Synthesis of (+)-(S)-Streptenol A and Biomimetic Synthesis of (2R,4S)- and (2S,4S)-2-(Pent-3-enyl)piperidin-4-ol

(+)-(S)-Streptenol A is synthesized by coupling a 1,3-dithiane with an optically pure epoxide. The absolute configuration of (+)-(S)-streptenol A is thereby correlated with that of (S)-malic acid. Stereoselective reduction of an oxime that could easily be prepared from streptenol A gave the (3S,5R)- and (3S,5S)-aminostreptenols, and after cyclization, configurationally pure 2,4-functionalized piperidine alkaloids.     

Inverse error propagation and model identification for coupled dynamic problems with application to electromagnetic metal forming

The purpose of this work is the development and application of strategies to identify material model parameters for metals at high strain-rates using data obtained from high-speed electromagnetic metal forming. To this end, a staggered algorithm for the finite-element-based numerical solution of the coupled electromagnetic-mechanical boundary-value problem has been developed based on mixed Eulerian–Lagrangian multigrid methods. On this basis, the parameter determination together with a sensitivity analysis and error estimation are carried out. After verifying the validity of this approach using synthetic data sets, it is applied to the identification of material parameters using experimental results from electromagnetic tube forming.     

A model-theoretic characterization of constant-depth arithmetic circuits

We study the class ${\mathrm{\#}\text{AC}}^0$ of functions computed by constant-depth polynomial-size arithmetic circuits of unbounded fan-in addition and multiplication gates. No model-theoretic characterization for arithmetic circuit classes is known so far. Inspired by Immerman's characterization of the Boolean circuit class ${\text{AC}}^0$, we remedy this situation and develop such a characterization of ${\mathrm{\#}\text{AC}}^0$. Our characterization can be interpreted as follows: Functions in ${\mathrm{\#}\text{AC}}^0$ are exactly those functions counting winning strategies in first-order model checking games. A consequence of our results is a new model-theoretic characterization of ${\text{TC}}^0$, the class of languages accepted by constant-depth polynomial-size majority circuits.     

Electron properties in GaAs for the design of MM-wave IMPATTs

A very staightforward method has been developed to apply space-charge resistance measurements for determining the high-field drift velocity of electrons in GaAs. The breakdown voltages of the single-drift flat-profile IMPATT diodes used in these measurements justify the validity of well known ionization rates for still higher electric fields.     

ATR-FTIR experiments with chlorosilanes

OH groups on the surface of semiconductors (SC) such as Si, Ge, TiO₂, SnO₂ react with Cl-Si groups to give stable SC-O-Si bonds. ATR-FTIR is applied to study the infrared spectra of adsorbed H₈Si₈O₁₂ on ZnSe and Cl₈Si₈O₁₂ which has reacted with the surface-OH group of Ge. A comparison is made with the spectra of the free molecules.     

Über die Synthese von N,N′-disubstituierten α-Iminophenyl-glyoxylsäurethionamiden und deren Reduktion mit Schwefelwasserstoff zu Phenylessigsäurethionamiden

Zusammenfassung Durch Umsetzung von ,-Dichloracetophenon mit überschüss. prim. Amin und Schwefel in äther. Lösung unter Zusatz von K₂CO₃ (Reaktionszeit 140 Stdn., Reaktionstemp. max. 20°) können N,N-disubstituierte -Iminophenylglyoxylsäurethionamide (1–3) in guten Ausbeuten synthetisiert werden.-Iminoglyoxylsäurethionamide (4–6), die am Imin- bzw. Aminstickstoff auch unterschiedlich substituiert sein können (4, 6), erhält man aus den entsprechenden Phenylglyoxylsäurethionamiden durch Umsetzung mit überschüss. primären Aminen.Die -Iminophenylglyoxylsäurethionamide können bereits bei Raumtemp. glatt durch H₂S zu den entsprechenden Phenylessigsäurethionamiden reduziert werden.

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Synthesis of N,N-disubstituted -iminophenyl-thioglyoxylic amides, and their reduction by means of H₂S to phenyl-thioacetic amides (Willgerodt—Kindler reaction, V.)

N,N-Disubstituted -iminophenylthioglyoxylamides (1–3) can be synthesized in good yields by the reaction of ,-dichloroacetophenone with excess primary amine and sulphur in eth. solution in the presence of potassium carbonate (reaction period 140 hours, reaction temperature max. 20°C).-Iminothioglyoxylamides (4–6), which may be differently substituted at the imine and amine nitrogen atoms (4, 6), may be obtained from the corresponding phenylthioglyoxylamides by reaction with an excess of primary amines.The -iminophenylthioglyoxylamides can be reduced smoothly at room temperature by hydrogen sulphide to the corresponding phenylthioacetamides.

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4. Mitt.:F. Asinger, A. Saus undA. Mayer, Mh. Chem.98, 825 (1967).

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Vgl. auchF. Asinger undH. Offermanns, Angew. Chem.79, 953 (1967).