Monatshefte für Chemie und verwandte Teile anderer Wissenschaften

 A short facile synthesis of the fungal metabolite (±)-3,4-dihydro-3,6,8-trihydroxy-3- pentadecylisocoumarin (peniolactol) has been achieved. Condensation of hexadecanoyl chloride with 3,5-dimethoxyhomophthalic acid afforded 6,8-dimethoxy-3-pentadecylisocoumarin, which on sequential saponification and demethylation furnished rac-peniolactol in 31% overall yield. The ring-chain tautomerism was studied in solution by 1H NMR and the mass fragmentation pattern. 3-Pentadecyl- isocoumarin was also synthesized and saponified to the corresponding keto acid as a model compound for comparative studies.

 The solution structure of two natural diterpene derivatives, the secondary metabolites esulatin-A and esulatin-B of Euphorbia esula, was investigated by homonuclear NMR experiments. Since the spectral dispersion of the 1H NMR spectra at 500 MHz was sufficient to separate several skeletal protons of the title compounds, they were selectively excited with a double pulsed field gradient spin-echo (DPFGSE) sequence using 180°Gaussian pulses sandwiched between sine shaped gradients. With the use of selective excitation, scalar as well as dipolar interactions of the selected spins were monitored through one-dimensional (1D) COSY, TOCSY, and NOESY experiments. The chemical shifts of the coupling partners could be accurately extracted from the 1D COSY and TOCSY spectra recorded with high digital resolution. The selective TOCSY experiment provided an excellent opportunity to identify spins belonging to the same scalarly coupled spin system. The solution state conformation was investigated by selective gradient enhanced NOESY experiments. Proton–proton distances were evaluated from the cross-relaxation rates obtained from a quantitative analysis of the NOESY spectra recorded with different mixing times. The NMR derived distances were compared to the results of solid state X-ray diffraction measurements.

Using the cluster model of the silicon (111) surface we derive by means of EHT calculations a mechanism of reactive plasma etching in the system F/Si including diffusion processes. Species SiF2 are found to be the primary etching products at the surface. SiF4 is formed with high probability in the gas phase.

The weight average degree of polymerization of vinyl acetate-divinyl adipate copolymers (low content of divinyl adipate) is measured at conversions up to 22%. From thisk 13/k 12 (rate constants of reaction of growing radicals with pendent double bonds and divinyl adipate double bonds, respectively) is calculated to be 0.28. A quantitative relation for the gel point (critical conversion) is given.

Reaction of nitrogen-containing acetals with aromatic compounds is a valuable method of synthesis of various heterocycles. Herein we report the study on the reaction of (4,4-diethoxybutyl)ureas with nucleophilic aromatics. We have found that the structure of the products mainly depends on the strength of the acid used as catalyst as well as aromatic nucleophile nature and its concentration. Either 2-arylpyrrolidines, diarylbutanes, bispyrrole derivatives, or pyrrolidinequinazolinones can be synthesized via variation of these factors. The proposed mechanism of the reaction is discussed.