Efficient synthesis of furan-2-ylacetates, 7-(alkoxycarbonyl)benzofurans, and 7-(alkoxycarbonyl)-2,3-dihydrobenzofurans based on cyclization reactions of free and masked dianions: a "cyclization/dehydrogenation" strategy

[reaction: see text] A variety of furan-2-ylacetates have been prepared by dehydrogenation of monocyclic 2-alkylidenetetrahydrofurans, which are readily available by cyclizations of open-chained 1,3-dicarbonyl dianions with 1-bromo-2-chloroethane. 5'H-[2,3']Bifuranyl-2'-ones are available based on sequential "cyclization/dehydrogenation" reactions of alpha-acetyl-gamma-butyrolactones. A variety of 7-(alkoxycarbonyl)benzofurans and 7-(alkoxycarbonyl)-2,3-dihydrobenzofurans were prepared by a cyclization/dehydrogenation strategy. These reactions rely on cyclizations of 2-oxocycloalkane-1-carboxylate-derived 1,3-dicarbonyl dianions ("free dianions") or 1,3-bis-silyl enol ethers ("masked dianions") with various 1,2-dielectrophiles.     

137Cs in Biota and Sediment Samples from Turkish Coast of the Black Sea, 1997–1998

During the periods of 1997–1998, macroalgae, sea snail, mussel, fish and sediment samples were collected from different stations at Turkish Black Sea coast in order to determine activity levels of ¹³⁷Cs radionuclide. ¹³⁷Cs activity in the tested algae species and in soft parts of mussel and sea snail, were found to be below the lower limit of detection. On the other hand, the ¹³⁷Cs concentration in muscle tissue of the sea snail samples were found from 6±2 to 19±7 Bq·kg^–1 dry weight. The range of the ¹³⁷Cs concentration in anchovy fish muscles were found between 4±2 – 10±5 Bq·kg^–1 dry weight. The ¹³⁷Cs concentration in the whiting fish muscle was found below the lower limit of detection. However, this activity found in shad fish muscle to be 25±10 Bq·kg^–1 dry weight. The concentrationsof the ¹³⁷Cs activity in the sediment samples proved that the eastern region of the Black Sea was affected by Chernobyl at a very high degree compared with the western part. The measured ²³⁸U, ²³²Th and ⁴⁰K concentrations in sediment samples are within the range of the cited values in the previous works at the Turkish Black Sea coast.     

Finite difference method combined with differential quadrature method for numerical computation of the modified equal width wave equation

The aim of this study is to improve the numerical solution of the modified equal width wave equation. For this purpose, finite difference method combined with differential quadrature method with Rubin and Graves linearizing technique has been used. Modified cubic B‐spline base functions are used as base function. By the combination of two numerical methods and effective linearizing technique high accurate numerical algorithm is obtained. Three main test problems are solved for various values of the coefficients. To observe the performance of the present method, the error norms of the single soliton problem which has analytical solution are calculated. Besides these error norms, three invariants are reported. Comparison of the results displays that our algorithm produces superior results than those given in the literature.     

Equilibration of a cone: KMC simulation results

We study the equilibration of an initial surface of conic shape that consists of concentric circular monolayers by Kinetic Monte Carlo (KMC) method. The kinetic processes of attachment and/or detachment of particles to/from steps, diffusion of particles on the surface, along a step or cluster edges are considered. The difference between an up hill and down hill motion of a particle at a step are taken into account through the Ehrlich-Schwoebel (ES) barrier. The height of the cone evolves as h(0) − h(t) ~ t ^1/α where h(0) is the initial height of the surface and α is approximately 2. The ES barrier slows down the equilibration of the surface but the time dependence remains as given above. The exponent α depends neither on ES barrier nor on the temperature. The equilibration is found also to be independent of energy barrier to the motion of particles along the step edges. The number of particles in each layer except the top two circular layers is found to decrease as t ^0.57.     

Synthesis of functionalized pyrroles and 6,7-dihydro-1H-indol-4(5H)-ones by reaction of 1,3-dicarbonyl compounds with 2-azido-1,1-diethoxyethane

The condensation of 1,3-dicarbonyl compounds with 2-azido-1,1-diethoxyethane and subsequent cyclization allowed an efficient synthesis of a variety of pyrroles and 6,7-dihydro-1H-indol-4(5H)-ones.     

Synthesis of benzofurans with remote bromide functionality by domino "ring-cleavage-deprotection-cyclization" reactions of 2-alkylidenetetrahydrofurans with boron tribromide

[reaction: see text] Bromination and subsequent Suzuki reactions of 2-alkylidenetetrahydrofurans, readily available by [3+2] cyclizations, afforded 1'-(2'-methoxyphenyl)-2-alkylidenetetrahydrofurans. Treatment of the latter with boron tribromide and subsequent addition of water resulted in the chemoselective formation of functionalized benzofurans containing a remote bromide functionality. The products are formed by a new domino "ring-cleavage-deprotection-cyclization" reaction. The addition of an aqueous solution of potassium tert-butoxide, rather than water, afforded saturated analogues of calycine by a "ring-cleavage-deprotection-ring-closure-lactonization" reaction.     

Solution properties of (co)polyvinylethynylpiperidols

Hydrodynamic properties of new ethynylpiperidol-based polyelectrolytes and polyampholytes were studied. Such conformational characteristics as constants of Mark-KuhnHouwink equations, unperturbed sizes, and the degree of polymer chain coiling were determined. The effect of ionic strength of solution, organic compound additions, and anion nature on molecular parameters of cationic polyelectrolytes was studied. Hydrodynamic properties of polymeric ampholytes near an isoelectric point were studied as a function of various factors. Polyampholyte macromolecules were shown to assume a compact conformation at the isoelectric point irrespective of the polymer chain length. Polyampholyte molecules unfolded at the isoelectric point with an increase of the ionic strength of the solution, which agreed with the assumption made previously.     

On the Range of Possible Integrities of Graphs G(n, k)

We discuss the range of values for the integrity of a graphs G(n, k) where G(n, k) denotes a simple graph with n vertices and k edges. Let I _max(n, k) and I _min(n, k) be the maximal and minimal value for the integrity of all possible G(n, k) graphs and let the difference be D(n, k) = I _max(n, k) − I _min(n, k). In this paper we give some exact values and several lower bounds of D(n, k) for various values of n and k. For some special values of n and for s < n ^1/4 we construct examples of graphs G _n  = G _n (n, n + s) with a maximal integrity of I(G _n ) = I(C _n ) + s where C _n is the cycle with n vertices. We show that for k = n ²/6 the value of D(n, n ²/6) is at least \frac?6-13n{\frac{\sqrt{6}-1}{3}n} for large n.     

The possible effect of stratospheric quasi-biennial oscillation on the critical frequency of the ionospheric F2-layer

In this work, active control method is proposed for controlling and synchronising seven-dimensional (7D) hyperchaotic systems. The seven-dimensional hyperchaotic system is considered for the implementation. Seven-dimensional hyperchaotic system is also investigated via time series, phase portraits and bifurcation diagrams. For understanding the impact of active controllers on global asymptotic stability of synchronisation and control errors, the Lyapunov function is used. Numerical analysis is done to reveal the effectiveness of applied active control method and the results are discussed.     

Efficient synthesis of functionalized furans and benzofurans based on a ‘[3+2] cyclization/oxidation’ strategy

Functionalized furans and benzofurans were prepared by DDQ oxidation of 2-alkylidenetetrahydrofurans, which are readily available by one-pot cyclizations of 1,3-dicarbonyl dianions or 1,3-bis-silyl enol ethers.