Molecular self-modification: homolog of a manganese laundry bleach catalyst oxidatively transforms its tetradentate ligand into a novel hexadentate derivative

On the basis of mass spectral studies alone, the relatively new manganese complex, Mn(Et₂EBC)Cl₂ (Et₂EBC = 4,11-diethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane), a homolog of the well proven, peroxide-based laundry bleach, Mn(Me₂EBC)Cl₂, has been reported to undergo a sequence of 2-electron oxidation steps, ultimately converting its ethyl groups into chelated ethoxo and methylene carboxylato groups, [Mn^IV{(^?OCH₂CH₂)(^?O₂CCH₂)}EBC)](PF₆)₂. We report here the isolation and characterization of that unusual product, and provide insight into the remarkable catalytic pathway to its formation. At temperatures above 0 °C, oxidation by aqueous H₂O₂ reliably transforms Mn(Et₂EBC)Cl₂ into [Mn^IV{(^?OCH₂CH₂)(^?O₂CCH₂)}EBC)]²⁺. The experimental data for this intramolecular ethyl group transformation is consistent with oxygen insertion into a methyl C?CH moiety of the ethyl group, ?CNCH₂C(?CH)H₂, by the Mn^IV?COOH functional group.     

Synthesis, crystal structure and optical properties of the new lead fluoride borate—Pb2BO3F

A new compound, Pb₂BO₃F, has been grown by high temperature solution method from the PbO–PbF₂–B₂O₃ system for the first time. The crystal structure of this compound has been identified by single crystal X-ray diffraction analysis. It crystallizes in the hexagonal system, space group P6₃/m (No. 176) with unit-cell parameters a=7.2460(3) Å, c=14.5521(17) Å, Z=6, V=661.69(9) ų. Its structure was solved by the direct methods and refined to R₁=0.0163 and wR₂=0.0367. The structure of Pb₂BO₃F consists of the distorted PbO₃F₂ groups and BO₃ triangles, which are all symmetric with each other in the gestalt structure to the extent that the Pb₂BO₃F compound crystallizes in the symmetric space group. The powder X-ray diffraction pattern of the Pb₂BO₃F has been measured. The BO₃ functional groups presented in the sample were identified by FTIR spectrum. The DTA curve of Pb₂BO₃F suggests that Pb₂BO₃F melts congruently at 448 °C.     

Voltammetric sensing of paracetamol, dopamine and 4-aminophenol at a glassy carbon electrode coated with gold nanoparticles and an organophillic layered double hydroxide

A differential pulse voltammetric method was developed for the simultaneous determination of paracetamol, 4-aminophenol and dopamine at pH 7.0 using a glassy carbon electrode (GCE) coated with gold nanoparticles (AuNPs) and a layered double hydroxide sodium modified with dodecyl sulfate (SDS-LDH). The modified electrode displays excellent redox activity towards paracetamol, and the redox current is increased (and the corresponding over-potential decreased) compared to those of the bare GCE, the AuNPs-modified GCE, and the SDS-LDH-modified GCE. The modified electrode enables the determination of paracetamol in the concentration range from 0.5 to 400???M, with a detection limit of 0.13???M (at an S/N of 3). The sensor was successfully applied to the stimultaneous determination of paracetamol and dopamine, and of paracetamol and 4-aminophenol, respectively, in pharmaceutical tablets and in spiked human serum samples.

Solvothermal syntheses and crystal structures of two new thiogermanates [M(dap)3]4Ge4S10Cl4 (M?=?Co, Ni) with metal complexes as counterions

Abstract  

Two new transition-metal thiogermanates [M(dap)₃]₄Ge₄S₁₀Cl₄ (M = Co, Ni; dap = 1,2-propanediamine) have been solvothermally synthesized and structurally characterized. The two thiogermanates are isostructural and consist of discrete Ge₄S₁₀⁴⁻ adamantane-like ions, free Cl⁻ ions, and [M(dap)₃]²⁺ cations as counterions. The Ge₄S₁₀⁴⁻ anion is built from corner-sharing connection of four GeS₄⁴⁻ tetrahedra. Although some chalcogenidogermanates have been obtained by use of in situ generated transition-metal complexes as structure-directing agents under mild solvothermal conditions, their anions are usually dimeric [Ge₂Q₆]⁴⁻ (Q = S, Se) species. The new thiogermanates are rare examples of adamantane-like (Ge₄S₁₀⁴⁻) thiogermanates combined with transition-metal complexes. Their optical properties have been investigated by UV–Vis spectra.     

Bifunctional cinchona alkaloids-catalyzed asymmetric [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones

A highly enantioselective [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones was realized with readily available cinchona alkaloids as the catalysts. Using this reaction, a series of highly functionalized δ-lactones with adjacent α-quaternary-β-tertiary stereocenters were obtained in high yields (up to 97%) and with good-to-excellent enantioselectivities (up to 97% ee).     

Double asymmetric induction as a mechanistic probe: the doubly diastereoselective conjugate addition of enantiopure lithium amides to enantiopure α,β-unsaturated esters and enantiopure α,β-unsaturated hydroxamates

The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure α,β-unsaturated esters [derived from Corey’s 8-phenylmenthol chiral auxiliary] and enantiopure α,β-unsaturated hydroxamates [derived from our ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine] has been used as a mechanistic probe to determine the reactive conformations of these acceptors.     

具有叶绿素基本碳架的C-3-异噁唑啉基二氢卟吩类衍生物的合成

以脱镁叶绿酸-a甲酯为起始原料,通过3-位乙烯基与氧化苯甲腈和4-取代氧化苯甲腈的1,3-偶极环加成反应,分别得到3-位异噁唑基取代的二氢卟吩衍生物以及其他形式的加成产物,对其脱镁叶绿酸的E-环结构修饰则转换成相应的二氢卟吩-p6衍生物;脱镁叶绿酸-a甲酯经空气氧化和重排反应形成了红紫素-18-内酰胺,再与4-取代氧化苯甲腈进行相同的环加成反应,也以理想的产率生成标题化合物.所得新的二氢卟吩衍生物的化学结构均经UV,IR,1H NMR 及元素分析得以证实,并对相应的反应提出可能的反应机理.     

2-(4-β-D-吡喃阿洛糖苷-苯基)-5-取代芳基-1,3,4-噁二唑的合成及镇静活性研究

以豆腐果苷为原料, 与取代苯甲酰肼反应生成中间体4-β-D-吡喃阿洛糖苷-苯甲醛取代苯甲酰腙(2a～2g), 在溴作催化剂的条件下发生关环反应, 合成了一系列豆腐果苷类似物3a～3g. 所有化合物结构经IR, ¹H NMR以及MS谱得以证实. 初步药理实验结果表明, 化合物3a, 3c, 3f与豆腐果苷相比有更好的镇静活性.     

无溶剂合成1,3,5-三芳基-2-芳酰基环己醇衍生物和晶体结构

在NaOH存在下室温研磨查尔酮与丙二腈,可以有效地得到1,3,5-三芳基-2-芳酰基环己醇衍生物,本合成方法反应时间短、操作简单、产率高,符合绿色化学特点.产物结构经过红外、核磁、元素分析和高分辨质谱确证,并对3b做了单晶衍射测定.     

Asymmetric cycloaddition of β,γ-unsaturated α-ketoesters with electron-rich alkenes catalyzed by a chiral Er(OTf)3/N,N'-dioxide complex: highly enantioselective synthesis of 3,4-dihydro-2H-pyrans

The asymmetric inverse-electron-demand hetero-Diels-Alder (HDA) reactions of β,γ-unsaturated α-ketoesters with electron-rich alkenes were investigated, with an N,N'-dioxide/erbium(III) complex employed as the catalyst. Quantitative conversion of the β,γ-unsaturated α-ketoesters and excellent enantioselectivities (up to >99% ee) and diastereoselectivities (up to >99:1 d.r.) were observed for a broad range of substrates by using a 0.5-0.05 mol% catalyst loading under mild reaction conditions. The reaction could be scaled up to the gram scale with the same results. In addition, this was the first application of Er(OTf)(3) to the asymmetric inverse-electron-demand HDA reaction and it behaved as an efficient catalyst. Moreover, the synthetic utility of this methodology was demonstrated with the synthesis of key intermediates of some natural products.