TiCl4-catalyzed indirect anti-Markovnikov hydration of alkynes: application to the synthesis of benzo[b]furans

An efficient methodology for the indirect anti-Markovnikov hydration of unsymmetrically substituted terminal and internal alkynes is based on TiCl4-catalyzed hydroamination reactions. Its application to ortho-alkynylhaloarenes, followed by a copper-catalyzed O-arylation, provides flexible access to substituted benzo[b]furans.     

Modelling of closed-chain manipulators on an excavator vehicle

The main focus of this paper is to develop a physics-based model for a closed-chain manipulator in an excavator vehicle. The derivation of closed-chain manipulator dynamic equations with a structure similar to open-chain manipulator equations is an important research problem, particularly with reference to controller design. In this paper, an approach for deriving closed-chain manipulator equations with an open-chain structure, based on trigonometric t-formulae, is presented. Holonomic loop closure constraints are employed in order to derive the closed-chain mechanism dynamics from the reduced system dynamics. The closed-chain equations, with a structure similar to serial link equations, are presented. The model incorporates the dynamic properties of the manipulator and bucket. The dynamic model for the excavation system is validated against measured data obtained from a full-scale closed-chain excavator vehicle. A dynamic model is important for the design of control strategies for trajectory tracking, a key requirement for automating the excavation task. It is noted that even though the results presented in this paper are focused on a particular excavator vehicle, the research is generic and can be adapted to any closed-chain manipulator.     

In-situ imaging of the nucleation and growth of epitaxial anatase TiO2(001) films on SrTiO3(001)

The growth of TiO₂ anatase films on Nb‐doped SrTiO₃(001) molecular beam epitaxy has been studied in-situ by scanning tunneling microscopy. We show that the initial growth follows the Stranski–Krastanov mode, where islands form on top of a wetting layer consisting of two monolayers (ML) of TiO₂. The epitaxial islands subsequently nucleate and coalesce into large commonly oriented crystallites. The reconstruction observed by reflection high-energy electron diffraction (RHEED) is shown to result from the coexistence of individual (4 × 1) and (1 × 4) reconstructions present on different crystallite surfaces. The anatase grows in units of bilayers, resulting in a step height of 2 ML (~ 0.5 nm). This result explains the fact that the measured period of the RHEED specular-beam intensity oscillations corresponds to the time required for deposition of 2 ML. Ar ion sputtering and UHV annealing results in a transformation to coexisting (4 × 1) and (1 × 4) reconstructed terraces on individual crystallites, as commonly observed by ex-situ STM studies.     

Grating coupled interferometry for optical sensing

An interferometric sensor based on gratings on a planar waveguide is introduced. The device combines the advantages of known interference-based waveguide sensors with the simplicity of grating couplers. In the presented configuration, two parallel and coherent light beams, laterally separated in the direction of mode propagation, are coupled into a planar waveguide through a grating. One of the coupled beams is phase modulated using a periodically relaxing liquid crystal modulator, resulting in a time varying intensity signal at the end face of the waveguide. Refractive index changes within the waveguide section between the two coupling regions are monitored by observing characteristic changes in the intensity signal.     

1,3‐Diaxial Repulsion vs. π‐Delocalization in the 7‐Amino‐2,4‐diazabicyclo[3.3.1]nonan‐3‐one Skeleton

(1R,5S,6S,8R)‐6,8,9‐Trihydroxy‐3‐oxo‐2,4‐diazabicyclo[3.3.1]nonan‐7‐ammonium chloride hydrate ( 3 Cl⋅H₂O) and (1R,5S,6S,8R)‐7‐amino‐6,8,9‐trihydroxy‐2,4‐diazabicyclo[3.3.1]nonan‐3‐one ( 4 ) have been prepared, and their crystal structures have been determined from single‐crystal X‐ray diffraction data. Both compounds consist of a bicyclic skeleton with the three N‐atoms in an all‐cis‐1,3,5‐triaxial arrangement. Considerable repulsion between these axial N‐atoms is indicated by a significant distortion of the two cyclohexane chairs and by increased N⋅⋅⋅N distances. The lone pair of the free amino group of 4 is involved in intermolecular H‐bonding and is turned away from the adjacent carbonyl C‐atom of the urea moiety. The structural properties together with the observed reactivity do not provide any evidence for an intramolecular donor‐acceptor interaction between the carbonyl C‐ and the amine N‐atom.     

Tilcotil® Studies [3+2] additions with isothiazol-3(2H)-one 1,1-dioxide

Derivatives of isothiazol-3(2H)-one 1,1-dioxide react regiospecifically with 1,3-dipolar agents. The main regiocontrolling factor is ascertained to be the C?O group of the dipolarophile. The topology of the adducts is also in general agreement with predictions based on perturbation theory. Several adducts can be aromatized to heterocyclic equivalents of saccharin, and may then be elaborated into structural analogs of tenoxicam (Tilcotil® and piroxicam (Feldene®)).     

Lifetime of the two-phonon vibrational state in232Th

We report on a measurement of the lifetime of the 1414 keV state in²³²Th by the Doppler-shift recoil-distance method. This 4⁺ state shows all characteristics of a nearly-harmonic two-phonon-vibrational excitation. The result for the B(E2) value obtained from the lifetime,=3.2 ± 0.7 ps, is in agreement with an earlier estimate of the collectivity from Coulomb-excitation yields and supports the interpretation of the 1414 keV state as a two-phonon-vibrational excitation.We would like to thank the accelerator crew of the Max-Planck-Institut für Kernphysik for the excellent running conditions they maintain. We are also indebted to Dr. H.J. Maier, University Munich for supplying us with the²³²Th targets. This work was supported by the Bundesminister für Forschung und Technologie under contract numbers 06BN601 and 06HD5251.     

Alkenediazonium Salts: A New Chapter of Classical Organic Chemistry

Whereas the protonation of α-diazo-β-diketones and α-diazo-β-oxo esters with hydrogen chloride and antimony pentachloride yields the corresponding hydroxyalkenediazonium hexachloroantimonates, the “acid-sensitive” α-diazomonocarbonyl compounds can be transformed into resonance-stabilized alkenediazonium salts by an analogous O-alkylation with triethyloxonium hexachloroantimonate. A general route for synthesizing these compounds consists in the transformation of the p-toluenesulfonylhydrazones of α-halogenated aldehydes and ketones with Lewis acids. Alkenediazonium ions which are not resonance stabilized can be isolated at room temperature only if their decomposition at higher temperatures leads, via evolution of nitrogen, to vinyl cations in particularly high energy levels. Facile substitution reactions at the CC double bond with anisole and methanol demonstrate the strongly electrophilic nature of alkenediazonium salts. When electron-donating substituments are attached to C2 of an ethylenediazonium ion, the bond order of the NN triple bond can be reduced to a level comparable with that in diazoacetic ester.     

Three-component indole synthesis using ortho-dihaloarenes

A three-component synthesis of substituted indoles is accomplished starting from ortho-dihaloarenes through the use of a multicatalytic system consisting of an N-heterocyclic carbene palladium complex and CuI. The corresponding indole derivatives are obtained as single regioisomers in high yields of isolated product.