One-step synthesis of substituted 6-amino-5-cyanospiro-4-(piperidine-4')- 2H,4H-dihydropyrazolo[3,4-b]pyrans

Three-component condensation of 4-piperidinones (7), 5-pyrazolones (8), and malononitrile (4) proceeds chemically and electrochemically and is a convenient one-step means of synthesis of substituted 6-amino-5-cyanospiro-4-(piperidine-4')-2H,4H-dihydropyrazolo[3,4-b]pyrans (12). The electrochemical reactions proceed under milder conditions and with yields 12-15% greater than those of the reactions catalyzed by chemical bases.     

From atomistic lattice-gas models for surface reactions to hydrodynamic reaction-diffusion equations

Atomistic lattice-gas models for surface reactions can accurately describe spatial correlations and ordering in chemisorbed layers due to adspecies interactions or due to limited mobility of some adspecies. The primary challenge in such modeling is to describe spatiotemporal behavior in the physically relevant "hydrodynamic" regime of rapid diffusion of (at least some) reactant adspecies. For such models, we discuss the development of exact reaction-diffusion equations (RDEs) describing mesoscale spatial pattern formation in surface reactions. Formulation and implementation of these RDEs requires detailed analysis of chemical diffusion in mixed reactant adlayers, as well as development of novel hybrid and parallel simulation techniques. (c) 2002 American Institute of Physics.     

Double-quantum dipolar recoupling at high magic-angle spinning rates

A full investigation of the possible homonuclear double-quantum recoupling sequences, based on the RN family of sequences with N < or = 20, is given. Several new RN sequences, R16(6)(5), R18(8)(5), and R18(10)(5), were applied at high magic-angle spinning rates and compared with theory. The R18(10)(5) technique can be used to recouple dipolar couplings at spinning rates up to 39 kHz, and the application of the sequence in an INADEQUATE experiment is shown for a spinning rate of 30 kHz.     

Synthesis of arene-soluble mixed-metal Zr/Ce,Zr/Y,and related [[Zr2(OiPr)9]LnX2]n complexes using the dizirconium nonaisopropoxide ligand

The utility of polydentate monoanionic [Zr2(OiPr)9]- in generating arene-soluble, unsolvated, mixed-metal Zr/Ce and Zr/Y complexes is described. The synthesis of other mixed-metal zirconium lanthanide complexes was also studied to explore the relationship of metal size to structure. Lanthanide trihalides react in THF with KZr2(OiPr)9 to form unsolvated dimers, [[Zr2(OiPr)9]LnCl2]2, with the larger metals, Ln = Ce (1), Ho (2), Y (3), and unsolvated monomers, [Zr2(OiPr)9]LnCl2, with the smaller elements, Ln = Er (4), Yb (5). The synthesis of a monomeric iodide analogue, [Zr2(OiPr)9]TmI2, 6, by reduction of Zr2(OiPr)8(iPrOH)2 with TmI2(DME)3 is also reported. In all of these complexes, the [Zr2(OiPr)9]- subunit is tetradentate. 1-6 are compared with related cyclopentadienyl halide complexes to evaluate the special features of the dizirconium nonaisopropoxide ligand versus cyclopentadienide.     

Fluorination of thiocarbonyl compounds with Bis(2-methoxyethyl)aminosulfur trifluoride (Deoxo-fluor reagent): A facile synthesis of gem-difluorides

A variety of thiocarbonyl derivatives (thioketone, thioester, thioamide, dithioester, and dithiocarbamate) were converted to the corresponding gem-difluorides in excellent yields on reaction with the fluorinating agent, bis(2-methoxyethyl)aminosulfur trifluoride, in the presence of SbCl(3).     

Enantiospecific and regioselective rhodium-catalyzed allylic alkylation: diastereoselective approach to quaternary carbon stereogenic centers

The enantiospecific and regioselective rhodium-catalyzed allylic alkylation of a series of chiral nonracemic allylic carbonates, followed by ozonolysis and reductive lactonization, provides a convenient route to optically active gamma-lactones. Sequential alkylation and reductive alkylation furnished the alpha-quaternary-beta-ternary substituted gamma-lactone derivative as a >/=10:1 mixture of diastereoisomers.     

On row-cyclic codes with algebraic structure

In this article, some row-cyclic error-correcting codes are shown to be ideals in group rings in which the underlying group is metacyclic. For a given underlying group, several nonequivalent codes with this structure may be generated. Each is related to a cyclic code generated in response, to the metrics associated with the underlying metacyclic group. Such codes in the same group ring are isomorphic as vector spaces but may vary greatly in weight distributions and so are nonequivalent. If the associated cyclic code is irreducible, examining the structure of its isomorphic finite field yields all nonequivalent codes with the desired structure. Several such codes have been found to have minimum distances equalling those of the best known linear codes of the same length and dimension.This work was presented in part at the First International Conference on Finite Fields, Coding Theory, and Advances in Communications and Computing, Las Vegas, Nevada, August, 1991.     

Field applied (FMD) computer simulation of the frequency doubled optical Stark effect

It is shown by field applied molecular dynamics computer simulation (FMD) of liquid water that the frequency doubled optical Stark effect is accompanied by novel second order rise transients which have no known counterpart in orientational theory, based on Langevin/Kielich functions. In the statistically stationary, post transient, steady state, correlation function have been computed which are intricately dependent on the frequency of the pump laser. These transients can be obtained experimentally by modifications of optical Stark effect apparatus for measurement on a femtosecond time scale.     

A second trivalent graph with 58 vertices and girth 9

The trivalent graph of girth 9 with 58 vertices discovered by N. L. Biggs and M. J. Hoare is not the only graph of this kind.