Selective synthesis of 1-vinylpyrroles directly from ketones and acetylene: Modification of trofimov reaction

Consecutive treatment of ketones with a system NH₂OH·HCl-NaHCO₃-DMSO and acetylene excess in the presence of KOH (100–120°C, initial acetylene pressure 12–15 at) led to a selective formation of 2-and 2,3-substituted 1-vinylpyrroles in 51–79% yields. Ketones of aliphatic, cycloaliphatic, aromatic, heteroaromatic, and tetrahydronaphthalene series were involved into the reaction.     

Free-radical addition of alkanethiols to 1-vinylpyrroles

In the presence of 2,2-azobisisobutyronitrile or in the absence of an initiator alkanethiols add to 1-vinylpyrroles exclusively counter to Markovnikov's rule to give 1-(2-alkylthioethyl)pyrroles (in yields up to 94%).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1636–1639, December, 1977.     

Conformational study of 2-arylazo-1-vinylpyrroles

Conformational study of 2-phenylazo-1-vinylpyrrole and 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole was performed on the basis of the experimental measurements and high-level ab initio calculations of their 13C--13C and 13C--1H spin-spin coupling constants, showing marked stereochemical behaviour upon the internal rotation of the vinyl group and the pyrrolyl moiety. In liquid phase, both compounds were found to adopt predominant s-trans-s-trans conformation with the noticeable population (ca. 30%) of the higher-energy s-cis-s-trans conformation in the latter compound. As follows from the X-ray data, 2-phenylazo-1-vinylpyrrole crystallizes in s-trans-s-trans conformation while the crystalline molecular structure of 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole is s-cis-s-trans.     

NMR spectra and structures of protonated 1-vinylpyrroles

Stable 1-vinylpyrrolium fluorosulfonates were prepared by the reaction of 1-vinylpyrroles with excess HSO₃F at –50°C in CD₂Cl₂ and their ¹H and ¹³C NMR spectra were obtained. Despite its overall positive charge, the pyrrole ring remains an electron donor relative to the vinyl group. Delocalization of the positive charge onto substituents decreases in the order 2-heteroaryl > 2-aryl > 2-alkyl.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 48–57, January, 1993.     

Selective catalytic hydrogenation of acetylenes

The products of the stepwise catalytic hydrogenation of undeca-1,7-diyne (I) have been examined and the sequence of the reduction established. The ethynyl group may be protected during catalytic hydrogenation by conversion into the corresponding 1-bromoacetylene.

Certain palladium catalysts have been shown to produce substantial amounts of trans-ethylene in the catalytic partial reduction of several acetylenic hydrocarbons. Catalytic stereomutation of cis- to trans-ethylene has been observed, the extent of which depends on the relative proportions of catalyst and unsaturated hydrocarbon.     

Selective hydrogenation with the use of nanocatalysts

Russian Journal of Applied Chemistry - Process of single-stage hydrogenation of phenol to cyclohexanone with industrial (domestic and imported) palladium catalysts, and also with nanocatalysts...     

Selective hydrogenation of carbonyl group ofα,β-unsatueated aldehydes in the presence of iridium catalyst

Conclusions ,-Unsaturated aldehydes (furylacrolein, crotonaldehyde, cinnamaldehyde, citral) are quantitatively hydrogenated to the corresponding unsaturated alcohols in the presence of iridium catalyst. The hydrogenation of acrolein gives a mixture of products, containing mainly allyl alcohol.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1993–1998, September 1972.     

2-Arylazo-1-vinylpyrroles: Free-radical polymerization and copolymerization

2-Arylazo-1-vinylpyrroles (a new group of azo dyes of the pyrrole series) are polymerized under heating (80°C) without initiators and in the presence of AIBN to form intensely colored paramagnetic and conducting polymers with a yield of 92%. By the example of the thermal copolymerization with 1-vinylpyrrolidone, it has been shown that 2-arylazo-1-vinylpyrroles may simultaneously play the roles of initiators and comonomers.     

Selective protecting group manipulations on the 1-deoxynojirimycin scaffold

Iminosugars are inhibitors of glycoprocessing and are of interest as scaffolds for medicinal chemistry, as their successful application as peptide mimetics has shown. The synthesis of novel peptidomimetics based on 1-deoxynojirimycin (DNJ) requires practical strategies that allow introduction of amino acid side chains or pharmacophore groups at each of its hydroxyl groups or to the nitrogen atom. This paper describes one approach towards achieving selective protection and deprotection at the hydroxyl and amino groups of DNJ and a novel synthesis of DNJ from l-sorbose is included.     

Direct13C-1H coupling constants in the vinyl group of 1-vinylpyrazoles

Conclusions The¹³C-¹H direct coupling constants in the vinyl group of 1-vinylpyrazoles are stereo-specific and vary with change in the conformer ratio.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 202–204, January, 1987.     

Selective hydrogenation of nitro derivatives of hydroquinolines

By catalytic hydrogenation of p-nitrophenylhydroquinolines with 5-oxo- and 5-oxime functional groups in the presence of heterogeneous palladium complex catalysts, we have obtained the corresponding amino derivatives.Scientific-Research Institute of Chemistry at Saratov State University, Saratov 410026. Translated from Khimiya Geterotsildicheskikh Soedinenii, No. 8, pp. 1138–1140, August, 1995. Original article submitted June 8, 1995.     

Selective iron-catalyzed transfer hydrogenation of terminal alkynes

A novel iron-catalyzed transfer hydrogenation of alkynes to the corresponding alkenes applying formic acid as a hydrogen donor is reported. An in situ combination of Fe(BF(4))(2)·6H(2)O and tetraphos allows for highly selective hydrogenation of a broad range of aromatic and aliphatic alkynes tolerating different functional groups.     

Selective hydrogenation of nitrobenzene in aprotic media

The kinetics of hydrogenation of nitrobenzene in aprotic media was studied, and a scheme of the mechanism and a kinetic equation, corresponding to it, for the initial reaction rate are proposed. High selectivity with respect to N-phenylhydroxylamine is apparently due to the aprotic nature and donor properties of the solvent and also to the functioning of the catalyst as a unique hydrogen electrode.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 45–48, January, 1991.The author thanks V. V. Strelets for useful discussion.     

Selective hydrogenation of styrene/1-octene mixtures over a monolithic Pd catalyst

Mixtures of styrene and 1-octene in toluene were hydrogenated over a monolithic Pd catalyst in the three-phase regime. Styrene was preferably hydrogenated to ethylbenzene, while a major part of the initial quantity of 1-octene was isomerized to internal olefins. Formation of alkylcyclohexanes was negligible. Observed rates of styrene hydrogenation were high compared to the values listed in literature.     

Catalytic enantioselective hydrogenation of vinyl bis(boronates)

Catalytic enantioselective hydrogenation of prochiral vinylmetallic reagents can provide an attractive alternative to hydrometalation and bismetalation of alkenes. In this contribution, the first highly enantioselective hydrogenation of vinyl boronic esters is described. The chiral reduction products are versatile intermediates for chemical synthesis.     

Analysis of influence of the 5-methyl group on internal rotation of the vinyl group in 1-vinylpyrazoles,by the AM-1 method

According to results obtained in quantum-chemical calculations by the AM-1 method, 1-vinyl- and 1-vinyl-5-methylpyrazole may exist in the s-cis(N₂) and s-trans(N₂) conformations. The introduction of the CH₃ group into position 5 of the pyrazole ring gives a substantial increase in population of the s-cis form, and also increases the interval of torsional vibrations of the vinyl group around the equilibrium position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2077–2079, September, 1991.     

2-Arylazo-1-vinylpyrroles: oligomerization in the presence of protic and aprotic acids

2-Arylazo-1-vinylpyrroles react with protic (CF₃COOH, HCl) and aprotic (BF₃) acids forming deeply colored oligomeric products consisting of soluble (in benzene, chloroform) and insoluble fractions with yields amounting to 73 %. According to the data from ¹H NMR and IR spectroscopy oligomerization takes place mainly at the 1-vinyl group with partial involvement of the pyrrole ring. The process is accompanied by capture of the catalyzing acids by the azo group, leading to strong polarization of the elementary unit with transfer of positive charge to the pyrrole ring, which thus becomes capable of further transformations with cross-linking of oligomeric chains. The obtained oligomers possess electric conductivity of 10⁻¹³-10⁻⁹ S/cm, which is increased to 4.8∙10⁻⁶ S/cm when the products are iodinated with iodine vapor.     

Study of internal rotation of the vinyl group in 1-, vinylpyridones by the AM-1 method

By the AM-1 method in the semirigid model approximation, the potential energy of internal rotation of the vinyl group has been calculated for 1-vinyl-2-pyridone, 1-vinyl-6-methyl-2-pyridone, and 1-vinyl-4-pyridone. The potential energy of internal rotation in the first and third of these molecules has two minima corresponding to torsion angles around the N-C bond approximately 0 and 180°, separated by barriers to internal rotation 3.99 and 2.94 kcal/mole, respectively. For the 1-vinyl-2-pyridone, the energy minimum at =180°, the s-cis(O) conformation, is 1.83 kcal/mole above the first minimum. For the 1-vinyl-6-methyl-2-pyridone, the torsion angles 0 and 180° correspond to energy maxima; the energy minima occur at 35° and 140°. In the harmonic oscillator approximation, the intervals of torsional vibrations of the vinyl group in these comopunds have been estimated. Data from the AM-1 calculation are in qualitative agreement with the available¹H and¹³C NMR data on the structure of 1-vinyl-2-pyridone, 1-vinyl-5-methyl-2-pyridone, and 1-vinyl-4-pyridone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1367–1372, June, 1991.     

Selective hydrogenation of phenol in supercritical carbon dioxide

Liquid phase hydrogenation of phenol over Pt/C catalysts was investigated under conventional conditions and supercritical carbon dioxide (scCO2). The equivalent ration of hydrogen to phenol shows a significant effect on the product selectivity. Hydrogenation of phenol in different solvents was also studied, the experimental results show that polarity of solvents influences the yield of cyclohexanone remarkably, scCO2 has the highest one. Catalytic hydrogenation of phenol in scCO2 or sub-scCO2 was emphatically researched. The result is that near the critical point of CO2 phenol has higher reaction activity than that of normal organic solvents, cyclohexanone has 47% in yield and 87% in selectivity.