The Preparation of α-Phosphonovinylzirconocenes and their Application in the Stereospecific Synthesis of α-Halo-l-alkenylphosphonates

Hydrozirconation of 1-alkylnylphosphonates gives the organozirconium(Ⅳ) complexes 2 in syn-addition way.Complexs 2 was trapped with NCS,NBS or I2 to afford stereodifined α-halo-1-alkenylphosphonates in moderate to high yields.     

Preparation of conjugates of α-amylase with a protease inhibitor and their stability

A method for obtaining conjugates of -amylase with a trypsin inhibitor and separating them into fractions has been developed. Two fractions have been obtained—thermostable and thermolabile. The thermostable fraction retained about 80% of its amylase activity after incubation at 50°C for 2 h, with activation of the enzyme during the first 30 min. In the presence of trypsin the conjugated enzyme, retained 91% of its initial activity after incubation for 1 h, although the activity of the native enzyme fell to 35% under the same conditions.Mirzo Ulugbek [Ulugh-Beg] Tashkent State University. Translated from Khimiya Prirodnykh Soedimenii, No. 2, pp. 201–204, Marhc–April, 1998.     

Asymmetric synthesis of α-acetylenic epoxides

Chiral α-acetylenic oxiranes were easily synthesized from readily available propargylic esters by a four-step sequence involving the stereoselective reduction of α′-alkynyl β-keto sulfoxides with DIBAH (de 66–78%) and DIBAH/ZnBr₂ (de 78–88%), followed by further reduction of the resulting hydroxy sulfoxides into the corresponding sulfenyl derivatives and final epoxy ring closure via sulfonium salt.     

The Preparation of α-Phosphonovinylzirconocenes and their Application in the Stereospecific Synthesis of α-Halo-1 -alkenylphosphonates

Hydrozirconation of 1-alkylnylphosphonates gives the organozirconium(Ⅳ) complexes 2 in syn-addition way. Complexs 2 was trapped with NCS, NBS or I2 to afford stereodifined α-halo-1-alkenylphosphonates in moderate to high yields.     

Trifluoromethylated cyclopropanes and epoxides from CuI-mediated transformations of α-trifluoromethyl-diazophosphonate

An efficient method for the preparation of α-(trifluoromethyl)-cyclopropylphosphonates and α-(trifluoromethyl)-1,2-epoxyphosphonates has been developed. The method is based on metal-catalyzed reaction of diethyl 1-diazo-2,2,2-trifluoroethylphosphonate (1) with alkenes or carbonyl compounds, respectively. It established an essential advantage of CuI-catalysis over Rh₂(OAc)₄ in cyclopropanation reactions. An inexpensive copper iodide has also exhibited a good catalytic activity in the synthesis of epoxyphosphonates (3).     

AlEt3-promoted eliminative ring-opening of β-hydroxy epoxides: highly stereoselective synthesis of terminal α-hydroxy olefins

AlEt₃-promoted eliminative ring-opening of β-epoxy alcohols leading to α-hydroxy olefins is reported. This eliminative ring-opening reaction is shown to be highly stereoselective, thus providing an alternative asymmetric synthesis for α-hydroxy olefins.     

Addition of carbon dioxide to epoxides catalyzed by the mixtures of α-amino acids and iodine

Russian Chemical Bulletin - We found a group of available and efficient catalysts for the addition reaction of CO2 to epoxides, which was formed by simple mixing of molecular iodine with...     

The Preparation and Properties of Some α-Acyloxy- and α-Carbamoyloxy-Phosphonothionates

New f -acyloxy and f -carbamoyloxy derivatives of dimethyl 2,2,2-trichloroethyl-phosphonothionate have been prepared, characterized, and screened for activity against free-living soil nematodes. Several of the more easily hydrolysable esters, and also the N -methylcarbamoyl derivative, were as active as the parent pesticide, dimethyl f -hydroxy-2,2,2-trichloroethylphosphonothionate, after an induction period during which the active species is assumed to be released in vivo . It is concluded that the 2,2,2-trichloroethyl group is essential for activity in compounds of these types and that the presence of the N -methylcarbamoyl group does not in itself confer activity.     

Preparation of n-oxides of α− and α′-A minonicotines

Summary All possible N-oxides of -benzamidonicotine were prepared and were hydrolyzed with hydrochloric acid to N-oxides of the corresponding -aminonicotines.     

The thermolysis of α-pinene and verbenone epoxides in supercritical solvents

Thermal transformations of α-pinene and verbenone epoxides were studied in supercritical solvents with complex compositions, including CO₂, lower alcohols (ethanol and isopropanol), and water, over the temperature and pressure ranges 387–575 K and 135–215 atm. The main product from α-pinene epoxide in a supercritical solvent containing water was campholenic aldehyde and pinocamphone; the total content of these products in the reaction mixture was 80%. Suggestions concerning the mechanism of the thermal isomerization of α-pinene epoxide depending on the acidity of supercritical solvents were made. The direction of verbenone epoxide transformations was independent of the presence of water in the mixture. The main identified products were ketoalcohols with para-menthane and camphane frameworks.     

Preparation of α-fluoroaldehydes and α-fluoroketones using dilute fluorine

Fluorination of silyl enol ethers with 5% F₂ in N₂ at −78°C in Freon 11 results in the formation of α-fluoroketones and α-fluoroaldehydes.     

The Preparation of α-Fluorosulfoxides and Vinyl Fluorides

Treatment of thioacetals with HgF2 in anhydrous acetonitrile, followed by oxidation with MCPBA results in the formation of α-fluorosulfoxides, which can be pyrolyzed to give vinyl fluorides.     

Preparation of 1-aryl-2,2-difluoro enol esters via dehydrosulfonylation of α-(phenylsulfonyl)difluoromethylated benzoates

1-Aryl-2,2-difluoro enol benzoates 4 has been prepared from α-(phenylsulfonyl)-difluoromethylated benzoates 3, which can be readily obtained from the reactions between simple aldehydes and PhSO₂CF₂H (or TMSCF₂SO₂Ph). 2,2-Difluoro enol esters 4 are relatively more stable compounds than 2,2-difluoro enol sily ethers, and they promise to act as interesting fluorinated building blocks for further elaborations.     

Asymmetric oxidation of enol phosphates to α-hydroxy ketones using Sharpless reagents and a fructose derived dioxirane

The asymmetric oxidation of a variety of differently substituted, acyclic and cyclic enol phosphates using the Sharpless AD-reagents AD-mix-α and AD-mix-β, and a fructose derived chiral ketone as a catalyst, afforded the corresponding α-hydroxy ketones in high enantioselectivity and good yield. The influence of steric and electronic factors of the substrates on the facial stereoselectivity in the reported oxidations was studied.     

Preparation of proximal β-hydroxy silyl enol ethers from α,β-epoxyketones using silyllithium reagents

A new method for the stereoselective preparation of proximal β-hydroxy silyl enol ethers from α,β-epoxyketones using silyllithium reagents has been developed. The reaction is believed to proceed via Brook rearrangement assisted by opening of the adjacent epoxide. A number of α,β-epoxyketones were reacted with methyldiphenylsilyllithium to form the corresponding proximal β-hydroxy silyl enol ethers in good to excellent yield and excellent stereoselectivity.     

Synthesis of α-N-Ethylamino Acids and their Derivatives

 A new synthesis of α-N-ethylamino acids starting from α-amino acids using hexafluoroacetone as protecting and activating agent is described. The hexafluoroacetone-protected N-ethylamino acid derivatives obtained are activated lactons. Therefore, they can be directly transformed without the need of an additional activation step with various nucleophiles into the corresponding carboxylic acid derivatives.