Biomimetic reductive amination under the continuous-flow reaction conditions

This study present a full account of continuous-flow reaction conditions for biomimetic reductive amination of fluorinated carbonyl compounds to corresponding amines and amino acids of biomedical importance. We demonstrate that simple silica-adsorbed DBU can be used as efficient catalysts for on-column 1,3-proton shift reaction, a key transformation in the biomimetic reductive amination process. This new on-column process features operationally convenient conditions, higher chemical yields, enantioselectivity and purity of the corresponding products as compared with traditional in-flask reactions. Moreover the removal of base-catalyst, the most delicate problem of the in-flask reactions, is not an issue in the on-column process, as the silica-adsorbed DBU or polymer-bound guanidine remains on the column and can be reused. This feature renders the overall process substantially more economical and synthetically efficient, in particular, for large-scale synthesis of the corresponding fluorinated amines and amino acids target.     

Reaction of 2,6-dibenzylidenecyclohexanone with phosphorus pentachloride: Triple functionalization of the isosemiquinoid system

The reaction of 2,6-dibenzylidenecyclohexanone with PCl₅ occursvia the sequential stages of desoxychlorination and substitutional phosphorylation to form (after oxidation, methoxylation, and hydrolysis on the surface of the chromatographic SiO₂ adsorbent) organophosphorus products of the 1-(a-chloro-, a-hydroxy-, or -alkoxy)benzyl-2-chloro-3-(-(dimethylphosphoryl)benzylidene)cyclobex-1-ene series.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 441–443, February, 1996.     

Platinum-catalyzed reductive coupling of activated alkenes under hydrogenation conditions

The Pt complex generated from PtCl₂, PR₃, and SnCl₂ catalyzes the reductive coupling of activated alkenes under environmentally benign hydrogenation conditions. Various bis-enones participated in the intramolecular cyclization, forming the desired cyclization products in moderate to good yield. Intermolecular reductive coupling of the enone and the aldehyde provided the coupling product in good yield. This methodology illustrates the first use of platinum complexes in hydrogen-mediated couplings of activated alkenes.     

Oxidative and reductive carbodiazenylation of nonactivated olefins

Procedures for the carbodiazenylation of nonactivated olefins with a wide range of aryldiazonium salts have been developed. The azo compounds obtained can serve as valuable precursors for beta-arylamines (carboamination products), beta-amino acids, ketones, and various heterocyclic structures.     

Oxidative degradation of porphyrins and metalloporphyrins under polythermal conditions

Influence of structure on the thermal properties of a large group of natural and synthetic porphyrins (H₂P) and metalloporphyrins (MP) was analyzed on the ground of thermogravimetric studies. The initial stage of thermal degradation of “classical” porphyrin containing a flat or pseudo-planar macrocycle is a result of oxidative degradation of the macrocyclic structure with the formation of linear tetrapyrrols. The negative effect on the thermal stability of porphyrins exerts the violation of the planar structure of the macrocycle, and the presence of bulky alkyl and polar pseudoalkyl substituents. In many cases, the general trend in the decrease in the stability of metalloporphyrins (MP) in comparison with the corresponding H₂P is a consequence of intramolecular metal ↔ ligand redox processes.     

A highly active catalyst for the reductive cyclization of ortho-nitrostyrenes under mild conditions

A mild and efficient method for the palladium-catalyzed reductive cyclization of ortho-nitrostyrenes to afford indoles is reported. Treatment of ortho-nitrostyrenes with 0.1 mol% palladium (II) trifluoroacetate [Pd(TFA)₂] and 0.7 mol% 3,4,7,8-tetramethyl-1,10-phenanthroline (tm-phen) in DMF at 15 psig CO and 80 °C afforded indoles in good to excellent yields. When the reaction was conducted in toluene, the corresponding N-hydroxyindole was isolated. A mechanism that accounts for the formation of N-hydroxyindole is proposed.     

Oxidative ammolysis of wood under the conditions of cavitation treatment

Effect of the composition of the lignocarbohydrate vegetable raw material, treatment duration, amount of ammonium persulfate, and concentration of free ammonia on the yield of the target product and on its content of nitrogen, carboxy groups, and lignin upon oxidative ammonolysis of vegetable waste with ammonium persulfate in aqueous ammonia under the conditions of cavitation treatment was examined. The agrochemical tests of the products as nitrogen-containing fertilizers were performed.     

One-pot reductive amination of aldehydes and ketones with α-picoline-borane in methanol, in water, and in neat conditions

A one-pot reductive amination of aldehydes and ketones with amines using α-picoline-borane as a reducing agent is described. The reaction has been carried out in MeOH, in H₂O, and in neat conditions in the presence of small amounts of AcOH. This is a highly efficient and mild procedure that is applicable for a wide variety of substrates. In particular, this is the first successful demonstration that this type of reaction can be carried out in water and in neat conditions.     

Radical cyclizations to quinolone and isoquinolone systems under oxidative and reductive conditions

Radical cyclizations to quinolone and isoquinolone systems under Fenton-type and n-Bu₃SnH-mediated conditions are described. For N-iodoalkylquinolones, ca. 3:1 mixtures of oxidative cyclization products at C-2, and unexpectedly at C-8, were obtained under both conditions. Five- or six-membered oxidative cyclization products were obtained from N-iodoalkylisoquinolones under Fenton-type conditions, whereas n-Bu₃SnH-mediated reactions gave products of reductive cyclization in the five, six, and seven-membered series.     

A one-pot process for the enantioselective synthesis of amines via reductive amination under transfer hydrogenation conditions

[reaction: see text]. Cyclic amines may be prepared via a sequence of deprotection followed by intramolecular reductive amination of t-Boc-protected amino ketones under asymmetric transfer hydrogenation conditions. In cases where the corresponding imine reaction proceeds with high enantioselectivity, this is reflected in the one-step process.     

Pulse radiolysis of tetrazolium violet in aqueous and aqueous-alcoholic solutions under oxidative and reductive conditions

The radiolytic reduction of colourless tetrazolium salts to coloured formazans in liquid and solid state is suggested for dosimetry purposes. In order to clarify the reaction mechanism, a pulse radiolysis study was conducted in aqueous and aqueous-alcoholic solutions under oxidative and reductive conditions. Under reducing conditions, fast formation of the electron adduct tetrazolinyl radical was observed: coloured formazan final product formed during the decay of electron adduct. Both the decay of the tetrazolinyl radical and the formation of the formazan were found to be second order. The spectra of the formazan were similar in neutral and alkaline solutions, but with higher absorbance in the latter solutions due to the higher molar absorption coefficient. Under oxidative conditions formazan did not form; hydroxylated products through OH-adducts were observed in the pH range studied.     

Decatungstate photocatalyzed oxygenation of methanol in acetonitrile under photostationary state conditions

Complementary techniques including laser flash photolysis have been used to investigate the mechanism of decatungstate photocatalyzed oxygenation of methanol in acetonitrile. A particular attention has been directed to determine the most important chemical and photophysical kinetic parameters of this peculiar reaction. Under continuous photolysis, kinetics of both oxygen consumption and hydrogen peroxide formation has been followed in a closed system. The reaction was stopped when a conversion of less than 10% in oxygen-saturated solutions was reached. Our work enlightens the following findings: (i) as expected on the basis of a hydrogen-atom-abstraction mechanism and relative CH bond dissociation energy, the reaction constant rate of reactive species wO with methanol is the weakest of all alcohols already studied, (ii) the methanol decatungstate photocatalyzed oxygenation in acetonitrile satisfies the photostationary state conditions only up to [CH₃OH] ∼ 2.5 M, (iii) the role of peroxyl radical is crucial since it not only leads to the resulting products, but it also oxidizes the reduced form of decatungstate H⁺W₁₀O₃₂⁵⁻ to regenerate the catalyst, thus closing the catalytic cycle, and (iv) progressive establishment of anaerobic conditions results in both ending of the substrate conversion and the decay of hydrogen peroxide. Hence, these findings offer new insights into the nature of the rate-determining step in the photocatalytic cycle.     

Hydrogen generation from methanol reforming under unprecedented mild conditions

A homogeneous catalyst [Cp^*Rh(NH₃)(H₂O)₂]³⁺ has been found for the clean conversion of methanol and water to hydrogen and carbon dioxide.The simple and easily available reaction steps can circumvent the formation of CO,therefore,making it possible to avoid inactivating catalysts and contaminating the hydrogen fuel.Different from conventional reforming method for hydrogen production,no additional alkaline or organic substances are required in this method.Valuable hydrogen can be obtained under ambient pressure at 70℃,corresponding TOF is 83.2 h^-1.This is an unprecedented success in reforming methanol to hydrogen.Effects of reaction conditions,such as reaction temperature,initial methanol concentration and the initial pH value of buffer solution on the hydrogen evolution are all systematically investigated.In a certain range,higher reaction temperature will accelerate reaction rate.The slightly acidic condition is conducive to rapid hydrogen production.These findings are of great significance to the present establishment of the carbon-neutral methanol economy.     

Substitution of poly(chlorotrifluoroethylene) with sulfur dioxide under reductive conditions

Treatment of Poly(chlorotrifluoroethylene) (in the forms of Kel-F 6061 and Neoflon M400H) with Zn/SO₂ in DMF results in substitution of the chloride ligand with the sulfinic acid moiety. Subsequent oxidation affords the sulfonic acid. The materials are characterized by elemental analysis, titration, scanning electron microscopy, and FT-IR. ATR-IR studies indicate that functionalization is probably not a surface-selective phenomenon. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:265–269, 1998