer on the BSA monolayer, the values for the NaHA–BSA complex layer were found to be much higher.     

金在酸性硫脲溶液中的阳极溶解过程

采用循环伏安法、旋转金盘电极和库仑电解等方法研究了金在酸性硫脲(TU)溶液中的阳极溶解过程。提出了金的阳极溶解机构。认为表面的Au(TU)_(ads)~ 的“化学溶解”步骤是过程的控制步骤。由此解释了旋转金盘电极的极化曲线出现电流峰以及金的溶解速度出现极大的原因。