Free radical chlorination of methyl derivatives of pyridine,pyrazine, and thiazole by N-chlorosuccinimide

When methylazines (2-, 3-, and 4-methylpyridines, methylpyrazine) are treated with N-chlorosuccinimide they undergo successive chlorination of the methyl group to give 2-chloromethylpyridine, 2-dichloromethylpyridine, and dichloromethylpyrazine in preparative yields. 3-Dichloromethylpyridine was synthesized from pyridine-3-aldehyde and PC1₅. The primary chlorination products of 4-methylthiazole are 4-methyl-5-chlorothiazole and 5-chloro-4-chloromethylthiazole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 543–546, April, 1989.     

Primary methods for the measurement of electrolytic conductivity

This paper surveys the state of the art for primary methods for the evaluation of electrolytic conductivity in aqueous solutions as they are currently carried out in several national metrological institutes (NMIs). The theoretical and practical basic knowledge of this measurement is described. Analysis of and comments on the different approaches are offered to give emphasis to technical difficulties and possible solutions. Further development is foreseeable, ensuring a common effort for the sharing of expertise that has been undertaken at the NMIs. In particular, improvements are expected towards traceable measurements of solutions with conductivity values lower than those actually standardized, down to the level of ultrapure water.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

Phase transfer catalytic synthesis of silyl derivatives of heterocyclic thiols

Reactions of heteroaromatic thiols with trialkylsilylakyl iodides in the two-phase catalytic system (solid K₂CO₃/18-crown-6/toluene) at 111°C selectively lead to formation of the corresponding (trialkylsilylalkyl)thiohetarenes. 6-Mercaptopurine in the presence of two equivalents of alkylating agent yields S,N-dialkylated derivatives.Dedicated to the 100th anniversary of the birth of Academician A. N. Nesmeyanov.Latvian Institute of Organic Synthesis, Riga LV-1006, Latvia Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1197–1202, September, 1999.     

Catalytic enantioselective hydroboration of cyclopropenes

2,2-Disubstituted cyclopropyl boronates have been synthesized with high degrees of diastereo- and enantioselectivity via the rhodium-catalyzed asymmetric hydroboration of 3,3-disubstituted cyclopropenes. A strong directing effect of ester and alkoxymethyl substituents has been demonstrated. The directing effect was found to be necessary in achieving high degrees of enantiomeric induction. Selected cyclopropylboronic derivatives were successfully employed in the Suzuki cross-coupling reaction to produce the corresponding optically active aryl- and vinylcyclopropanes in good yields.     

Vapor phase oxidation of methylpyridines on zeolite catalysts

It has been established that zeolites containing Pd and Cu ions catalyze the vapor phase oxidation of methylpyridines. In oxidation of 2-methylpyridine on PdCuNa-mordenite at 375 °C the yield of 2-pyridinecarbaldehyde is 40 % of its theoretical values.

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, , Pd Cu, . 2- PdCuNa- 2- 375°C 40% .

     

Prototropic Rearrangement of 2-Propynyl(methyl)amino, 2-Propynyloxy,and 2-Propynylsulfanyl Derivatives of Hetarenes under Conditions of Phase-Transfer Catalysis: Mechanism and Limitations

2-Propynyl derivatives of N-methylaniline, phenol, benzenethiol, 2-pyridinethiol, 2-pyrimidinethiol, and 1,3-benzoxazole-2-thiol were synthesized. Under conditions of phase-transfer catalysis, phenyl 2-propynyl sulfide is converted into allenyl phenyl sulfide and phenyl 1-propynyl sulfide. The rearrangement mechanism was studied by the AM1 quantum-chemical method.     

Palladium-catalyzed highly chemo- and regioselective formal [2+2+2] sequential cycloaddition of alkynes: a renaissance of the well known trimerization reaction?

A new concept of highly chemo- and regioselective formation of the benzene ring by a palladium-catalyzed formal [2 + 2 + 2] sequential intermolecular trimerization of alkynes is proposed. Homodimerization of terminal alkynes and subsequent [4 + 2] benzannulation with diynes gives tetrasubstituted benzenes in moderate to good yields. The introduction of two different alkynes (terminal and internal) in the first step of the sequence allows for construction of pentasubstituted benzenes from three different acyclic acetylenic units. In all cases the tetra- and pentasubstituted benzenes are formed as a single reaction product without being accompanied by any of regio- or chemoisomers. A significant acceleration of the sequential trimerization reaction in the presence of Lewis acid/phosphine combined system was observed. Mechanistic studies reveal that the Lewis acid assisted isomerization of the E-enyne formed in the first step of the sequence to the more reactive Z-isomer is responsible for the observed acceleration effect. The proposed methodology provides a conceptually new and synthetically useful route to multifunctional aromatic compounds.     

On solving the potential equation

We study radial solutions to the generalized Swift-Hohenberg equation on the plane with an additional quadratic term. We find stationary localized radial solutions that decay at infinity and solutions that tend to constants as the radius increases unboundedly (“droplets”). We formulate existence theorems for droplets and sketch the proofs employing the properties of the limit system as r → ∞. This system is a Hamiltonian system corresponding to a spatially one-dimensional stationary Swift-Hohenberg equation. We analyze the properties of this system and also discuss concentric-wave-type solutions. All the results are obtained by combining the methods of the theory of dynamical systems, in particular, the theory of homo-and heteroclinic orbits, and numerical simulation.     

1,2-Halogen migration in haloallenyl ketones: regiodivergent synthesis of halofurans

Selective 1,2-iodine, bromine, and chlorine migration in haloallenyl ketones in the presence of Au catalyst has been demonstrated. It was found that, depending on the nature of the Au catalyst used, either selective bromine migration or hydrogen shift occurs, leading to the formation of 3- or 2-bromofurans, respectively. Halirenium intermediate was proposed for the unusual 1,2-halogen migration. This cascade transformation allows for mild and efficient synthesis of various types of 3-halofurans.