Synthesis of substituted esters of imidazoles,oxazoles, thiazoles,and diethyl pyrazine-2,5-dicarboxylate from a common acyclic precursor employing C-formylation strategy

A novel synthetic route to substituted esters of imidazoles, oxazoles, thiazoles, and diethyl pyrazine-2,5-dicarboxylates via C-formylation of glycine ethyl ester hydrochloride is reported. This methodology is simple, robust, and gives good yields of different heterocyclic esters in one or two steps from a common acyclic precursor and is amenable to large scale synthesis.     

REACTION BETWEEN 2-HYDROXY ESTERS OF HYPOPHOSPHOROUS ACID AND ALCOHOLS

Abstract

A study of the reaction between esters of hypophosphorous acid and alcohols is carried out. It has been established that the 2-hydroxy esters of hypophosphorous acid react with alcohols as a result of which phosphonous acids are formed. A possible scheme of this reaction is suggested.     

同位素稀释-气相色谱-质谱法测定食用植物油中总氯丙醇脂肪酸酯

建立了食用植物油中总氯丙醇脂肪酸酯(氯丙醇酯)的同位素稀释-气相色谱-质谱(GC-MS)检测方法。样品经甲醇钠-甲醇溶液水解,硅藻土小柱净化,七氟丁酰咪唑(HFBI)衍生后,GC-MS 检测,同位素内标法定量。3-MCPD 酯、2-MCPD 酯、1,3-DCP 酯和2,3-DCP 酯在0.050~2.000 mg/ L 浓度范围内,均呈良好线性相关,相关系数(R)均大于0.9995。3-MCPD 酯、2-MCPD 酯、1,3-DCP 酯和2,3-DCP 酯的检出限分别为0.015,0.015,0.030和0.030 mg/ kg,定量限分别为0.050,0.050,0.100和0.100 mg/ kg。以空白特级初榨橄榄油为空白基质的加标回收实验的平均回收率为87.0%~110.5%,相对标准偏差(RSD)均小于10.1%。在74份食用植物油样品中,3-MCPD 酯、2-MCPD 酯和1,3-DCP 酯的检出率分别为94.6%,63.5%和5.4%,未检出2,3-DCP 酯;3-MCPD 酯、2-MCPD 酯和1,3-DCP 酯的含量分别在未检出(ND)~10.646 mg/ kg、ND ~3.617 mg/ kg 和ND ~0.089 mg/ kg 之间。本方法简便、准确、可靠,适用于食用植物油中总氯丙醇酯的测定。     

Unnatural amino acids. 3. Aziridinyl ketones from esters and amides of aziridine-2-carboxylic acids

A series of N-substituted amides and esters of aziridine-2-carboxylic acids have been prepared and have been subjected to deprotonation with lithium diisopropylamide. The intermediate carbanions reacted more readily with the carbonyl groups of the substrates than with methyl iodide. So, in place of the expected amides or esters of methylaziridine-2-carboxylic acids, amides or esters of 2-aziridinylcarbonylaziridine-2-carboxylic acids were isolated. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, 220–225, February, 2007.     

GC–MS analysis of phenolic compounds in fuels after conversion to trifluoroacetate esters

The GC–MS characteristics of trifluoroacetate esters of phenolic compounds are discussed. Linear temperature programmed retention indices and total ion current MS response factors of over 120 phenolic esters are reported. The main GC advantages from analysis of trifluoroacetate esters as compared to plain phenols are enhanced volatility and improved resolution. For example, the elution temperature of a given phenol is typically 50 °C greater than that of the corresponding trifluoroacetate ester. Also, while retention of compounds with two trifluoroacetate groups is only moderately greater than mono esters, underivatized dihydroxy compounds are very difficult to elute from any GC column. Complete resolution of isomeric C₀-, C₁- and C₂-alkylphenol esters is readily achieved on conventional fused silica GC columns; resolution of the corresponding underivatized compounds requires specialized GC columns with low temperature limits. In general, mass spectra of trifluoroacetate esters are more characteristic of a given structure than those of the corresponding phenols and may be more rigorously interpreted towards structural elucidation. A table in the report summarizes some of the more important spectral features used in compound identification. Example applications in analysis of coal-, shale- and petroleum-derived materials are presented. Selected ion monitoring is used to determine individual phenolic components in whole distillates; reconstructed ion chromatograms are used to illustrate distributions of selected species as a function of fuel storage and thermal stress.     

Unnatural Amino Acids. 2. Simple Method of Obtaining Esters of Aziridine-2-carboxylic Acids by a Transesterification Reaction

A series of N-unsubstituted esters of aziridine-2-carboxylic acid has been obtained by transesterification in basic medium using primary, secondary, and tertiary alcohols. Methods of transesterification using various bases (K₂CO₃, ROLi, t-BuOK) have been compared. Transesterification with lithium alcoholates also affords the possibility of obtaining esters of N-substituted aziridine-2-carboxylic acids. Transesterification of chiral esters proceeds with retention of the configuration of the chiral center.     

大口径毛细管气相色谱法在甲基丙烯酸特种酯合成中的应用

 用大口径毛细管气相色谱法对甲基丙烯酸特种酯合成反应液中的各组分进行了分离分析鉴定。色谱柱 :高惰性交联SE 5 4大口径石英弹性毛细管柱 ,5 0m× 0 5 3mmi d × 0 6 μm。主组分回收率为 99 71%～ 10 2 89%,相对标准偏差小于 0 1%,可作为甲基丙烯酸特种酯类生产控制的一种实用方法。     

Microwave-Assisted Esterification of Diverse Carboxylic Acids and Chiral Amino Acids

A facile and efficient synthetic method of esters from their corresponding carboxylic acids and amino acids is described. The esterification reaction of carboxylic acids and amino acids could be greatly accelerated under microwave irradiation because the reactions described in this article took place in only 5 min with almost quantitative yields, and distinct acidity of catalytic acids was well tolerated. Unlike the racemation problem in microwave-assisted N-acylation reactions, the esters of chiral amino acids could be achieved with retention of configuration under this condition.     

Nukleophile Substanzen zur Entgiftung von Phosphorestern

A series of N-substituted hydroxylamine derivatives was synthesized as a potential substitute for calcium hypochlorite. Like calcium hypochlorite, these compounds are highly P(V)-nucleophilic with respect to toxic phosphorus esters.Incorporating surface-active structural elements into the compounds can enhance their reactivity to phosphorus esters on the one hand (micelle catalysis); on the other hand aqueous solutions of these compounds wet polymer surfaces easily, thus ensuring that they can be well applied. The effectiveness of the compounds in the detoxification of phosphorus esters was examined using diisopropyl fluorophosphate (DFP) as a model substance.

     

油脂性食品中脂肪酸氯丙醇酯检测方法的研究进展

脂肪酸氯丙醇酯污染是近年来国际上新出现的热点食品安全问题之一,尤其是3-氯-1,2-丙二醇脂肪酸酯(3-MCPD酯)污染问题更为突出。3-MCPD酯在食用油、婴幼儿奶粉等多种食品中的含量较高,以3-MCPD的最大耐受剂量(TDI)评估时所引起的健康风险较高。国外已对3-MCPD酯等氯丙醇酯的检测方法、污染调查和形成机制等开展了不少的研究,国内开展的研究较少。本文主要对油脂食品中3-MCPD酯的检测方法(包括前处理过程,如3-MCPD酯的提取、水解和衍生)、3-MCPD酯总量以及3-MCPD单酯和双酯的检测方法进行了综述。     

Analytical utility of 2-halopyridinium salts,part III paper electrophoretic characterization of alcohols as 2-alkoxy-1-methylpyridinium p-toluenesulphonates

Summary A method using high-voltage paper electrophoresis to separate 2-alkoxy-l-methylpyridinium p-toluenesulphonates derived from alcohols is described. Various primary and secondary alcohols are characterized by the relative mobilities of the corresponding 2-alkoxyl-l-methylpyridinium cations using orthoboric acid-orthophosphoric acid-ethylene glycol buffer as electrolyte. The method proved to be useful for the detection and identification of alcohols present as impurities in solvents. A procedure is outlined that permits identification of the alkoxy groups of esters. The procedure utilizes the alkaline hydrolysis of esters, reaction of the alcohols so formed with 2-fluoro-1-methylpyridinium p-toluenesulphonate followed by electrophoresis of the derived 2-alkoxy-1-methylpyridinium p-toluenesulphonates. Nanomole quantities of the separated compounds have been made detectable on the pherograms using Dragendorff's reagent.Part II, Ref. [1]     

Preparation of azidoaryl- and azidoalkyloxazoles for click chemistry

A series of azidoaryl- and azidoalkyl(diphenyl)oxazole scaffolds were warranted for biofilm inhibition studies. Cyclization of azidoaryl- or azidoalkyl esters of benzoin with ammonium acetate in acetic acid gives 2-azidoaryl- or 2-azidoalkyl-4,5-diphenyloxazoles. The azidoaryl esters are prepared from the corresponding azidocarboxylic acids/acid chlorides while the azidoalkyl esters are prepared from the corresponding haloalkyl esters.     

Gallium Trihalide Catalyzed Sequential Addition of Two Different Carbon Nucleophiles to Esters by Using Silyl Cyanide and Ketene Silyl Acetals

A sequential addition of silyl cyanide and ketene silyl acetals to esters was achieved by a gallium trihalide catalyst to produce β‐cyano‐β‐siloxy esters. This is the first example of the sequential addition of two different carbon nucleophiles to esters. The employment of lactones provided α,α‐disubstituted cyclic ethers with a cyano group and an ester moiety. A variety of esters and lactones are applicable to this reaction system.     

Preparation and aluminum trichloride-induced cationic rearrangements of bicyclo[2.2.0]hexene carboxylic esters

Reaction between the tetramethyl[4]annulene aluminum trichloride σ-complex and α, β-alkenic esters gave the corresponding 1,4,5,6-tetramethylbicyclo[2.2.0]hex-5-one-2-endo-carboxylic esters. AlCl₃-induced cationic rearrangements of these bicyclic esters yielded a number of bicyclo[3.1.0]hexene carboxylic esters and related lactones which were isolated and identified. The isomerization seems to proceed via stereospecific endo protonation and subsequent rearrangement to 2-methoxycarbonyl-1,4,5,6-exo-tetramethylbicyclo(3.1.0]hex-4-yl carbocations.     

A visible-light-promoted cross-dehydrogenative-coupling reaction of N-arylglycine esters with imidazo[1,2-a]pyridines

A mild and convenient visible-light-promoted cross-dehydrogenative-coupling reaction between N-arylglycine esters and imidazo[1,2-a]pyridines for the construction of CC bond was developed. A range of N-arylglycine esters and imidazo[1,2-a]pyridines were able to undergo the CDC reaction readily to afford α-heteroaryl substituted α-amino acid derivatives in good to excellent yields. A tentative mechanism for the photoredox reaction was also proposed. Importantly, the use of copper(II) salt as the sole catalyst in this visible-light-promoted transformation makes this reaction sustainable and practical.     

<Emphasis Type="Italic">S</Emphasis>-cinnamyl esters of thiocarbonic acids as additives to lubricating oils

A series of cinnamul esters of xanthic, trithiocarbonic, and dithiocarbamic acids were prepared. The optimal conditions of their synthesis were found. The cinnamyl esters were studied by thermal analysis, and the dependence of their lubricating power on the composition and structure was revealed. The tribological properties of lubricating oils with additions of cinnamyl esters of thiocarbonic acids were studied. A correlation between the structure of the esters synthesized and their antiscuff properties was found.     

Lipases in beta-dipeptide synthesis in organic solvents

A number of beta-dipeptides were prepared by two-step lipase-catalyzed reactions where N-acetylated beta-amino esters were first activated as 2,2,2-trifluoroethyl esters with Candida antarctica lipase B (CAL-B). The activated esters were then used to acylate beta-amino ester in the presence of Candida antarctica lipase A (CAL-A) in dry Et2O or i-Pr2O. [reaction: see text].     

Practical selective monohydrolysis of bulky symmetric diesters

The highly efficient selective monohydrolysis reaction we previously reported has been applied to monohydrolysis of several bulkyl symmetric diesters, including diethyl esters, dipropyl esters, and dibutyl esters. A greater proportion of a polar aprotic co-solvent, DMSO, and aqueous KOH appear to help improve the reactivity of bulky diesters compared to the corresponding dimethyl esters. The procedure is mild and practical, yielding the corresponding half-esters in high yields under simple conditions.     

Propanolysis of Esters Using Chlorotrimethylsilane

A variety of methyl esters are converted into the corresponding propyl esters upon treatment with l-propanol and chlorotrimethylsilane. Among them acyclic aliphatic esters have the best conversion rate.     

1-(2,4,6-triisopropylphenyl)ethylamine: a new chiral auxiliary for the asymmetric synthesis of gamma-amino acid derivatives

The title compound has proven to be an excellent chiral auxiliary for nitrones in SmI2-mediated reductive coupling with alpha,beta-unsaturated esters. A variety of such nitrones, prepared from aldehydes and enantiopure N-hydroxy-1-(2,4,6-triisopropylphenyl)ethylamine, afforded gamma-N-hydroxyamino esters in high yields and diastereomeric purity. These adducts, readily available as either enantiomer, could be transformed into gamma-N-acetoxyamino esters, N-Boc-gamma-amino esters, and gamma-lactams.