1,4-二氢吡啶衍生物的手性拆分及不对称合成进展

1,4-二氢吡啶衍生物(1,4-DHPs)具有广泛的生物活性,是重要的钙离子拮抗剂,详细介绍了拆分法以及不对称合成法制备光活性1,4-二氢吡啶衍生物的研究进展。拆分有化学拆分和酶拆分两种,化学拆分法主要包括经典成盐法和形成非对映体酯法,用于拆分1,4-DHPs的酶有脂肪酶和蛋白酶两种。分析了几种方法的优缺点,提出了今后的发展方向。     

对甲基苯磺酸催化一锅法合成1,4-二氢吡啶衍生物

以对甲基苯磺酸为催化剂,醛、乙酰乙酸乙酯(甲酯)和乙酸铵为原料,一锅法合成了系列标题化合物,产率75.9%～93.5%.其结构经1HNMR、FT-IR和EI-MS分析表征.     

Electrochemical oxidation of 2-methylnaphthalene-1,4-diacetate

Cyclic-voltammetric measurements show that 2-methylnaphthalene-1,4-diacetate is electrochemically oxidized on glassy-carbon electrode in glacial acetic acid at +1.45V vs SCE. The process is irreversible and diffusion controlled. Preparative controlled-potential electrolysis indicates that 2-methyl-1,4-naphthoquinone is a sole product. The material and current yields of the process are 94 and 99%, respectively.     

Synthesis of 1,4-dihydropyridine derivatives using nanocrystalline copper(II) oxide catalyst

Nanocrystalline copper(II) oxide catalyzed three-component coupling of aromatic amines, β-ketoesters and cinnamaldehyde to afford the corresponding 1,4-dihydropyridines in moderate to good yields under mild conditions is described. The catalyst can be recovered and reused for four cycles with almost consistent activity.     

Lewis acidic mesoporous Fe-TUD-1 as catalysts for synthesis of Hantzsch 1,4-dihydropyridine derivatives

Lewis acidic mesoporous material (TUD-1) containing Fe was investigated as stable and reusable catalyst for the synthesis of Hantzsch 1,4-dihydropyridine (DHP) derivatives. Yields between 76 and 91 % of DHP derivatives were obtained in shorter reaction times of 3 h depending on the nature of substituents in benzaldehyde.     

乙腈-水相1,4-二氯苯在铂电极上的电氧化行为

为有效去除化工废水中的1,4-二氯苯,研究了Pt电极上乙腈-水混合溶剂中1,4-二氯苯电氧化机理。计时电流法研究表明,氧化过程中既有电极表面失电子的直接电化学氧化,又有基于活性自由基的间接氧化。通过SEM表征和Pt电极表面观察,证明Pt电极在2.3 V(vs. SCE)的电位下氧化p-DCB过程中,表面存在黄色有机聚合物膜,致使体系的导电性变差。降解途径推断表明,反应首先经历了脱氯和对氯酚、对苯醌等芳香类中间体的生成;接着开环生成小分子有机酸;最后小分子羧酸进一步氧化成CO₂。     

Electrochemical oxidation of cholesterol in acetonitrile leads to the formation of cholesta-4,6-dien-3-one

Cholesterol was shown to be oxidized at the glassy carbon electrode in an acetonitrile–2-propanol mixture and this oxidation reaction was applied to the determination of serum total cholesterol by high-performance liquid chromatography with electrochemical detection (K. Hojo, H. Hakamata, A. Ito, A. Kotani, C. Furukawa, Y.Y. Hosokawa, F. Kusu, J. Chromatogr. A 1166 (2007) 135–141). To gain insight into the detection mechanisms of cholesterol, an electrolytic product of cholesterol was collected and characterized by infrared spectroscopy, one- and two-dimensional nuclear magnetic resonance, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The three techniques, together with comparisons of literature spectral data, confirmed the formation of cholesta-4,6-dien-3-one. The conversion of cholesterol to cholesta-4,6-dien-3-one, a four-electron, four-proton electrochemical process, has been proposed as an electrochemical oxidation mechanism of cholesterol in acetonitrile.     

Anodic oxidation of diphenyldiselenide in acetonitrile

The electrochemical behaviour of diphenyldiselenide in acetonitrile solution was studied by several electrochemical techniques. Controlled potential electrolysis in the presence of cyclohexene was also studied. The cyclic sweep voltammogram exhibited two irreversible anodic peaks at 1.35 and 1.65 V and one cathodic peak at ?1.25 V. It was concluded that the primary step is one-electron removal from the substrate, and the SeSe bond cleavage follows to generate phenylselenium cation and phenylselenium radical, of which the former species can react with cyclohexene to give mainly 2-acetamido-1-phenylseleno-cyclohexane. The possibility of utilizing phenylselenenic acid as the current mediator in the allylic hydroxylation reaction seems very limited. The cathodic reaction of diphenyldiselenide was also discussed briefly.     

The anodic oxidation of allyl alcohol in acetonitrile

The kinetics of the anodic oxidation of allyl alcohol in acetonitrile has been studied. At a platinum electrode at low potentials, < 2·6 V, the reaction is charge transfer controlled and at higher potentials the process becomes diffusion controlled. The reaction is not a simple charge-transfer process, but may proceed via an adsorption step. Controlled potential electrolysis yielded acrolein and polymers as products. The oxidation of allyl alcohol on platinum is probably electrocatalysed by “surface oxides”.     

Electrochemical behaviour of iron electrode in acidic acetonitrile solutions

Iron dissolution as well as hydrogen evolution was studied in HCl and HBr acetonitrile solutions in a concentration range between 2·8 × 10^?4 M. Halide concentration was changed by adding lithium halide to some of the previous solution. Measurements were performed at 0·0°C.Current efficiency for a two-electron transfer was about 100 per cent for both anodic and cathodic reactions.Corrosion and kinetic parameters were obtained from the polarization curves performed under different experimental conditions. Tafel slopes of 2·3 × 2 RT/F were found for both anodic and cathodic reactions.A reaction mechanism for the anodic reaction is postulated on the basis of anion adsorption. An inhibitory effect, probably due to solvent adsorption at the electrode, occurs as the acid concentration decreases, affecting both the anodic and cathodic polarization curves.     

Electrochemical degradation of polyfuran in wet acetonitrile and aqueous solutions

The degradation of polyfuran in a wet acetonitrile solution and in an aqueous solution has been investigated with a cyclic voltammetry technique, along with Fourier transform infrared and Fourier transform Raman spectroscopy techniques. Infrared spectroscopy shows that the main defects that exist in polyfuran after cycling in dried acetonitrile are mainly saturated C? H structures, whereas those after cycling in an aqueous solution are mainly carbonyl groups in the polymer chain. This may be because polyfuran can undergo degradation through a crosslinking mechanism in a dried acetonitrile solution, whereas in an aqueous solution, it undergoes degradation through a nucleophilic attack mechanism. Raman spectroscopy shows that not all the furan rings are involved in the degradation process, although the electrochemical activity of polyfuran is totally lost in an aqueous solution after only one cycle. The sites that are sensitive to the degradation process may be the electrochemically active sites, that is, the positively charged sites in polyfuran chains. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3160–3165, 2002     

Anodic oxidation of 2,6-xylenol in acetonitrile on platinum

Anodic oxidation of 2,6-xylenol at the platinum electrode in acetonitrile was investigated by the various electrochemical and chemical methods. Conductivity measurements indicated that the phenolic hydroxyl of 2,6-xylenol is undissociated in acetonitrile solution containing lithium perchlorate. By cyclic voltammetry and chronopotentiometry, it was shown that anodic oxidation of 2,6-xylenol at the platinum electrode proceeds in two steps. 2 electrons are involved in the first step, as determined by cyclic voltammetry using hydroquinone and DPPH as a reference compound. Polarographic study suggested that the first step is an electrophilic attack on the aromatic nucleus of the non-ionized phenol. The electrolysis products were analysed by thin-layer chromatography, ir and uv spectrophotometry and mass spectrometry. It is estimated that dimer, trimer and tetramer are produced by the anodic oxidation of 2,6-xylenol and that the dimer is 2,2′-dihydroxyl-3,3′-dimethylstilbene. The formation reactions of trimer and tetramer probably proceed by the same mechanism as dimer formation.     

Electrochemical oxidation of 1,4‐dioxane at boron‐doped diamond electrode

BACKGROUND: The electrochemical oxidation of 1,4‐dioxane at a boron doped diamond (BDD) surface on a niobium substrate anode was studied because (i) 1,4 dioxane is a resistant contaminant in waste‐waters and ground‐waters which needs to be removed/oxidized and (ii) most of the currently applied techniques for removal/oxidation require chemicals. RESULTS: Results show that in the potential region supporting electrolyte stability 1,4‐dioxane can be oxidized directly. Adhesive products, which cause electrode fouling, are also formed during oxidation in this potential region. The BDD anode can be restored to its initial activity by simple anodic treatment in the potential region of electrolyte decomposition. In this region, oxidation reactions leading to complete oxidation of 1,4‐dioxane, can take place due to electro‐generated hydroxyl radicals. Therefore, dioxane can only be effectively oxidized at these potentials. The effect of current density on the oxidation of 1,4‐dioxane has been investigated. The experimental results have also been compared with a theoretical chemical oxygen demand (COD)–instantaneous current efficiency (ICE) model. At a current density above 32 mA cm^?2, the oxidation process is completely controlled by mass transfer and no intermediates are formed. 92% of the COD can be removed with a total consumption of 7 Ah L^?1. CONCLUSIONS: Results show that dioxane can be effectively and completely oxidized at a BDD anode. Copyright © 2010 Society of Chemical Industry     

Crown ether complex cation ionic liquids: synthesis and catalytic applications for the synthesis of tetrahydro-4H-chromene and 1,4-dihydropyridine derivatives

A series of crown ether complex cation ionic liquids (CECILs) are synthesized by crown ethers chelated with sodium benzenesulfonates, and used as a green and environmental catalyst, for the synthesis of tetrahydro-4H-chromene and 1,4-dihydropyridine derivatives by three-component reactions of aromatic aldehydes and malononitrile with cyclic β-dicarbonyls or cyclic β-enaminoketones respectively, in H₂O/EtOH (1:1), at the reflux condition. CECILs, as a green and environmental catalyst, can be easily obtained and are stable. Furthermore, high conversions, short reaction times, and cleaner reaction profiles are some of the advantages of this method.     

Anodic oxidation of some polycyclic bridgehead iodides in anhydrous acetonitrile

The anodic oxidation of some polycyclic bridgehead iodides is reported in 0.5 M solutions of lithium perchlorate in anyhydrous acetonitrile, using rotating glassy-carbon disk electrodes. The ease of abstraction of an electron from the compounds is correlated with the steric strain at the bridgehead positions of the molecules. It is found that anodic acetamidation proceeds efficiently only for compounds of low steric strain.     

A facile,efficacious and reusable Sm2O3/ZrO2 catalyst for the novel synthesis of functionalized 1,4-dihydropyridine derivatives

An efficient four component/one-pot protocol was developed for synthesis of novel functionalized 1,4-dihydropyridines at room temperature by a reaction of malononitrile, substituted aldehydes, dimethylacetylenedicarboxylate and 4-fluoroaniline in ethanol and using Sm₂O₃/ZrO₂ as catalyst. All reactions were completed in < 20 min. The structures of all the new compounds were confirmed by different spectral analyses. The catalyst, Sm₂O₃/ZrO₂ was synthesized and characterized by various techniques including powder X-ray diffraction, N₂ adsorption/desorption, scanning electron microscopy, and transmission electron microscopy analysis. The key advantages of this process are good to high yields (87 to 96%), short reaction times, easy work-up, reusability and no chromatographic purification.     

Electrochemical synthesis of sulfonated polypyrrole in FSO3H/acetonitrile solution

The incorporation of SO₃^? groups into a polypyrrole backbone was successfully carried out using FSO₃H/acetonitrile medium. The degree of sulfonation (sulfonation or sulfur‐to‐nitrogen ratio) of polymer was controlled by varying FSO₃H concentration while the film was being electrodeposited. The cyclic voltammograms of the electrodeposited films were taken between ?1.00 and +2.00 V (versus Ag/AgCl) in blank solution. A substantial effect on the electrical conductivity was observed upon the incorporation of SO₃^? groups in the polypyrrole polymeric chain. The elemental analysis results of the freshly prepared and reduced films give independent evidence that the SO₃^? groups are covalently bound to the structure. FTIR, UV‐Vis, spectroscopy and SEM techniques were used to characterize the electrosynthesized polypyrrole films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 526–533, 2004     

Electrochemical study of 7α,12,20-O-trimethyl-conacytone in acetonitrile

An electrochemical study of the electroreduction in anhydrous acetonitrile of 7α,12,20-O-trimethyl-conacytone, an abietane quinoid diterpene derivative from the natural product 7α-O-methyl-conacytone, showed two reduction signals. At the first reduction step, fast chemical reactions involving the loss of the methoxyl group located at C-7 with simultaneous regeneration of the quinoid moiety were observed. This electrogenerated quinone is reduced again, at the same potential used with the former quinone, resulting in a two-electron peak. These results were obtained by cyclic voltammetry and double-step chronoamperometry experiments. The electrolysis under methylating conditions of 7α-O-methyl-conacytone, at potential values of the second electron transfer, generates as major products, methoxy-hydroquinone, where the methoxy group at C-7 is lost, which is in agreement with the proposed mechanism. Therefore, the second reduction signal was attributed to the reduction of semiquinone intermediates by a mechanism not elucidated.