Organoboron compounds,synthesis of allyl(dialkyl)boranes and diallyl(alkyl)boranes

Highly reactive allyl(dialkyl)-, crotyl(dialkyl)-, 3,3-dimethylallyl(dialkyl)-(= prenyl(dialkyl), and diallyl(alkyl)-boranes were prepared by allylation of esters R₂BOR′, RB(OR′)₂ or thioesters R₂BSR′ (R = alkyl) using allylic derivatives of aluminium, magnesium or boron in exchange reactions.The titled compounds are stable up to 100°C and do not symmetrize even on heating at 100°C for a long time. PMR spectroscopy data show that the characteristic feature of these compounds is a permanent allyl rearrangement, the rate of which increases with an increase in temperature. For allyl(diethyl)-borane at 100°C and 125°C the rates are equal to 2500 and 5000 sec^?1 respectively; activation energy of the rearrangement amounts to 11.8±0.2 kcal mol^?1.The boronallyl bonds in unsymmetrical allyl(alkyl)boranes readily split under the action of water and alcohols, protonolysis being accompanied by allyl rearrangement, crotyl and prenyl compounds are converted into 1-butene or 3-methyl-1-butene, respectively.     

Separation of C60 and C70 fullerenes on silica modified by polyaromatic and π-acid aromatic compounds

Separation of C₆₀ and C₇₀ fullerenes by HPLC was studied using sorbents synthesized by reaction of perylenedicarboxylic anhydride, dimethoxyviolanthrene, the tetramer of chromotropic acid with formaldehyde (TCA), trinitrobenzoyl chloride, or chlorotrinitrobenzene with γ-aminopropyl silica. These sorbents possess satisfactory chromatographic properties. The sorbent based on TCA is effective for separation of preparative amounts of fullerenes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1544–1546, August, 1997.     

Unique stereochemistry of 3-borabicyclo[3.3.1]nonane derivatives

The conformational equilibrium in solution was examined by NMR spectroscopy for a series of 7-phenyl-3-borabicyclo[3.3.1]nonane derivatives containing various substituents at the boron atom. The structures of these derivatives were studied in the crystalline state (X-ray diffraction analysis) and by quantum-chemical calculations (B3Pw91/6-31G*). The B...Ph transannular interactions corresponding to charge transfer from the system of the phenyl group to the vacant p-orbital of the B atom were demonstrated to be responsible for unique stability of the chair-chair conformation of these derivatives.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1884–1896, September, 2004.     

Stereoselective synthesis of (±)-indolizidines 167B and 209D and theirtrans-isomers based on the reductive allylboration of pyridine

A general method for the synthesis of 5-substituted indolizidines based on intramolecular cyclization oftrans- andcis-2-allyl-6-R-1,2,3,6-tetrahydropyridines, obtained from pyridine and triallylborane, has been elaborated. The closure of the five-membered ring is carried out by hydroboration-oxidation followed by cyclization of the resulting δ-amino alcohols in the presence of the Ph₃P−CBr₄−Et₃N system. (Pr₂BH)₂ and Pr₃B are used as the hydroborating reagents, and H₂O₂ in an acid medium is used for the oxidation of 2-[3-(dipropylboryl]-Δ²-piperideines formed. This method has been used for the synthesis of two natural alkaloids: indolizidine 209D (cis-5-hexylindolizidine) and itstrans-isomer were prepared fromcis- andtrans-2-allyl-6-hexyl-1,2,3,6-tetrahydropiridine, respectively; indolizidine 167B andtrans-5-propylindolizidine were synthesized fromcis- andtrans-2,6-diallyl-1,2,3,6-tetra-hydropyridine, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 971–979, May, 1998.     

EPR of copper(II) chloride complexes with diphosphine dioxides

Stepwise formation of copper(ll) chloride complexes with diphosphine dioxides has been studied using paramagnetic resonance. It was found that in complexes with a copper:ligand composition of 11 substituents have little effect on parameters of the anisotropic EPR spectra. The spectra of complexes with a metal:ligand composition of 12 are considerably more sensitive to the introduction of substituents; this is explained by sterically dependent differences in the structure of the complexes. The possibility of trisligand complexes being formed is evidently largely determined by the size of the groups on the phosphorus atoms.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 362–368, February, 1991.     

ESR study of free radicals formed upon UV irradiation of nitropentafluoroacetone in various solvents

The formation of CF₃C(O)CF₂N(O^.)O₂CF₂C(O)CF₃ free radicals upon the UV irradiation of nitropentafluoroacetone (1) in toluene and mesitylene is established by ESR. The most likely cause of their formation is the one-electron oxidation of the solvents by photoexcited1 followed by decay of the radical anion formed from1 with the expulsion of an NO₂ anion and attachment of the radical to a molecule of original1. The irradiation of 1 in triethylsilane results in the elimination of a fluoride ion and fixation of a CF₃COCFN(O^–)O' radical. UV irradiation of ketone1 in pentane results in the abstraction of a hydrogen atom from the solvent and the formation of a CF₃COCF₂N(OH)O ' radical.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 512–514, March, 1993.     

New antiferroelectric liquid crystalline materials containing a keto group and two lactate groups

New chiral liquid crystalline materials containing a keto group and two lactate units attached to the mesogenic core have been synthesized and studied. All the new compounds show the paraelectric SmA, ferroelectric SmC* and antiferroelectric SmC*_A phases each over rather broad temperature ranges. The properties of the phases were characterized by DSC, electro-optical and dielectric studies. The spontaneous polarization, tilt angle, helical pitch, and switching times were determined for the polar phases.     

Specifics of scattering of nonrelativistic electrons in nanosized films

The specifics of energy exchange by nonrelativistic electrons (electron energy of ∼10²–10³ eV) during their travelling through a dielectric layer have been studied depending on the thickness of the layer applied on substrates with different parameters. Electron travelling across a dielectric (pyrene) layer with a thickness of up to 10 nm deposited on a metal (bismuth) mirror is accompanied by the following effects dependent on the dielectric-layer thickness and the electric parameters of the boundary: a nonmonotonic change in the pyrene luminescence intensity and variation in secondary electron emission.