Acyl migration from N to C in aziridine-2-carboxylic esters

Acyl group migration from N to C in aziridine-2-carboxylates takes place in deprotonation reactions and, as a result, aziridine-2,2-dicarboxylates are formed. Mechanistic studies proved that the observed migration is an intramolecular reaction.     

A parametrization of matrix conjugacy orbit sets as unions of affine planes

The problem of finding a canonical form of complex matrices up to conjugacy with the set of canonical matrices being a union of affine planes in the matrix space is considered. A solution of the problem is given.     

Facile synthesis of coumarin bioisosteres—1,2-benzoxathiine 2,2-dioxides

A simple and reproducible procedure for the synthesis of bioisosteres of coumarin—1,2-benzoxathiine 2,2-dioxide is presented. The developed method is based on the intramolecular aldol cyclization of derivatives of mesylsalicyl aldehydes in the presence of strong organic bases, where best results were obtained with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). It has been shown that depending on the nature of the substituent in the aromatic ring, intermediate aldol adducts (3,4-dihydro-1,2-benzoxathiin-4-ol 2,2-dioxides) in different ratios with title compound are formed. Dehydration of the intermediate aldols with POCl₃ led to full conversion into 1,2-benzoxathiine 2,2-dioxide derivatives. The scaffold of 1,2-benzoxathiine 2,2-dioxide is unequivocally proven by a single-crystal X-ray structure.     

Effect of light polarization on holographic recording in glassy azocompounds and chalcogenides

Light polarization effects on a holographic grating recording in a glassy chalcogenide a-As₄₀S₁₅Se₄₅ film has been experimentally studied and compared with previously studied glassy molecular azobenzene film 8a at 633, using s − s,p − p, CE-1 and CE-2 circular-elliptic recording-beam polarizations (differing by light electric field rotation directions). The azocompound exhibited much higher self-diffraction efficiency (SDE) and diffraction efficiency whereas chalcogenide was more sensitive. Their recording efficiency polarization dependences also were different. SDE up to 45% was achieved in 8a with p − p and up to 2.6% in a-As₄₀S₁₅Se₄₅ with CE-2 polarized recording beams. The polarization changes in the diffraction process were studied as well in these and other materials (11, 16, 19 and a-As₂S₃ film, LiTaO₃:Fe crystal). It was found that light polarization changes in the process of diffraction from gratings recorded vectorially by s−p polarizations depended on chemical composition, wavelength, and exposure time. Vector gratings with SDE up to 25% were recorded in 8a, rotating a linear polarization by 90°. No light polarization changes were found in azobenzene 19 and chalcogenide films and in LiTaO₃:Fe crystal, thus showing a vector recording of scalar holograms. The recording mechanisms in azocompounds and chalcogenides are discussed and compared.     

Imidazolium and pyridinium salts – solvents influencing the rate and direction of the Fries,Beckmann, and Claisen rearrangements

The Fries, Beckmann, and Claisen rearrangements have been investigated in ionic liquid media. The effect of the structural elements of the latter on the direction of these rearrangements and the product yields has been studied.     

The effect of substrate roughness on the static friction of CuO nanowires

The dependence of static friction on surface roughness was measured for copper oxide nanowires on silicon wafers coated with amorphous silicon. The surface roughness of the substrate was varied to different extent by the chemical etching of the substrates. For friction measurements, the nanowires (NWs) were pushed by an atomic-force microscope (AFM) tip at one end of the NW until complete displacement of the NW was achieved. The elastic bending profile of a NW during this manipulation process was used to calculate the ultimate static friction force. A strong dependence of static friction on surface roughness was demonstrated. The real contact area and interfacial shear strength were estimated using a multiple elastic asperity model, which is based on the Derjaguin–Muller–Toporov (DMT) contact mechanics. The model included vertical elastic flexure of NW rested on high asperities due to van der Waals force.     

Alkylation of the ambident indole ion in ionic liquids

Alkylation of the ambident indole anion in ionic liquids has been investigated. The reaction rate is greater in ionic liquids than in organic solvents. The polarity of certain ionic liquids has been determined to be located between methanol and acetonitrile. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 676–690. May, 2008.     

Benzo[b]thiophen-3(2H)-one 1,1-dioxide—a versatile reagent in the synthesis of spiroheterocycles

New applications of benzo[b]thiophen-3(2H)-one 1,1-dioxide have been investigated. The synthesis of a new heterocyclic system 3H,2′H-spiro[benzo[b]thieno[3,2-b]pyridine-3,2′-benzo[b]thiophene] is described and a mechanism for the cyclisation is proposed.     

Alkylation of the 2-hydroxypyridine anion in ionic liquid media

The alkylation reaction of the ambident 2-hydroxypyridine anion was examined in ionic liquid media. Ionic liquids increase the alkylation reaction rate in comparison with molecular liquids, as well as the level of impact on the reaction rates of the counter ion and/or additives, and the distribution of isomers of the reaction products in trans-formations of the ambident 2-hydroxypyridine anion. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 699–710, May, 2008.