Victor B. Rybakov

Duality of Donor–Acceptor Cyclopropane Reactivity as a Three‐Carbon Component in Five‐Membered Ring Construction: [3+2] Annulation Versus [3+2] Cycloaddition

Quo vadis? The Lewis acid catalyzed reaction of (hetero)aryl-derived donor-acceptor cyclopropanes with alkenes can be selectively directed along a [3+2] annulation pathway (see scheme). This new process provides convenient and efficient access to indanes and other cyclopentannulated (hetero)arenes, among which polyoxygenated 1-arylindanes exhibit significant cytotoxicity against several cancer cell lines with an IC50 of 10(-6)-10(-5)  M.

Structure analysis of the cubic boron nitride crystals

Abstract Cubic BN crystals grown in different growth systems were studied by X-ray diffraction, IR and EPR spectroscopy methods. The unit cell parameters of the crystals and the thermal vibrations of B and N sublattices were determined.

X-ray Diffraction Study of the Structure and Defect System of Yb-Activated (Na0.5Gd0.5)WO4 Crystals

Nominally pure and Yb-activated Czochralski-grown (Na0.5Gd0.5)WO4 crystals (scheelite type) were studied by x-ray diffraction (phase analysis, unit-cell parameters, and structure refinement by the Rietveld method and single-crystal techniques). A pseudotetragonal (orthorhombic) superstructure was revealed, which was shown to have doubled unit-cell parameters compared to the scheelite cell. Some of the crystals were found to contain tungsten and oxygen vacancies, which give rise to additional optical absorption. The effects of the growth and heat-treatment conditions and Yb activation on the structure, defect system, and additional absorption spectrum of (Na0.5Gd0.5)WO4 are analyzed.

From Umpolung to Alternation: Modified Reactivity of Donor–Acceptor Cyclopropanes Towards Nucleophiles in Reaction with Nitroalkanes

A conceptually new type of donor-acceptor cyclopropane reactivity towards nucleophiles has been disclosed. An essential characteristic of the process is an unusual nucleophilic attack on the C(3)-position of a cyclopropane, combined with typical small ring-opening by cleavage of the C(1)-C(2) bond between the acceptor and the donor. Based on this new reaction between cyclopropane-1,1-diesters and nitroalkanes, we developed a convenient approach to γ-nitroesters that can be efficiently transformed to the substituted pyrrolidones, structural analogues of racetame family drugs (rolipram, phenylpiracetam, etc.).

Reaction of Corey ylide with α,β-unsaturated ketones: tuning of chemoselectivity toward dihydrofuran synthesis.

A straightforward, efficient, and reliable approach to synthetically valuable 2,3-dihydrofurans via a reaction between Corey ylide and α,β-unsaturated ketones has been developed. The use of simple and widely spread starting materials as well as mild reaction conditions and scalability provide a broad scope of 2,3-dihydrofurans.

Growth and X-ray diffraction study of YCa4O(BO3)3:Ce, Er, Yb crystals

YCa4O(BO3)3crystals (sp. gr. Cm), nominally pure and activated with Yb, Er, and/or Ce, were grown by the Czochralski technique. The crystal structure of YCa4O(BO3)3was refined by single-crystal x-ray diffraction, and the site compositions were determined: (Y0.792Ca0.208(6) )(Ca0.938Y0.062(4) )2Ca2O0.96(2)[ ]0.04(BO3 )3([ ] = vacancy). The data set for YCa4O(BO3)3was found to contain additional reflections which were inconsistent with space group Cmbut could be indexed in a cell with doubled a. No superlattice reflections were detected in the case of the activated crystals. Structural data for LnCa4O(BO3)3were used to derive relations for the lattice parameters and average cation–anion distances as functions of rLnand weighted-average cation radii on the mixed-occupancy sites, which made it possible to assess the distributions of Y, Yb, Er, Ce, and Ca over the mixed-occupancy sites. Absolute structure determination showed that the pure and Yb3+-activated YCa4O(BO3)3crystals differed in polarity.

Three-Component Heterocyclization of gem-Bromofluorocyclopropanes with NOBF4: Access to 4-Fluoropyrimidine N-Oxides

Novel three-component heterocyclization involving gem-bromofluorocyclopropanes, nitrosyl tetrafluoroborate, and a molecule of the solvent (nitrile) yielding previously unknown fluorinated pyrimidine N-oxides is described. A two-step synthetic approach to 4-fluoropyrimidine N-oxides from alkenes under mild conditions is developed using this reaction. Mechanistic aspects of the heterocyclization are discussed.

Composition, structural parameters, and color of langatate

Langatate crystals with the nominal composition La3(Ga0.5Ta0.5)Ga5O14 grown by Czochralski pulling along 〈0001〉 have been studied by X-ray and neutron diffraction before and after postgrowth annealing in air and vacuum. Their compositions are determined, the relationship between the Ga/Ta ratio and unit-cell parameters is established, and their color (colorless, yellow, and orange crystals) is shown to depend on their oxygen content and the growth and annealing conditions. Vacuum annealing at sufficiently high temperatures leads to precipitation of a green phase, La(Ta,Ga)3+O3.

Indirect Competitive Immunoassay for Detection of Vitamin B2 in Foods and Pharmaceuticals

An indirect immunoassay for the determination of vitamin B2 in food samples and vitamin tablets was developed. A carbodiimide-modified active ester method was used to synthesize the immunogen for vitamin B2. The coupling ratio of vitamin B2 to carrier protein in immunogen was 19.98:1. The titer of the polyclonal antibody was 1:64000, and the antibody showed high specificity in the presence of vitamin B2 photolytic products and other B group vitamins. The immunoassay showed detection limits (LODs) of 1.07 ng/mL in PBS, 24.6 ng/g in vitamin drink, and 0.50 mg/kg in milk powder. Recovery was 99.58-110.91% in milk powder and 70.20-100.5% in vitamin drink. Vitamin B2 samples were analyzed by high-pressure liquid chromatography (HPLC) and the immunoassay, and results showed good agreement. Finally, this method was applied to detect vitamin B2 in commercial milk powder and vitamin tablets, and the detected amount correlated well with the labeled amount.

Symmetry of (Na0.5R0.5)MO4 crystals (R = Gd, La; M = W, Mo)

AbstractKinetic order-disorder phase transitions (space group space group