Diastereoselective total synthesis of (+)-13-stemarene by fourth generation methods: a formal total synthesis of (+)-18-deoxystemarin

The problem of constructing diastereoselectively the C/D ring system of stemarane diterpenes from a bicyclo[2.2.2]octane intermediate was solved resulting in very simple synthesis of (+)-13-stemarene 1. The obtaining of the latter represents also a formal synthesis of (+)-18-deoxystemarin 2. In the key step, the epimeric mixture 10, dissolved in toluene, was converted by the action of TsOH into (+)-stemar-13-en-15-one 28.     

Campestarenes: novel shape-persistent Schiff base macrocycles with 5-fold symmetry

A simple 1-step procedure yields a family of easily modifiable, stable, conjugated Schiff base macrocycles with 5-fold symmetry mediated by 3-center hydrogen bonding.     

Theoretical reconstruction and elementwise analysis of photoelectron spectra for imidazolium-based ionic liquids

We have recently measured core level and valence band XPS, UPS, and MIES spectra of two room temperature ionic liquids composed of bis(trifluoromethylsulfonyl)imide anions ([Tf(2)N](-)) and either 1-ethyl-3-methyl-imidazolium ([EMIm](+)) or 1-octyl-3-methyl-imidazolium cations ([OMIm](+)). [T. Ikari, A. Keppler, M. Reinm?ller, W. J. D. Beenken, S. Krischok, M. Marschewski, W. Maus-Friedrichs, O. H?fft and F. Endres, e-J. Surf. Sci. Nanotechnol., 2010, 8, 241.] In the present work we analyze these spectra by means of partial density of states (pDOS) as calculated from a single ion pair of the respective ionic liquid using density functional theory (DFT). Subsequently we reconstruct the XPS and UPS spectra by considering photoemission cross sections and analyze the MIES spectra by pDOS, which provides us decisive hints to the ionic liquid surface structure.     

Surfactant effects on the reaction of 2‐(4‐cyanophenoxy)‐quinoxaline with hydroxide ion

A reaction of 2‐(4‐cyanophenoxy)quinoxaline 1 with hydroxide ion is accelerated by supramolecular aggregates of cetyltrialkylammonium chlorides (alkyl = Me, n‐Pr, and n‐Bu). In diluted surfactant solutions, with relatively high substrate concentration (7.0 × 10^?5 M), rate constants go through double rate maxima with increase in the surfactant concentration. The first rate maximum is ascribed to a reaction occurring in premicellar aggregates and the second to reaction in micelles. At low substrate concentration (7 × 10^?6 M), second‐order rate constants in the micellar pseudophase are dependent on the surfactant headgroup size, which is related to charge dispersion in the transition state. Nonmicellizing tri‐n‐octylmethylammonium ions (TOAMs) increase the reaction of 1 with hydroxide ion. The observed rate enhancements may be due to the formation of small, hydrophobic aggregates which bind the substrate and promote the nucleophilic substitution reaction. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 510–515, 2006     

Support properties and Holmgren's uniqueness theorem for differential operators with hyperplane singularities

Let W be a finite Coxeter group acting linearly on Rn. In this article we study the support properties of a W-invariant partial differential operator D on Rn with real analytic coefficients. Our assumption is that the principal symbol of D has a special form, related to the root system corresponding to W. In particular the zeros of the principal symbol are supposed to be located on hyperplanes fixed by reflections in W. We show that conv(suppDf)=conv(suppf) holds for all compactly supported smooth functions f so that conv(suppf) is W-invariant. The main tools in the proof are Holmgren's uniqueness theorem and some elementary convex geometry. Several examples and applications linked to the theory of special functions associated with root systems are presented.     

Determination of biogenic halogenated methyl-phenyl ethers (halogenated anisoles) in the picogram m -3 range in air

Halogenated anisoles (methyl-phenyl ethers) appear to be ubiquitous organic trace compounds in the environment. An analytical method is presented for analyzing the altogether 134 congeners of chloro-, bromo- and mixed bromochloro-anisoles on an isomer-specific basis in air. High volume sampling (20 m³ per hour) is carried out by adsorption, using a mixture of silica gel 60 and ENVI-Carb. The preseparation of the anisoles is achieved by NP-LC on Florisil (a magnesium silicate). The interference by volatile n-alkyl nitrates in the electron-capture detection can be avoided by a LC-preseparation on a carboneous phase. The isomer-specific separation and detection is performed by HRGC-ECD and HRGC-MS-SIM. A structure-specific systematic numbering of the 134 congeners of the chloro-, bromo- and bromochloro-anisoles is suggested. The retention data are given of 16 chloroanisoles, 10 bromoanisoles and 27 bromo-chloroanisoles on three stationary phases with different polarity.