[3+2]-cycloreactions of 1,2-diacylcyclopropenes with ynamines. Aminofurane- versus aminocyclopentadiene-formation

Electron deficient 1,2-diacylcyclopropenes represent synthetic equivalent for both acylcarbenes and vinylcarbenes; in their cycloreaction with ynamines aminofuranes and/or aminocyclopentadienes are formed.     

Evaluation of digestion procedures for the determination of iron and zinc in biscuits by flame atomic absorption spectrometry

An evaluation is made of different digestion methods for the determination of iron and zinc in biscuits prior to flame atomic absorption analysis. For the initial studies, microwave digestion was enough (using hydrogen chloride and nitric acid 3:1, v/v, at 180 °C and 600 W) to provide comparable accuracy, precision, digestion time and non-critical handling of reagents to dry-ashing and wet digestion (using different acid mixtures) and also to a simple acid treatment at room temperature. Although, after a simple microwave digestion, the spiked recoveries were found around 96–102%, to reduce the digestion time and for simplicity we worked on wet acid treatments. The results showed that acid-only treatment is not enough to digest the samples without adding ethanol, which was found necessary to digest organic residue at room temperature. The method was validated by comparison of the data found for commercial biscuit samples through using the proposed procedure and the AOAC official reference spectrophotometric method. Fe concentration in the different biscuits (such as petit beurre, baby biscuits, etc.) ranged from 1.21 to 15.96 mg/100 g while Zn concentration ranged from 0.58 to 2.50 mg/100 g depending on biscuit type. The highest concentration of Fe was in baby biscuits and these biscuits were about thirteen times richer in Fe than petit beurre biscuits.     

Short and flexible route to 3,4-diarylpyrrole marine alkaloids: syntheses of permethyl storniamide A, ningalin B, and lamellarin G trimethyl ether

A highly efficient route to 3,4-diarylpyrrole marine alkaloids has been developed using Hinsberg-type pyrrole synthesis and palladium-catalyzed Suzuki cross-coupling of the 3,4-dihydroxypyrrole bis-triflate derivatives as key reactions. Based on this approach, formal syntheses of permethyl storniamide A and ningalin B, and a total synthesis of lamellarin G trimethyl ether have been achieved.     

Zur Konjugation in makrocyclischen Bindungssystemen [1] XX. Charakterordnung,magnetische Suszeptibilitäten und chemische Verschiebungen von Corannulenen

Zusammenfassung Mit Hilfe von Berechnungen der Polansky-Charakterordnungen, der magnetischen Suszeptibilitäten und der chemischen Verschiebungen (¹H-NMR) im Rahmen der HMO-Theorie wird gezeigt, daß Corannulene nicht als makrocyclische Annulensysteme aufgefaßt werden können.

---

Conjugation in macrocyclic bonding systems XX. Order of character, magnetic susceptibility and chemical shifts of corannulenes

By means of calculations of the Polansky character order, ring current contributions to the magnetic susceptibilities and to the chemical shift in the Hückel approximation, it is shown, that corannulenes cannot be treated as macrocyclic annulenes.

---

Résumé Des calculs des caractères annulènoides, des contributions du courant cyclique à la susceptibilité magnétique et aux déplacements chimiques dans la méthode de HMO montrent, que les corannulènes ne peuvent pas considérer comme des annulènes macrocycliques.

---

---

Teilweise vorgetragen auf dem VII. Symposium für Theoretische Chemie vom 29. 3. bis 2. 4. 1971 in Göttingen.

---

Wir danken den Herren Prof. O. E. Polansky und Prof. G. Derflinger für hilfreiche Diskussionen, der Deutschen Forschungsgemeinschaft für die Unterstützung dieser Arbeit und dem Rechenzentrum der Universität Heidelberg für die Gewährung von Rechenzeit auf der IBM 360/44.