Electrochemical oxidation of 4-monoalkyl-substituted 1,4-dihydropyridines

The electrochemical oxidation of 4-monoalkyl-substituted 1,4-dihydropyridines has been studied in an aprotic medium and in the presence of pyridine. In an aprotic medium the products of oxidation are both 4-alkyl-substituted and 4-unsubstituted pyridines or mixtures of them. On oxidation in acetonitrile of 4-Et-, 4-n-Pr-, and 4-i-Bu-substituted dihydropyridines, 2-methylene-1,2,3,4-tetrahydropyridines were obtained in addition to the oxidized forms. In the presence of base the products of preparative electrolysis of the studied compounds were 4-alkyl-substituted pyridines. The exception was the 4-i-Pr- substituted dihydropyridine which was dealkylated on oxidation even in the presence of base. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1829–1838, December 2008.     

Special Features of the Electrochemical Oxidation of Substituted 4-Carboxy-1,4-dihydropyridines

Electrochemical oxidation potentials of 1,4-dihydropyridines substituted with 4-COOH, 4-COOR, and 4-CONRR' groups have been determined in aprotic acetonitrile by the rotating ring-disk electrode method (RRDE). The electrochemical reduction potentials of the resulting products were also determined at the ring electrode. It was established that protonated pyridines are formed in the oxidation of derivatives with and without a substituent in position 4 of the heterocycle. In the case of 4-alkoxycarbonyl substituted compounds the substituent at position 4 is generally retained. 1,4-Dihydrogenated derivatives of isonicotinic acid as a rule loose the substituent at position 4 on oxidation, and both types of product were recorded for the corresponding 4-carbamoyl derivatives. The substituent at position 9 of the heterocycle was mainly retained on electrochemical oxidation of the 3,3,6,6-tetramethyl-1,8-dioxo-1,2,3,4,5,6,7,8,9,10-decahydroacridine derivatives studi! ed.     

Electrochemical synthesis of 1,2,3,4,4,5,6-substituted 1,4-dihydropyridines

It has been shown that chemical oxidation of the methyl ester of 3,4,5-trimethoxycarbonyl-1,2,6-trimethyl-1,4-dihydropyridine to the pyridinium salt, requiring forcing experimental conditions, may be replaced by electrochemical oxidation. On electrochemical reduction of 3,4,5-trimethoxycarbonyl-1,2,6-trimethylpyridinium perchlorate in the presence of alkylating agents 1,2,3,4,4,5,6-substituted 1,4-dihydropyridines are obtained. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 226–237, February, 2007.     

Quantification of polyphenols with potential antioxidant properties in wines using reverse phase HPLC

A RP-HPLC method with photodiode array detection (DAD) was developed to separate, identify and quantify simultaneously the most representative phenolic compounds present in Madeira and Canary Islands wines. The optimized chromatographic method was carefully validated in terms of linearity, precision, accuracy and sensitivity. A high repeatability and a good stability of phenolics retention times (< 3%) were obtained, as well as relative peak area. Also high recoveries were achieved, over 80.3%. Polyphenols calibration curves showed a good linearity (r(2) >0.994) within test ranges. Detection limits ranged between 0.03 and 11.5 microg/mL for the different polyphenols. A good repeatability was obtained, with intra-day variations less than 7.9%. The described method was successfully applied to quantify several polyphenols in 26 samples of different kinds of wine (red, rosé and white wines) from Madeira and Canary Islands. Gallic acid was by far the most predominant acid. It represents more than 65% of all phenolics, followed by p-coumaric and caffeic acids. The major flavonoid found in Madeira wines was trans-resveratrol. In some wines, (-)-epicatechin was also found in highest amount. Canary wines were shown to be rich in gallic, caffeic and p-coumaric acids and quercetin.     

A new protocol to synthesize 1,4-dihydropyridines by using 3,4,5-trifluorobenzeneboronic acid as a catalyst in ionic liquid: synthesis of novel 4-(3-carboxyl-1H-pyrazol-4-yl)-1,4-dihydropyridines

3,4,5-Trifluorobenzeneboronic acid catalysed, ionic liquid mediated facile synthesis of 4-pyrazolyl 1,4-dihydropyridines at room temperature by the cyclocondensation of ethyl 3-aminocrotonate, pyrazole aldehyde and a β-keto ester is reported. The procedure adopted was found to be eco-benign, facile at room temperature and better than the conventional, [bmim]Cl mediated and InCl₃ catalysed, [bmim]Cl mediated 1,4-dihydropyridine syntheses.     

Electrochemical oxidation of C4-vanillin- and C4-isovanillin-1,4-dihydropyridines in aprotic medium: Reactivity towards free radicals

This work reports the electrochemical oxidation of two new synthetic C4-vanillin and -isovanillin-1,4-dihydropyridines in aprotic medium. Its reactivity with alkylperoxyl radicals ABAP-derived at pH 7.4 is also studied. Voltammetry, coulometry, controlled-potential electrolysis, UV–visible spectroscopy and GC–MS techniques were employed to collect data that permitted us to study its oxidation. Effect of TBA-OH addition on the oxidation was electrochemically and spectroscopically followed. In aprotic medium, the oxidation mechanism involves the formation of the pyridine derivative, which was generated by controlled-potential electrolysis (CPE) at 1270 mV and identified by GC–MS technique as the final product of the electrolysis. Spectroelectrochemical experiments also support the formation of the pyridine derivative from the oxidation of both 1,4-dihydropyridines. Direct reactivity of synthesized compounds towards alkylperoxyl radicals ABAP-derived was determined. Results reveal that the inclusion of vanillin radical or its positional isomer, isovanillin in the 4-position of the dihydropyridine ring produced a significant positive effect on the reactivity towards alkylperoxyl radicals, even compared with commercial dihydropyridine drugs with a well-known antioxidant ability. Scavenging mechanism involves the electron-transfer and the formation of a pyridine derivative, which was identified by GC–MS.     

对硝基甲苯合成3,4-二甲基苯胺的研究

以对硝基甲苯为原料,经胺甲基化、水解、还原3步反应合成了目标化合物。通过单因素实验,分析每一步反应的关键影响因素,初步得到适宜的合成条件。最终产物的结构经核磁氢谱、质谱、元素分析进行确证,纯度经气相色谱分析。3,4-二甲基苯胺的总收率56.6%,纯度大于98.5%。该合成路线原料易得,成本较低,操作简单。     

One-Pot Synthesis of N-Substituted 4-Aryl-1,4-dihydropyridines Under Solvent-Free Conditions and Microwave Irradiation

Summary.  The three-component condensation of benzaldehyde derivatives, alkyl propiolates, and primary amines catalyzed by silica gel, zeolite HY, montmorillonite K-10, and acidic alumina under microwave irradiation gave N-substituted 4-aryl-1,4-dihydropyridines in short reaction times and high yields. The best results were obtained with silica gel. Received March 26, 2001. Accepted (revised) June 18, 2001     

The unique regioselectivity in the formation of disubstituted-1,4-benzoquinones generated from the reaction of 4-hydroxycoumarins with 1,4-benzoquinone

The 2,3-disubstituted 1,4-benzoquinones were synthesized through the regioselective addition of 4-hydroxycoumarins with 1,4-benzoquinone in aqueous acetone, which were different from 2,5-disubstituted adducts generated by the previously reported reaction of compounds possessing an activated methylene with 1,4-benzoquinone.     

Electrochemical Conversions of 2-Methyl-3-nitro-4-phenylquinoline, Its Quinolinium Salts, and Hydrogenated Derivatives

Classical polarography, cyclic voltammetry, and EPR spectroscopy was used to study electrochemical reduction and oxidation of 3-nitro derivatives of 2-methyl-4-phenylquinoline, the corresponding quinolinium perchlorates, and 1,2- and 1,4-dihydroquinolines. The nitro derivatives of quinoline and 1,2-dihydroquinoline are reduced in the first step at the nitro group; the quinolinium cations are reduced at the heterocycle followed by reduction of the nitro group; and in 1,4-dihydroquinolines, the nitro group is not reduced. Electrochemical reduction processes associated with electron transfer in the heterocycle mainly display the same behavior as established for pyridine derivatives. But important differences were observed in electrochemical oxidation: the N-methyl derivative of 1,4-dihydroquinoline is oxidized significantly more easily than the corresponding N-unsubstituted derivative of 1,4-dihydroquinoline (in the 1,4-dihydropyridine series, the difference in pot! enti als is fairly small), and even more easily than the corresponding N-methyl derivative of 1,2-dihydroquinoline.     

4-Phenyl-1,2,4-triazole-3,5-dione as a novel and reusable reagent for the aromatization of 1,4-dihydropyridines under mild conditions

4-Substituted 1,3,4-triazole-3,5-diones were used as effective and recyclable oxidizing agents for the oxidation of 1,4-dihydropyridines to the corresponding pyridine derivatives under mild conditions with good to excellent yields.     

Synthesis of 2,5 -Bis(4-methyl-2-thienyl)thiophene and 2,5-Bis(4-methyl-2-thienyl)pyrrole

Syntheses of 2,5-bis(4-methyl-2-thienyl)thiophene 3 and 2,5-bis(4-methyl-2-thienyl)pyrrole 4 are described. The key step involves Stetter reaction between 4-methyl-2-thiophenecarboxaldehyde and divinyl sulfone. Cyclizaton of the resulting 1,4-bis-(4-methyl-2-thienyl)-1,4-butanedione 2 with Lawesson's reagent gives 2,5-bis(4-methyl-2-thienyl)thiophene 3, whereas condensation with ammonium acetate provides the 2,5-bis(4-methyl-2-thienyl)pyrrole 4.     

Reactions of cyclic enhydrazinoketones with arylidene derivatives of malononitrile. Synthesis of fusedN-substituted 1,4-dihydropyridines

A new method for the synthesis of fusedN-amino-1,4-dihydropyridines was proposed. The method is based on the addition of cyclic enhydrazinoketones to arylidenemalononitriles. The structures of the compounds synthesized were studied using¹H NMR spectroscopy. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1254–1257, July, 2000.     

Electrocarboxylation of 1,4-dibromobut-2-ene in a CO2-DMF liquid mixture

The possibility of synthesizing dihydromuconic acid by cathodic carboxylation of 1,4-dibromobut-2-ene in the liquid CO₂-aprotic solvent system was investigated. The low yield of dihydromuconic acid in this reaction was explained by the competing reductive debromodimerization and oligomerization of 1,4-dibromobut-2-ene, which lead to the predominant formation of 1,8-dibromo-2,6-octadiene and polymeric products. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1637–1641, September, 1997.     

(2R,4S)-4-甲基-2-哌啶甲酸乙酯的合成

以S-(-)-α-苯乙胺为原料,经一锅法制得1-(1-苄基)-6-乙氧羰基-4-甲基-3,4-二氢哌啶(3),收率58.7%。以10%Pd/C为催化剂,3经催化氢化脱苄合成了4-甲基-2-哌啶甲酸乙酯(4),收率96%;4通过减压分馏得(2R,4S)-4,含量95%,其结构经1H NMR,IR和MS确证。     

Magnetic Field Effects on Photoreduction Reaction of 2-Methyl-1,4-Naphthoquinone in Brij 35 Micellar Solution with Additional Radical

Introduction In the past three decades, many groups have been concerning and studying magnetic field effects (MFEs) on photoreduction reaction of carbonyl compounds such as benzophenone, benzoquinone and anthraquinone de-rivatives in micellar solutions. The radical pair lifetime and the escaped radical yield increased with the increase of magnetic field strength. The observed MFEs for these systems could be successfully explained by the relaxa-tion mechanism (RM), where the spin relaxation …     

以1,4-二甲基咔唑-9-丙酸为荧光衍生化试剂高效液相色谱法测定醇

1,4-二甲基咔唑-9-丙酸与间苯二磺酰氯反应生成混合酸酐,该混合酸酐能够衍生化18个碳以下的直链脂肪伯醇、6个碳以下的仲醇,以及叔丁醇和胆固醇;将荧光衍生物用反相C18液相色谱柱进行分离,在室温下10min完成衍生化反应,衍生物24h内基本稳定.基于此,建立了血清中醇的高效液相色谱测定方法.     

鸡肉中多种磺胺兽药残留量测定的高效液相色谱-电化学检测法

采用液相色谱电化学法测定了鸡肉中磺胺类药物残留量；磺胺用氯仿提取后，取部分提取液用氮气吹干，残渣溶于KH2PO4中，用正己烷脱脂，水相进样，液相色谱分析用C18柱，流动相为甲醇－0．01mol/L KH2PO4(pH6，体积比25：75），检测电位1．0V；与紫外检测器相比，电化学检测器（ECD）有更高的灵敏度和选择性，ECD的检出限为磺胺嘧啶0.02ng，磺胺甲氧哒嗪0．06ng，磺胺甲基异恶唑0.07ng。     

l-Ascorbic acid in organic synthesis: a facile synthesis of 4-(butenolide-5-methylidenyl)-1,4-dihydropyridines

An efficient synthesis of 4-(butenolide-5-methylidenyl)-1,4-dihydropyridines has been achieved via a three-component reaction of β-keto esters or ketones, ammonium acetate and vinylic aldehydes from ascorbic acid in the presence of tetrabutylammonium hydrogen sulfate in ethylene glycol.     

4-(10-Methyl-10H-phenothiazin-3-yl)-1,4-dihydropyridines, 4,5-dihydroindeno[1,2-<Emphasis Type="Italic">b</Emphasis>]-and 5,5-dioxo-4,5-dihydrobenzo-thieno[3,2-<Emphasis Type="Italic">b</Emphasis>]pyridines

Different modifications of the Hantzsch synthesis using 10-methyl-10H-phenothiazine-3-carbaldehyde gave 4-(10-methyl-10H-phenothiazin-3-yl)-substituted 1,4-dihydropyridine-3,5-di-, 5-oxo-4,5-dihydro-1H-indeno[1,2-b]pyridine-, and 5,5-dioxo-4,5-dihydro-1H-5λ⁶-benzo[4,5]thieno[3,2-b]pyridine-3-carboxylic esters. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 280–288, February, 2007.