Preparation of fully substituted anilines for the synthesis of functionalized indoles

A wide range of highly functionalized indoles were prepared by the successive magnesiation of readily available o-alkynyl protected anilines using TMPMgCl.LiCl or LDA, followed by a KH-mediated cyclization reaction.     

Analytical approximations for the solution of chance constrained optimization problems

Uncertain influences are inherent in many practical processes, stemming for instance from measurement errors in process optimization or missing knowledge about the future behavior of a given system, e.g., the financial markets. Therefore, it is desirable to explicitly consider uncertainties when optimizing such processes. One possible approach for this task is the usage of chance constrained optimization (CCOPT), which allows that the constraints are only held with a certain probability level. This enables the user to make a compromised decision between reliability and profitability. Solving CCOPT problems usually consists of two steps. First, transforming the chance constraints into deterministic ones and then solving the transformed problem with a standard NLP solver. Depending on the underlying process, several approaches exist for the transformation. Here, we investigate the usage of so called analytical approximations (AAs). In general, AA approaches do not lead to an exact deterministic representation of CCOPT problems. Nonetheless, it can be shown that a solution obtained by AA is always feasible for the original problem. Furthermore, the corresponding optimization problem generated by AA is computationally more tractable than the original formulation, making these approaches interesting for larger scale processes. We propose a new AA method and present a comparison with existing AA approaches, considering efficiency and suitability. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wall-impinging laminar premixed n-dodecane flames under autoignitive conditions

Laminar one-dimensional (1D) flames in a stagnation flow stabilised at a wall are used to study flame–wall interaction under diesel engine conditions. The thermochemical conditions correspond to that of the Engine Combustion Network (ECN) Spray A reference case. A range of inflow velocities is considered, where the lowest inflow velocity is chosen such that the flame is detached from the inlet. The presence of a wall is shown to have a significant impact on the flame structure and emission formation. The 1D flame and homogeneous reactor results exhibit two distinct reaction zones due to low- and high-temperature chemistry (LTC and HTC, respectively). The burner-stabilised flames are overall dominated by autoignition for all inflow velocities. For the impinging jet flames, the response of the LTC reaction zone follows closely that of the burner-stabilised flames up to relatively high inflow velocities. The HTC reaction zone, however, deviates strongly from the burner-stabilised flames, already at low inflow velocities and quenches at high inflow velocities. A budget analysis revealed a strong contribution from diffusion in the HTC reaction zone, resulting in an increasing importance of deflagrative combustion as opposed to autoignition. This trend was attributed to enhanced strain rates at higher inlet velocity leading to higher gradients. Wall heat transfer was also investigated. The highest wall heat transfer rates were observed for mixtures between $\Phi =1.0$ and $\Phi =1.5$ and for inlet velocities just below the quenching limit. This was attributed jointly to the higher peak product temperatures for these mixtures and to their enhanced resilience to quenching under strain which leads to higher temperature gradients at the wall just before quenching. NO formation was studied. The highest NO formation was observed near $\Phi =1.0,$ though the response to strain rate was different for stoichiometric and rich mixtures, which was attributed to differing NO formation pathways.     

Volume integral equations for scattering from anisotropic diffraction gratings

We analyze electromagnetic scattering of transverse magnetic polarized waves from a diffraction grating consisting of a periodic, anisotropic, and possibly negative index dielectric material. Such scattering problems are important for the modelization of, for example, light propagation in nano‐optical components and metamaterials. The periodic scattering problem can be reformulated as a strongly singular volume integral equation, a technique that attracts continuous interest in the engineering community but has rarely received rigorous theoretic treatment. In this paper, we prove new (generalized) Gårding inequalities in weighted and unweighted Sobolev spaces for the strongly singular integral equation. These inequalities also hold for materials for which the real part of the material parameter takes negative values inside the diffraction grating, independently of the value of the imaginary part. Copyright © 2012 John Wiley & Sons, Ltd.     

Light scattering study on the glass former o-terphenyl

Combining double monochromator, tandem Fabry-Pérot interferometry (TFPI), and photon correlation spectroscopy (PCS), the full range of the dynamic susceptibility of the glass former o-terphenyl is covered (240-440 K). A time resolution of 6 ns is reached by the PCS setup, and the measuring gap between PCS and TFPI has significantly shrunk. Combined time domain data are presented, which cover 0.01 ps-100 s. Regarding the primary α-process, no recognizable change in shape and amplitude is observed, i.e., frequency-temperature superposition holds over the entire temperature range investigated. The only change in the susceptibility is the emergence of the excess wing contribution, leading to a flattening of the susceptibility minimum close to T(g). Separating relaxation contribution from fast and slow dynamics, we determine the relaxation strength 1-f(rel)(T) of the fast dynamics, which shows a cusplike temperature dependence with a crossover temperature T(c)=316±10 K. Due to relative small changes of 1-f(rel)(T) the effect is difficult to identify in f(rel)(T) itself. The crossover temperature is larger than previously reported as no extrapolation scheme is applied.     

On the survival probability of a random walk in a finite lattice with a single trap

We consider the survival of a random walker in a finite lattice with periodic boundary conditions. The initial position of the random walker is uniformly distributed on the lattice with respect to the trap. We show that the survival of a random walker, U _n>, can be exactly related to the expected number of distinct sites visted on a trap-free lattice by U _n=1–S _n/N ^D (*) whereN ^D is the number of lattice points inD dimensions. We then analyze the behavior of S_n in any number of dimensions by using Tauberian methods. We find that at sufficiently long times S _n decays exponentially withn in all numbers of dimensions. InD = 1 and 2 dimensions there is an intermediate behavior which can be calculated and is valid forN ²N 1 whenD = 1 andN lnN n 1 whenD = 2. No such crossover exists when Z3. The form of (*) suggests that the single trap approximation is indeed a valid low-concentration limit for survival on an infinite lattice with a finite concentration of traps.     

The structure of tricyclo[3.3.2.0]decane (hexahydrobullvalene) – A gas-phase electron diffraction (GED) study

The molecular structure of tricyclo[3.3.2.0^2.8]decane (hexahydrobullvalene) has been determined experimentally by gas-phase electron diffraction as well as by quantum chemical calculations. The bond lengths (twofold standard deviations in parentheses) in the skeleton [1.496(7) in the cyclopropane ring, 1.527(10) adjacent to it, 1.550(22) for the central bonds in the bridges and 1.548(16) Å for the bonds originating from the singular bridgehead] all can be explained in terms of the features of this cage hydrocarbon. All three CCC valence angles [113.0(8)° at the singular bridgehead, 112.8(12) adjacent to it and 122.3(20) adjacent to the skeletal cyclopropane ring] are larger than the regular tetrahedral angle on an sp³-hybridized carbon atom. The two-carbon bridges between the skeletal cyclopropane ring and the opposite bridgehead are twisted with a dihedral angle of 43(2)°, i.e. significantly less than the approximately 60° in n-butane in its synclinal (gauche) conformation.     

High harmonic imaging of few-cycle laser pulses

We show that the strength of the central electric field peaks in a few-cycle laser pulse can be recovered from a frequency-time image of the high harmonic spectrum generated in a gas volume. Pulse intensity, duration, and also the carrier-envelope phase phi(CE) can be determined. A simple and robust observable is defined that provides a gauge of phi(CE) for pulse durations up to three optical cycles, corresponding to 7.8 fs FWHM at the Ti:sapphire wavelength of 800 nm.     

Isocyanides in the synthesis of nitrogen heterocycles

Isocyanides have long proved themselves to be irreplaceable building blocks in modern organic chemistry. The unique features of the isocyano group make isocyanides particularly useful for the synthesis of a number of important classes of nitrogen heterocycles, such as pyrroles, indoles, and quinolines. Several cocyclizations of isocyanides via zwitterions and radical intermediates as well as transition-metal-catalyzed syntheses of different types of heterocycles have recently been developed. Methods starting from isocyanides often have distinct advantages over alternative approaches to the same heterocycles because of their enhanced convergence, the great simplicity of most of the operations with them, and the great variety of isocyanides readily available for use. Isocyanides have also been used in some enantioselective syntheses of chiral heterocyclic compounds, including natural products as well as precursors thereof.