Acid-base properties of α-aminomethylphosphine oxides

Ionization constants of a series of aminomethylphosphine oxides and respective amino precursors, as well as their isostructural amino phosphonates in water-2-propanol or water medium were determined. The main regularities of the effect of the phosphoryl group on the protolytic equilibria involving mono- and bisphosphorylated amines and diamines were found. The environment effect on the ionization constants of hydrophilic aminophosphoryl compounds and amines was estimated quantitatively. The relationship between the dissociation constants of aminophosphoryl compounds and related constants of amino precursors in the framework of the principle of linearity of free energies was demonstrated.     

The effect of benzyl amine on the efficiency of the base-catalyzed transamination of α-keto esters

This paper describes the effect of benzyl amine on the base-catalyzed transamination of α-keto esters. Among various benzyl amines examined, o-HOC₆H₄CH₂NH₂ was found to be highly effective for the reaction, affording a wide variety of α-amino esters in good yields. The o-OH group of the benzyl amine facilitates the transamination process likely via H-bond. Moderate enantiomeric excess was obtained for α-amino ester when a quinine derived catalyst was used.     

Mechanism of dehydrogenation of cyclohexane on the crystalline α-oxide of chromium

Russian Chemical Bulletin - Dehydrogenation of cyclohexane on crystalline α-Cr2O3 proceeds according to a sextet-type mechanism. This conclusion agrees with the structural principles of...     

Novel approach to the synthesis of aliphatic and aromatic α-keto acids

A new practical and efficient synthesis of α-keto acids was accomplished starting from the synthon 1,4-diacetylpiperazine-2,5-dione. The synthesis encompasses both aromatic and aliphatic substrates proving to be versatile and innovative with excellent carbon economy and recycling of the glycine by-product.     

SPANamine derivatives in the catalytic asymmetric α-fluorination of β-keto esters

The use of C₂-symmetric enantiopure nitrogen ligands in the asymmetric catalytic α-fluorination of β-ketoesters is described. SPANamine 1 in the presence of nickel salts gives up to 63% ee in the fluorination of tert-butyl 2-oxocyclopentanecarboxylate with N-fluorosuccinimide (NFSI). The same enantioselectivity is obtained when SPANamine 1 is used as an organocatalyst, although the reaction is much slower.     

A Theoretical Studies on the Thermolysis Mechanism of α-Aminonitrile

Introduction α-Aminonitrile(or aminoacetonitrile) is a kind of reactive bioorganic molecules, and it may exist in insterstellar clouds. its importance lies in that a-aminonitrile may play a role in the generation of large carbon-nitrogen chain molecules. By means of flash vacuum thermolysis and gas-solid reaction (FVT-GSR) tech-nique, Guillemin, et al., studied the thermolysis of a-aminonitrile, they considered that the elimination of HCN (shown as following) is a key step in many reactions of α-     

Copper-bipyridine-catalyzed enantioselective α-amination of β-keto esters

The Cu(OTf)₂-bipyridine-catalyzed, enantioselective, direct α-amination of β-keto esters and β-diketones with diethyl azodicarboxylate (DEAD) has been studied. Exceptionally high enantioselectivities of up to 99% ee were found for 1-indanone-based β-keto esters in particular even for substrates and reagents carrying conventional ester groups such as methyl and ethyl.     

Asymmetric synthesis of β-amino alcohols by the transfer hydrogenation of α-keto imines

The asymmetric transfer hydrogenation of representative aryl and benzofuranyl 2-tert-butylaminoethanones with formic acid–triethylamine, catalyzed by RhCl[(R,R)-TsDPEN](C₅Me₅), produced the corresponding β-tert-butylamino alcohols in 97–99% ee. A short asymmetric synthesis of (R)-bufuralol, a potent β-adrenergic receptor antagonist, is described. This approach to β-amino alcohols from ketones circumvents the halogenation–reduction–amination sequence.     

MnIII-catalyzed phosphorylation of vinyl azides: The synthesis of β-keto phosphine oxides

Mn^III-catalyzed functionalization of vinyl azides via phosphorylation was developed to synthesize various β-keto phosphine oxides in high yields. The transformation is operated in mild conditions and tolerant of a range of functional groups. Control reaction indicates that the reaction mechanism might proceed via the generation of a phosphonated iminyl radical intermediate.     

Stabilizing influence of perfluoro-tert-butanol on α-keto radicals — the derivatives of perfluorinated α-diketones: quantum-chemical calculations of the formed complexes

Density functional theory calculations show that the heightened stability of α-keto radicals, the derivatives of perfluorinated α-diketones of general formula CF₃C(O)C(O)R^F (R^F = i-C₃F₇; t-C₄F₉), in perfluoro-tert-butanol can be caused by the H-bond-imposed formation of cation radicals of vicinal dienols.     

Polymerization Mechanism of α-Linear Olefin

The density functional theory on the level of B3LYP/6-31G was empolyed to study the chain growth mechanism in polymerization process of α-linear olefin in TiCl₃/AlEt₂Cl catalytic system to synthesize drag reduction agent. Full parameter optimization without symmetryrestrictions for reactants, products, the possible transition states, and intermediates wascalculated. Vibration frequency was analyzed for all of stagnation points on the potential energy surface at the same theoretical level. The internal reaction coordinate was calculated from the transition states to reactants and products respectively. The results showed as flloes:(i) Coordination compounds were formed on the optimum configuration of TiCl₃/AlEt₂Cl.(ii) The transition states were formed. The energy di?erence between transition states and the coordination compounds was 40.687 kJ/mol. (iii) Double bond opened and Ti-C(4) bond fractured, and the polymerization was completed. The calculation results also showedthat the chain growth mechanism did not essentially change with the increase of carbon atom number of α-linear olefin. From the relationship between polymerization activation energy and carbon atom number of the α-linear olefin, it can be seen that the α-linear olefin monomers with 6-10 carbon atoms had low activation energy and wide range. It was optimum to synthesize drag reduction agent by polymerization.     

Reaction of α-hydroxyiminoacetonitrile oxides with potassium thiocyanate

Potassium thiocyanate reacts with substituted -hydroxyiminoacetonitrile oxides in acetic acid to give, unexpectedly, 5-(carbamoyl)imino-²-1,4,2-oxathiazo-lines. The structure of 3-(1-adamantyl)-5-(carbamoyl)imino-²-1,4,2-oxathiazo-line has been confirmed by x-ray diffraction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 885–889, April, 1991.     

Preparation of α-methylene ketones by the palladium-catalyzed decarboxylation-deacetoxylation of allyl α-acetoxymethyl-β-keto carboxylates under mild conditions

α-Methylene ketones are prepared in high yields by the palladium-catalyzed decarboxylation-deacetoxylation of allyl α-acetoxymethyl-β-keto carboxylates. The reaction proceeds rapidly at room temperature under neutral conditions in acetonitrile.     

Unraveling the Mechanism of the IrIII-Catalyzed Regiospecific Synthesis of α-Chlorocarbonyl Compounds from Allylic Alcohols

We have used experimental studies and DFT calculations to investigate the Ir^III-catalyzed isomerization of allylic alcohols into carbonyl compounds, and the regiospecific isomerization–chlorination of allylic alcohols into α-chlorinated carbonyl compounds. The mechanism involves a hydride elimination followed by a migratory insertion step that may take place at Cβ but also at Cα with a small energy-barrier difference of 1.8 kcal mol⁻¹. After a protonation step, calculations show that the final tautomerization can take place both at the Ir center and outside the catalytic cycle. For the isomerization–chlorination reaction, calculations show that the chlorination step takes place outside the cycle with an energy barrier much lower than that for the tautomerization to yield the saturated ketone. All the energies in the proposed mechanism are plausible, and the cycle accounts for the experimental observations.     

Recent advances towards electrochemical transformations of α-keto acids

As a kind of environmentally benign reagents, α-keto acids have been extensively employed as key starting materials in organic synthesis. Organic electrosynthesis has the advantages of reducing byproduct generation, improving the cost-efficiency of synthetic processes, and accessing reactive intermediates under mild conditions. Inspired by the merits of organic electrosynthesis, α-keto acids have shown many synthetic applications in electrochemical acylation, cyclization, and reductive amination reactions with improved efficiencies and selectivities. This review covers the recent breakthroughs achieved in the electrochemical transformations of α-keto acids, aimed at highlighting these electrochemical reactions’ features and mechanistic rationalisations. Meanwhile, the practicalities and limitations of these transformations are also presented where possible.     

Novel fungi-catalyzed reduction of α-alkyl-β-keto esters

A screening of 15 fungi and yeast strains was carried out in fermentation processes to perform the diastereo- and enantioselective reduction of ethyl 2-methyl-3-oxobutanoate, to the corresponding (R¹,S¹)-3-hydroxy-2-methyl esters. Overall, biotransformations led to excellent conversions, as well as good to excellent diastereo- and enantioselectivities. A strain of Aureobasidium pullulans (CCM H1) was found to be the most efficient biocatalyst in terms of conversion (100%), syn:anti ratio (3:97), and enantiomeric excess (94% anti-(2S,3S) isomer). This biotransformation was successfully carried out on a preparative level as well. Other microorganisms, such as Fusarium graminearum (CCM HH 224), Aspergillus terreus (BFQU 121), Geotrichum candidum (CCM H38), Trichoderma koningii (ATCC 76666), and Aspergillus niger (CCM H21) also showed excellent diastereo- and enantioselectivities, combined with high conversions (>95% conversion, ?95% ee, and excellent syn:anti ratios). Many of the strains used in this work had scarcely been described as oxido-reducing agents, or had never been used with the substrates reported herein.     

Synthesis of α-Fluoro-β-keto Phosphonates from α-Fluoro Phosphonoacetatic Acid

A new synthesis of α-fluoro-β-keto phosphonates, via acylation reaction of α-fluoro phosphonoacetate dianion with carboxylic acid chlorides followed by decarboxylation, is described.