α-羟醛的新合成方法研究

报道了一种制备α-羟醛的未见文献报道的合成方法, 以乙二胺和α-羟基羧酸为原料, 经咪唑啉中间体, 得到α-羟醛。讨论了反应条件、取代基对咪唑啉中间体还原水解反应产率的影响。     

Synthesis of deoxy sugar esters: a chemoenzymatic stereoselective approach affording deoxy sugar derivatives also in the form of aldehyde

A chemoenzymatic synthesis of deoxy sugar esters is described. The synthesis is based on the O-alkylation of carboxylic acid with 2-bromo-5-acetoxypentanal. The method allows treatment of hydroxy carboxylic acids without protection of alcoholic hydroxyl groups. Several stereoisomeric deoxy sugar esters were resolved (up to ee or de > 98%) using a lipase-catalyzed acetylation of hemiacetals that in certain cases afforded deoxy sugar derivatives in the form of aldehydes. The stereochemistry of the reactions was determined by the NMR spectra of mandelic acid derivatives.     

Enantioselective separation in capillary electrophoresis using a novel mono-6-propylammonium-β-cyclodextrin as chiral selector

The chiral resolving ability of a novel single-isomer cationic β-cyclodextrin (CD), mono-6^A-propylammonium-6^A-deoxy-β-cyclodextrin chloride (PrAMCD), as a chiral selector in capillary electrophoresis (CE) is reported in this work for the enantioseparation of hydroxy, carboxylic acids and amphoteric analytes. The effect of chiral selector concentration on the resolution was studied. Good resolutions were achieved for hydroxy acids. Optimum resolutions were obtained even at 3.5 mM CD concentration for carboxylic acids. The electrophoretic method showed good linearity and reproducibility in terms of migration times and peak areas, which should make it suitable for routine analysis. In addition, baseline chiral separation of a six-acid mixture was achieved within 20 min. PrAMCD proved to be an effective chiral selector for acidic analytes.     

Simultaneous determination of C2-C22 non-esterified fatty acids and other metabolically relevant carboxylic acids in biological material by gas chromatography of their benzyl esters

A method for the simultaneous determination of non-esterified short-, medium- and long-chain fatty acids and other types of metabolically relevant carboxylic acids such as hydroxy, keto, aromatic and dicarboxylic acids in biological material by capillary gas chromatography of benzyl ester derivatives is described. Sample preparation avoiding incomplete isolation of carboxylic acids consisted of deproteinization and extraction with ethanol, fixation of carboxylic acids as carboxylates, removal of interfering compounds such as neutral lipids by hexane extraction and amino acids, acyl carnitines and other cations by cation-exchange chromatography, derivatization of keto groups of ketocarboxylic acids into O-methyl oximes and benzyl ester formation by reaction of the potassium carboxylates with benzyl bromide via crown ether catalysis. The sample preparation conditions were investigated, showing the usefulness of this method for quantitative determinations. Chromatograms obtained from human serum, human urine and rat heart ventricle and concentrations of carboxylic acids in these specimens are presented.     

A comparison of negative and positive ion mass spectrometry

Negative ion mass spectrometry using a conventional mass spectrometer with a special ion source and a sample pressure of approximately 2 × 10^?5 Torr is shown to be an excellent method for the qualitative analysis of lower mass alcohols, mercaptans, ketones, aldehydes, aliphatic carboxylic acids and esters, the spectra of which are characterized by intense [M – H] ^? ions. The method may be termed a ‘selective’ low energy ionization technique, being suitable for the above organic compounds, but not for nitriles, nitro compounds, hydrocarbons, ethers, amines, amides, nitrogen heterocycles and chlorinated compounds. This method can be looked upon as a complementary method, to positive ion mass spectrometry.     

Efficient and Highly Selective Oxidation of Primary Alcohols to Aldehydes by N-Chlorosuccinimide Mediated by Oxoammonium Salts

2,2,6,6-Tetramethyl-1-piperidinyloxy catalyzes efficient oxidation of primary alcohols to aldehydes by N-chlorosuccinimide, in a biphasic dichloromethane-aqueous pH 8.6 buffer system in the presence of tetrabutylammonium chloride. Aliphatic, benzylic, and allylic alcohols are readily oxidized with no overoxidation to carboxylic acids. Secondary alcohols are oxidized to ketones with a much lower efficiency. Very high chemoselectivities are observed when primary alcohols are oxidized in the presence of secondary ones. Primary-secondary diols are selectively transformed into hydroxy aldehydes, with, in some cases, no detectable formation of the isomeric keto alcohols.     

Triflylpyridinium Enables Rapid and Scalable Controlled Reduction of Carboxylic Acids to Aldehydes using Pinacolborane

Building up new and efficient methods for the controlled conversion of carboxylic acids to aldehydes is important. Herein, we report a rapid, modular and scalable method for the conversion of carboxylic acids to aldehydes using pinacolborane at ambient temperature, in which a triflylpyridinium reagent is used. The conversion of carboxylic acid to intermediate acylpyridinium by triflylpyridinium is new. A binary pyridine-coordinated boronium complex is generated after reduction. The unprecedented reduction of the acylpyridinium by HBpin opens up a practically direct synthesis of aldehydes from carboxylic acids. Theoretical studies indicate that the reduction of acylpyridinium requires a lower activation free energy than that of the product aldehyde. The synthetic advantage of this protocol is further highlighted by the scalable synthesis of aldehyde via continuous flow process. Configuration retention for chiral acids are presented in those syntheses.     

A Novel Synthetic Method for the Preparation of Aliphatic Aldehydes from the Corresponding Carboxylic Acids

A novel synthetic method for the preparation of aliphatic aldehydes from the corresponding carboxylic acids via 1,3‐dimethylbenzimidazolium salts is provided. 1,3‐Dimethylbenzimidazolium salts were rapidly reduced with sodium/ethanol and then hydrolyzed with hydrochloric acid to obtain aliphatic aldehydes, in which the 1,3‐dimethylbenzimidazolium salts can be readily achieved from the corresponding carboxylic acids. The mechanism for the reductive reaction of 1,3‐dimethylbenzimidazolium salts with sodium/ethanol was discussed.     

An Enantio‐ and Diastereoselective Chemoenzymatic Synthesis of α‐Fluoro β‐Hydroxy Carboxylic Esters

The trans‐o‐hydroxybenzylidene pyruvate aldolase‐catalysed reactions between fluoropyruvate and many (hetero)aromatic aldehydes yield aldol adducts without subsequent dehydration. Treatment of the reaction products with hydrogen peroxide yields the corresponding syn‐configured α‐fluoro β‐hydroxy carboxylic acids which have >98 % ee. The overall chemoenzymatic approach, in which fluoropyruvate serves as a fluoroacetate equivalent, may be exploited in the synthesis of polar building blocks and fragments with potential value in drug discovery.     

Aerobic oxidation of aldehydes by visible light photocatalysis

An efficient and environmentally benign method for the oxidation of aldehydes to carboxylic acids has been developed. Singlet oxygen, generated by visible light in the presence of a Ru or Ir photocatalyst, reacted with aldehydes to give the corresponding carboxylic acids in excellent yields. The reaction is highly chemo-selective, in which only an aldehyde moiety is reactive even in the presence of other photo-oxidation active sites. This method is an example of an ideal green chemical reaction in the sense that molecular oxygen and visible light are key sources for the transformation.     

Pentaatomie heteroaromatic cations. Note III . A Convenient Synthesis of Aldehydes from Carboxylic Acids via 2-Substituted 1,3-Benzoxathiolium Perchlorates

A convenient method for the preparation of aldehydes from the corresponding carboxylic acids is presented. By reaction of the carboxylic acids with o-mercaptophenol and perchloric acid in phosphorus oxychloride, the corresponding 2-substituted 1,3-benzoxathiolium perehlorates were obtained. Reduction of the salts with lithium aluminium hydride in dry ether gave 2-substituted 1,3-benzoxathioles, which, when hydrolyzed by mercuric chloride, gave the corresponding aldehydes. Twenty five aldehydes of different structure were obtained in good yields, by a fast and simple procedure.     

An Improved Procedure for the Conversion of Carbonyl Compounds to α,β-Unsaturated Carboxylic Acids

The two carbon homologation of aldehydes and ketones to give α,β-unsaturated carboxylic acids is often carried out via the corresponding ester using metallated phosphonate reagents² (1) (Equation I). When alkyl esters (la) are employed problems are sometimes encountered in the hydrolysis step due to acid or base sensitivity but these problems can be overcome using the silyl ester (lb)³.     

Identification of carbonyl species of weathered LDPE films by curve fitting and derivative analysis of IR spectra

We describe the examination of the weathering degradation of LDPE (low density polyethylene - locally produced B24/2 and imported LDPE 2100T), supplied by two different manufacturers and processed into films for greenhouse coverings, over several months in a sub-Saharan region of Algeria. The three IR regions most affected by weathering degradation are 800–1100 cm⁻¹, 1680–1800 cm⁻¹ and 3300–3600 cm⁻¹. The IR spectral region most affected by the aging process is the carbonyl region. Curve fitting combined with derivative spectroscopy revealed that the composite carbonyl band encompasses more than 10 different oxidation products. The most significant among these in terms of absorbance are carboxylic acids, ketones, aldehydes and esters. The oxidation kinetics with respect to the type of LDPE film shows that B24/2 LDPE undergoes less oxidization than LDPE 2100 T. Calculating the concentrations of different carbonyl species compared to their respective absorbances indicates that the aldehydes are the predominant component of the final compound, rather than the carboxylic acids.     

Facile Oxidation of Aldehydes to Carboxylic Acids with Chromium(V) Reagents

Recently we reported a convenient method of oxidation of alcohols to carbonyl compounds using chromium(V) reagents.¹ Although a variety of reagents are available for effecting this transformation, there are only a few reagents which have been successfully used for the oxidation of aldehydes to carboxyllc adds. Chromic acid, silver oxide and potassium permanganate are commonly employed for this purpose and reactions are performed in protic media under conditions which are not that mild.² The “non-aqueous” chromium(VI) reagent, pyridinium dichromate, recently reported by Corey³ oxidises alcohols and aldehydes to carboxylic acids in DMF at room temperature. Although Cr(V) species is postulated as an intermediate in all oxidations with Cr(VI), no systematic oxidation studies have been reported with these reagents. This note reports the results of some fruitful investigations on aldehyde → carboxylic acid conversion involving some “non-aqueous” chromium (V) complexes 1, 2, 3 and 5 under anhydrous conditions.     

Efficient allylation of aldehydes promoted by carboxylic acids

A variety of carboxylic acids have been screened for mediating the allylation of aldehydes with allytributyltin in different solvents. A novel, general, and practical method of allylation of aldehydes promoted by carboxylic acids under mild reaction conditions has been developed. Among them, p-nitrobenzoic acid afforded high to quantitative yields of the homoallylic alcohol products, and can be easily recovered after workup by aqueous HCl. Glyoxylic acid self-catalyzed the allylation without adding any other promoter or catalyst to give the corresponding allylation product in good yield. The regioselectivity of the crotylation of aldehydes is tunable by controlling the acidity of the carboxylic acids. The crotylation of aldehydes produced the alpha-adduct as major products in moderate to good yields with CF(3)CO(2)H as a promoter. A possible mechanism for the allylation is also discussed.     

Oxidative decarboxylation of arylacetic acids in water: One-pot transition-metal-free synthesis of aldehydes and ketones

One-pot transition-metal-free synthesis of aromatic aldehydes and ketones via oxidative decarboxylation of arylacetic acids in water is developed. Protocol relies on the direct decarboxylation of sp³-hybridized carbon in water without any over oxidation into carboxylic acids with minimal waste. Reaction mechanism is investigated and application of this protocol is demonstrated on a gram scale.     

On-line determination of carboxylic acids, aldehydes and ketones by high-performance liquid chromatography-diode array detection-atmospheric pressure chemical ionisation mass spectrometry after derivatization with 2-nitrophenylhydrazine

2-Nitrophenylhydrazine (2-NPH) is widely used for the derivatization of carboxylic acids, aldehydes and ketones, in industrial and biological samples. These compounds react with 2-NPH to form derivatives, which are separated by high-performance liquid chromatography (HPLC) and detected with diode array detection (DAD). The UV spectra give information about the functionality of the compounds: carboxylic acid or ketone/aldehyde. Most of the eluting compounds in "known" samples are well characterised by the retention time (comparison with those of standards) of the 2-NPH derivative and their UV spectrum. The identification of different unknown 2-NPH derivatives of carboxylic acids, ketones and/or aldehydes, in industrial or biological samples, based on retention time and/or UV spectrum is not sufficient. These unknown 2-NPH compounds can be identified with on-line atmospheric pressure chemical ionisation mass spectrometry (APCI-MS) based on the molecular mass or/and the fragmentation of the derivative. A novel and specific on-line HPLC-DAD-APCI(-)-MS method is described for the determination of carboxylic acids, ketones and aldehydes, after on-line pre-column derivatization with 2-NHP. The fragmentation of different 2-NPH derivatives were investigated and the possibilities of APCI(-)-MS detection were demonstrated by the on-line identification of an unknown derivative, which turned out to be a side product between 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 2-NPH in the presence of high concentrations of a cyclic amide in the sample solution.     

Selective oxoammonium salt oxidations of alcohols to aldehydes and aldehydes to carboxylic acids

The oxidation of alcohols to aldehydes using stoichiometric 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) in CH(2)Cl(2) at room temperature is a highly selective process favoring reaction at the carbinol center best able to accommodate a positive charge. The oxidation of aldehydes to carboxylic acids by 1 in wet acetonitrile is also selective; the rate of the process correlates with the concentration of aldehyde hydrate. A convenient and high yield method for oxidation of alcohols directly to carboxylic acids has been developed.     

Barium Manganate Oxidation in Organic Synthesis: Part—IV: Oxidation of Aldehydes to Carboxylic Acids

The oxidation of aldehydes to corresponding carboxylic acids by barium manganate under heterogeneous conditions is described. Aromatic aldehydes were smoothly converted to carboxylic acids while aliphatic aldehydes underwent polymerisation.     

Analysis of α‐acyloxyhydroperoxy aldehydes with electrospray ionization–tandem mass spectrometry (ESI‐MSn)

A series of α‐acyloxyhydroperoxy aldehydes was analyzed with direct infusion electrospray ionization tandem mass spectrometry (ESI/MSⁿ) as well as liquid chromatography coupled with the mass spectrometry (LC/MS). Standards of α‐acyloxyhydroperoxy aldehydes were prepared by liquid‐phase ozonolysis of cyclohexene in the presence of carboxylic acids. Stabilized Criegee intermediate (SCI), a by‐product of the ozone attack on the cyclohexene double bond, reacted with the selected carboxylic acids (SCI scavengers) leading to the formation of α‐acyloxyhydroperoxy aldehydes. Ionization conditions were optimized. [M + H]⁺ ions were not formed in ESI; consequently, α‐acyloxyhydroperoxy aldehydes were identified as their ammonia adducts for the first time. On the other hand, atmospheric‐pressure chemical ionization has led to decomposition of the compounds of interest. Analysis of the mass spectra (MS² and MS³) of the [M + NH₄]⁺ ions allowed recognizing the fragmentation pathways, common for all of the compounds under study. In order to get detailed insights into the fragmentation mechanism, a number of isotopically labeled analogs were also studied. To confirm that the fragmentation mechanism allows predicting the mass spectrum of different α‐acyloxyhydroperoxy aldehydes, ozonolysis of α‐pinene, a very important secondary organic aerosol precursor, was carried out. Spectra of the two ammonium cationized α‐acyloxyhydroperoxy aldehydes prepared with α‐pinene, cis‐pinonic acid as well as pinic acid were predicted very accurately. Possible applications of the method developed for the analysis of α‐acyloxyhydroperoxy aldehydes in SOA samples, as well as other compounds containing hydroperoxide moiety are discussed. Copyright © 2013 John Wiley & Sons, Ltd.