Reduction microbiologique d'aldehydes α, β-ethyleniques par Beauveria sulfurescens

αβ-unsaturated aldehydes are reduced by Beauveriasulfurescens, giving a mixture of the corresponding ethylenic and saturated alcohols. Optically active saturated alcohols have the (S)-configuration.     

Cob(I)alamin als Katalysator. 1. Mitteilung. Reduktion von gesättigten Nitrilen in wässeriger Lösung

Co(I)alamin as Catalyst. 1. Communication. Reduction of Saturated Nitriles in Aqueous Solution Using cob(I)alamin as homogeneous catalyst in the presence of aqueous acetic acid saturated nitriles 5a – m are reduced to the corresponding aldehydes 6a – m in good yields. A possible reaction mechanism for this reduction is discussed.     

Chemoselective hydrogenation of α,β-unsaturated aldehydes with modified Pd/C catalyst

Selective hydrogenation of α, β-unsaturated aldehydes with modified Pd/C catalyst was developed.The reduction of C=O bond could be efficiently inhibited by the addition of carbonates,and high selectivity to the corresponding saturated aldehydes was achieved under mild conditions.This protocol provides an alternative for efficient preparation of saturated aldehydes.     

Selective 1,4-reduction of unsaturated carbonyl compounds using Co2(CO)8-H2O

α,β-Unsaturated ketones and aldehydes were selectively reduced to the corresponding saturated carbonyl compounds by Co₂(CO)₈-H₂O system. The current reducing system also offered a chemoselective reduction of less substituted unsaturated carbonyl groups.     

Synthesis of 2-(1-Hydroxyalkyl)acrylonitriles by the Cocatalysis of a Base and an Acid

Titled compounds are synthesized in good yields from acrylonitrile and saturated aliphatic aldehydes by the cocatalysis of tributylphophine and triethylaluminium.     

Stereoselective hydrosilylation of enals and enones catalysed by palladium nanoparticles

A highly versatile and efficient hydrosilylation method by palladium nanoparticle catalysis allows the direct and chemoselective synthesis of 1) enolsilanes of high isomeric purity, 2) saturated aldehydes or ketones, or 3) the corresponding saturated acetals from α,β-unsaturated aldehydes or ketones. The choice of the product is determined by simply switching the solvent from THF to mixtures of THF/water or THF/alcohol.     

Protonation of Homoenolate Equivalents Generated by N-Heterocyclic Carbenes

Homoenolate equivalents are generated by Lewis basic N-heterocyclic carbene catalysts and then protonated to generate efficiently saturated esters from unsaturated aldehydes. This reactivity is extended to the generation of β-acylvinyl anions from alkynyl aldehydes. The asymmetric protonation of a homoenolate equivalent generated from a β,β-disubstituted aldehyde can be accomplished with a chiral N-heterocyclic carbene.     

In-Solution Derivatization and Headspace Gas Chromatography–Mass Spectrometry for 56 Carbonyl Compounds in Tobacco Heating Products,Traditional Tobacco Products and Flavoring Capsules

Chromatographia - Optimal derivatization conditions were established for the simultaneous determination of 12 aliphatic saturated aldehydes, 8 aliphatic saturated ketones, 4 cyclic ketones, 3...     

A Novel Organocatalytic Asymmetric Transfer Hydrogenation of α,β‐Unsaturated Aldehydes

α,β‐Unsaturated aldehydes reacted with diimide (diazene) in the presence of optically active ammonium salt 1 as a catalyst to give the corresponding saturated aldehydes in excellent yields and up to 98 : 2 er. Attractive features of the asymmetric transfer hydrogenation are its high yields, and chemo‐, and enantioselectivities.     

Metal-assisted reactions—12 : Unusual selectivity in the reduction of ketones with zinc or cadmium bis-tetrahydroborate/dimethylformamide complex

Zinc bis-tetrahydroborate forms a solid complex with dimethylformamide (DMF) of composition, Zn(BH₄)₂ 1.5DMF. Unlike zinc bis-tetrahydroborate itself, the complex with DMF can be stored as a solid at room temperature. Ketones and aldehydes are reduced to the corresponding alcohols by the complex but the mechanism of reduction appears to be different from that using zinc bis-tetrahydroborate itself and from other tetrahydroborates in that only one hydride equivalent from each BH₄⁻ unit is utilized and not four. Further, although saturated aliphatic ketones are reduced rapidly to alcohols, aromatic ketones react much more slowly and ,β-unsaturated ketones react very slowly so that the complex appears to have selective reducing potential with regard to different classes of ketones. It is also apparent that the zinc bis-tetrahydroborate/DMF complex reduces sterically hindered saturated ketones much more slowly than it does unhindered ketones. An analogous cadmium bis-tetrahydroborate/DMF complex can be prepared in solution and reacts with ketones similarly to the zinc complex.     

Evaluation of solid-phase microextraction methods for determination of trace concentration aldehydes in aqueous solution

A method for trace analysis of a wide range of aldehydes (saturated/unsaturated aliphatic, aromatic aldehydes, including hydroxylated species, and dialdehydes) in an aqueous solution was optimized. An evaluation of three solid-phase microextraction (SPME) techniques (headspace, liquid-phase, and on-fiber derivatization) with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) aldehyde derivatization was performed focusing on the optimization of the main extraction parameters (temperature and time). The optimized method employed the liquid-phase SPME (D-L-SPME) of derivatized aldehydes at 80 degrees C for 30 min. Limits of detection (LODs) using this optimal method were in the range of 0.1-4.4 microg/L for the majority of aliphatic (saturated, unsaturated), aromatic aldehydes and dialdehydes. Formaldehyde LODs and those of some hydroxylated aromatic aldehydes were between 32 and 55 microg/L. Headspace SPME using an on-fiber derivatization generally showed a lower sensitivity and several compounds were not detected. Another technique, the optimized headspace SPME of aldehydes derivatized in aqueous solution, was not as sensitive as D-L-SPME for hydroxylated aromatic aldehydes. The developed method was used to analyze aqueous particulate matter extracts; this method achieved higher sensitivities than those obtained with US Environmental Protection Agency (EPA) Method 556.     

Selective Oxidation of Alcohols Using Benzyldimethyltelluronium Dichromate

Selective oxidation of benzylic, allylic, and saturated secondary alcohols to the corresponding aldehydes or ketones by benzyldimethyltelluronium dichromate is described.     

Palladium oxide nanoparticles supported on graphene oxide: A convenient heterogeneous catalyst for reduction of various carbonyl compounds using triethylsilane

Palladium oxide nanoparticles supported on graphene oxide ‐ triethylsilane was found to be an effective reductive system for a broad range of reduction processes, including the reduction of various carbonyl compounds such as aromatic aldehydes to their corresponding alcohols or methyl arene compounds, aromatic ketones to their respective alcohols or saturated compounds, aromatic acyl chlorides to their reduced compounds. The desired products were obtained in good to excellent yields under mild conditions. The heterogeneous environmentally friendly catalyst can be easily separated from the reaction mixture through a simple filtration, facilitating purification of the prepared compounds.     

Convenient Synthesis of Acyloins from Saturated Ethoxyethyl-Protected Cyanohydrins and α,β-Unsaturated Aldehydes

Functionalized acyloins have been synthesized via Umpolung from saturated ethoxyethyl-protected cyanohydrins and α,β-unsaturated aldehydes.     

Azo anions in synthesis : Use of trityl- and diphenyl-4-pyridylmethylhydrazones for reductive C-C bond formation

The lithium salts of trityl- and diphenyl-4-pyridylmethyl-hydrazones of both aldehydes and ketones react with electrophiles (alkyl halides, aldehydes, ketones, crotonates) at low temperature to form C-trapped azo compounds ; these Intermediates decompose homolytically with loss of nitrogen below room temperature and can be diverted in a synthetically useful way to alkanes, alkenes, alcohols or saturated esters.     

Knoevenagel kondensationen mit TiCl4/base-IV : Umsetzungen von aldehyden und ketonen mit phosphonoessigester und methylendiphosphonsäureestern

In the presence of titanium tetrachloride and an organic base in tetrahydrofurane, triethyl phosphonoacetic acid undergoes condensation with aliphatic and aromatic aldehydes and aromatic ketones to yield the corresponding triethyl alkylidene and arylidene phosphonoacetic acids respectively. Tetraalkyl methylenediphosphonates and aromatic or aliphatic α-branched aldehydes react under identical conditions in the same way. The largely unknown triethyl alkylidene and arylidene phosphonoacetic acids and the new tetraalkyl alkylidene and arylidene methanediphosphonic acids are easily hydrogenated either catalytically or by sodium borohydride in ethanol to give the corresponding saturated compounds in nearly quantitative yields.     

Chemoselective Carbonyl Reduction Mediated By Low-Valent Titanium

Utilizing the rate difference in alkoxy alkyl radical formation from aldehydes versus ketones with low-valent titanium, aldehydes are preferentially reduced with tributyltin hydride. The difference in reactivity allows aldehydes to be reduced in the presence of ketones without laborious protection-deprotection steps.     

Quantitative Analysis of aliphatic aldehydes by headspace SPME sampling and ion-trap GC-MS

Summary A fast and simple headspace SPME sampling method has been developed for quantification of volatile aliphatic aldehydes in sunflower oil. Analysis has been performed by gas chromatography, on a 30m×0.25 mm i.d. ×0.25 μm CP-Wax 52CB column, with mass spectrometric detection. Carryover from the SPME fiber could be eliminated by heating the fiber in the injection port between runs. Response factors of all the compounds were linear for concentrations up to 100 ng μL⁻¹. The slopes of the calibration curves decrease with the amount of saturation of the aldehydes. The average responses for unsaturated aldehydes were twice as high as those for the saturated variety. Responses for dienes were approximately one order of magnitude higher than for saturated aldehydes. Depletion of the analyte was examined by repeated extraction from the same vial. SPME was optimized—after 30 min extraction most components were found to have reached equilibration. The detection limit for the compounds studied varied between 0.1 and 1 ng μL⁻¹. Distribution constants were determined for ten different aldehydes and Henry's constants were calculated for unsaturated aldehydes. There was a definite relationship between the response factors and the amount of saturation of the aldehydes. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997     

Bridging the final gap in stereocontrolled wittig reactions: methoxymethoxy-armed allylic phosphorus ylides affording conjugated dienes with high cis selectivity

After treatment with an appropriate base (butyllithium or sodium amide), 2-alkenyltris(2-methoxymethoxyphenyl)phosphonium salts carrying an allyl, crotyl, or prenyl (3-methyl-2-butenyl) side chain condense with saturated or unsaturated aldehydes to give conjugated dienes with Z/E ratios ranging from 90:10 to > 99:1 and averaging 96:4. Owing to steric congestion, yields are only moderate (on average 41%; extremes 10-79%). The nonvolatile tris(2-methoxymethoxyphenyl)phosphine oxide by-product can be readily isolated and reduced to recover the phosphane starting material, or it may be hydrolyzed to the water-soluble tris(2-hydroxyphenyl)phosphine oxide.     

Application of Polymer Supported Oxidants for the Selective Oxidation of Alcohols

Allylic alcohols can be successfully oxidized into the corresponding α, β-unsaturated aldehydes by two new types polymer-supported oxidizing reagents which do not oxidize saturated alcohols under similar condition.