γ-Hydroxy-α,β-acetylenic esters:asymmetric syntheses and applications

γ-Hydroxy-α,β-acetylenic esters are versatile synthetic precursors to many organic compounds.This paper reviews the synthesis of chiral γ-hydroxy-α,β-acetylenic esters by asymmetric reduction of γ-oxo-α,β-acetylenic esters,enantioselective addition to aldehydes in the presence of chiral catalysts,and diastereoselective addition to chiral aldehydes.The preparation of racemic γ-hydroxy-α,β-acetylenic esters is also included.Examples are provided for the application of γ-hydroxy-α,β-acetylenic esters in organi...     

γ-Hydroxy-α,β-acetylenic esters: asymmetric syntheses and applications

γ-Hydroxy-α,β-acetylenic esters are versatile synthetic precursors to many organic compounds. This paper reviews the synthesis of chiral γ-hydroxy-α,β-acetylenic esters by asymmetric reduction of γ-oxo-α,β-acetylenic esters, enantioselective addition to aldehydes in the presence of chiral catalysts, and diastereoselective addition to chiral aldehydes. The preparation of racemic γ-hydroxy-α,β-acetylenic esters is also included. Examples are provided for the application of γ-hydroxy-α,β-acetylenic esters in organic synthesis.     

A facile entry to β,δ-diketo and syn-β,δ-dihydroxy esters

Reaction of N-methoxy-N-methyl amides with the dianions of acetoacetates gives β,δ-diketo esters in yields of synthetic use, and the diketo esters were selectively reduced to syn-β,δ-dihydroxy esters, key intermediates of synthetic HMG-CoA reductase inhibitors.     

Stereoselective cycloaddition of N-acyliminium cations withα,β-unsaturated ketones and esters

The cycloaddition of N-acyliminium cations with some deactivated alkenes such asα,β-unsaturate ketones and esters has been investigated.In most cases,the N-acyliminium cations produced from 3-hydroxy-2-arylisoindol-1-ones in the presence of BF_3·OEt_2 could be reacted withα,β-unsaturated ketones and esters to afford stereoselectively the cycloaddition products 6-acylisoindolo[2,1-a] quinolin-11-ones in moderate to high yields.     

Synthesis of alkylN-(α-amidomethyl)glycinates from glycine esters,aroylamides, and formaldehyde

A one-step synthesis of alkylN-(-amidomethyl)glycinates from glycine esters or their salts, formaldehyde, and aroylamides was developed. The effect of the structure of the amide component and the reaction conditions on the yields of the products was investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1078–1080, June, 1994.     

Polarity and structure of α-nitrocinnamic acid esters

Polarity and structure of ethyl α-nitrocinnamates have been studied by means of dipole moments method and quantum-chemical calculations. These compounds exist in the form of Z-isomers in solution, that is, nitro group and benzene ring are cis-positioned.     

Merging domino and redox chemistry: stereoselective access to di- and trisubstituted β,γ-unsaturated acids and esters

Merging is the game! The coupling of a domino reaction and an internal neutral redox reaction constitutes an excellent manifold for the stereoselective synthesis of di- and trisubstituted olefins featuring a malonate unit, an ester, or a free carboxylic acid as substituents at the allylic position (see scheme; MW=microwave). The reaction utilizes simple starting materials (propargyl vinyl ethers), methanol or water as solvents, and a very simple and bench-friendly protocol.     

Chemoselective conversion of α-unbranched aldehydes to amides, esters, and carboxylic acids by NHC-catalysis

Depending on the N-heterocyclic carbene catalyst utilized, α-unbranched aldehydes selectively provided amides, esters, or carboxylic acids through oxidation by NCS. The α-unbranched aldehyde underwent these reactions chemoselectively in the presence of an aromatic or α-branched aldehyde.     

Liquid–liquid equilibria for mixtures containing water,methanol, fatty acid methyl esters,and glycerol

The liquid–liquid equilibrium (LLE) data, including tie-lines and phase boundaries, were measured for the ternary systems of water + methanol + methyl oleate, water + methanol + methyl linoleate, glycerol + methanol + methyl oleate, and glycerol + methanol + methyl linoleate at temperatures from 298.2 K to 318.2 K under atmospheric pressure. All the LLE data follow the Othmer-Tobias equation. Each ternary system behaves type-I LLE. The areas of two-liquid coexistence region decrease with increasing temperature. The experimental data were applied to test the validity of the UNIFAC model and its modified versions, including UNIFAC-LLE and UNIFAC-Dortmund. The LLE data were also correlated with the NRTL and the UNIQUAC models. The UNIQUAC model yielded better results.     

Cyclic acetal formation between 2-pyridinecarboxyaldehyde and γ-hydroxy-α,β-acetylenic esters

A new transformation between 2-pyridinecarboxyaldehyde and γ-hydroxy-α,β-acetylenic esters to form highly functionalized cyclic acetals was discovered. This transformation proceeds under very mild conditions without any additives and is promoted by the basic nature of the pyridine ring.     

Catalytic asymmetric chloroamination reaction of α,β-unsaturated γ-keto esters and chalcones

Highly efficient catalytic chloroamination reaction of α,β-unsaturated γ-keto esters and chalcones has been developed via a chloronium-based mechanism to deliver anti-regioselective vicinal chloroamines instead of the aziridinium intermediates delivered aminochlorides. The combination of TsNCl(2) and TsNH(2) as reagents made the transformation highly efficient, delivering the γ-carbonyl-β-chloro-α-amino acid derivatives and α-chloro-β-amino-ketone derivatives in nearly quantitative yields with up to 99% ee and 99:1 dr under 0.05-0.5 mol % catalyst loading. TsNHCl was demonstrated to act as the key reactive species to form a bridged chloronium ion intermediate in the presence of a chiral scandium complex. The method might provide useful information for further realization of other haloamination reactions.     

Comparison of electrospray ionization and atmospheric pressure chemical ionization for multi-residue analysis of biocides,UV-filters and benzothiazoles in aqueous matrices and activated sludge by liquid chromatography–tandem mass spectrometry

This paper describes the development of a multi-residue method for the determination of 36 emerging organic pollutants (26 biocides, 5 UV-filters and 5 benzothiazoles) in raw and treated wastewater, activated sludge and surface water using liquid chromatography–tandem mass spectrometry (LC–MS/MS). The target analytes were enriched from water samples adjusted to pH 6 by solid-phase extraction (SPE) on Oasis HLB 200 mg cartridges and eluted with a mixture of methanol and acetone (60/40, v/v). Extraction of freeze-dried sludge samples was accomplished by pressurized liquid extraction (PLE) using a mixture of methanol and water (50/50, v/v) as extraction solvent followed by SPE. LC–tandem MS detection was compared using electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in positive and negative ionization mode. ESI exhibited strong ion suppression for most target analytes, while APCI was generally less susceptible to ion suppression but partially leading to ion enhancement of up to a factor of 10. In general, matrix effects could be compensated using stable isotope-labeled surrogate standards, indicated by relative recoveries ranging from 70% to 130%. In wastewater, activated sludge and surface water up to 33 analytes were detected. Maximum concentrations up to 5.1 and 3.9 μg L⁻¹ were found in raw wastewater for the water-soluble UV-filters benzophenone-4 (BZP-4) and phenylbenz-imidazole sulfonic acid (PBSA), respectively. For the first time, the anti-dandruff climbazole was detected in raw wastewater and in activated sludge with concentrations as high as 1.4 μg L⁻¹ and 1.2 μg g TSS⁻¹, respectively. Activated sludge is obviously a sink for four benzothiazoles and two isothiazolones, as concentrations were detected in activated sludge between 120 ng g TSS⁻¹ (2-n-octyl-4-isothiazolin-3-one, OIT) to 330 ng g TSS⁻¹ (benzothiazole-2-sulfonic acid, BTSA).     

Correlation between structure and stability of nitronic acids and nitronic esters

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Microbial bioreductions of γ- and δ-ketoacids and their esters

A series of yeasts were used in the bioreductions of aliphatic and aromatic γ- and δ-ketoacids and esters to investigate the preparation of enantiomerically pure γ- and δ-lactones through the intermediacy of their corresponding γ- and δ-hydroxyacids and esters. Bioreduction of ethyl 4-oxononanoate 2a with Pichia etchellsii afforded the γ-nonanolide (+)-5a with 99% e.e., while Pichia minuta proved to be the best choice for the bioreduction of ethyl 2-oxocyclohexylacetate 2e, which afforded cis-(−)-5e and trans-(−)-5e with 98 and 99% e.e., respectively. Reduction of 3-(2-oxocyclohexyl)propionic acid 3e with Pichia glucozyma gave predominantly the corresponding δ-lactone trans-(−)-6e with 94% e.e., whose absolute configuration was determined by means of CD spectroscopy.     

Iron-catalyzed δ-selective conjugate addition of methyl and cyclopropyl Grignard reagents to α,β,γ,δ-unsaturated esters and amides

Iron-catalyzed δ-selective conjugate addition of methyl and cyclopropyl Grignard reagents to α,β,γ,δ-unsaturated esters and amides took place in good yields to give products exclusively with cis-β,γ-olefinic bond.     

Analysis of ancient Greco–Roman cosmetic materials using laser desorption ionization and electrospray ionization mass spectrometry

Microsamples of pink cosmetic powders from the Greco–Roman period were analyzed using two complementary analytical approaches for identification of the colouring agents (lake pigments originally manufactured from madder plants with an inert binder, usually a metallic salt) present in the samples. The first technique was a methanolic acidic extraction of the archaeological samples with an additional ethyl acetate extraction of the anthraquinone-type colouring agents which were identified using high performance liquid chromatography coupled to electrospray ionization with high resolution mass spectrometry (LC–ESI–HRMS), and the second was direct analysis of a microsample by laser desorption ionization–mass spectrometry (LDI–MS). The latter technique is well suited when the quantity of samples is very low. This soft ionization technique enables the detection of very small quantities of compounds using the combination of positive and negative-ion modes. It was also successfully applied for the direct analysis of some laboratory-made reference compounds. However, the presence of lead in one of these ancient samples induced a spectral suppression phenomenon. In this case and conditional on a sufficient quantity of available sample, the former method is better adapted for the characterization of these anthraquinone-type molecules. This study also confirmed that purpurin, munjistin, and pseudopurpurin are the principal colouring agents present in these ancient cosmetic powders constituted from madder plants. Presented at the Annual French National Symposium on Mass Spectrometry, Electrophoresis and Proteomics, 20–23 September 2007 in Pau, France.     

Copper complexes formed by 3,5-bis(2,2′-bipyridin-4-ylethynyl)benzoic acid and its methyl and ethyl esters as studied by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry was used to study the complexes of ligands containing two bipyridine units, namely 3,5-bis(2,2-bipyridin-4-ylethynyl)benzoic acid (1) and its methyl and ethyl esters (2, 3), with copper cation, with CuCl₂ as a source of copper. It was found that the type of complexes formed strongly depends on CuCl₂ concentration. At lower CuCl₂ concentration, the detected complexes were rather simple and some of them were formed upon electrospray ionization conditions e.g. ions [2₂+Cu₂]²⁺ and [3₂+Cu₂]²⁺ (complexes ligand-Cu(I) of stoichiometry 2:2) which are analogical to the well known, for quaterpyridine, helical complexes. At higher CuCl₂ concentration, the detected complexes were more complicated, and most of them contained copper cations bridged by chlorides. The largest ions were [L₂+Cu₄Cl₆]²⁺. The CID MS/MS spectra of these ions allowed determination of their mass spectrometric fragmentation pathways and as a consequence their structure elucidation.