Die Geburt einer Struktur: Zur 60. Wiederkehr der Aufstellung der Azulenformel durch Pfau und Plattner

Teil 2a)

Abstract

The historical way is described, how Pfau and Plattner arrived at the right formula of the azulenes. Starting from the ketone fraction of vetiver oil, they were able to separate from this fraction two sesquiterpenoid bicyclie ketones which they named α -and β-vetivone. Especially β-vetivone attracted their attention, since itself as well as reduced forms of it gave, on dehydrogenation at high temperature in the presence of sulfur, selenium or palladium on charcoal, a new type of azulene which they called vetivazulene. Dehydrogenation experiments with a new compound that had originally been synthesized by W. Hückel et al. and possessed an anellated five-seven ring system led also to blue azulenes. This observation together with a number of further results allowed Pfau and Plattner to assign the right structure also to vetiv- and guaiazulene. Degradation experiments with β-vetivone and reduced forms of it suggested to assume a corresponding hydroazulene skeleton also for β-vetivone. 30 years later, J.A. Marshall et al. showed that the structure of β-vetivone had to be changed into a spiro[4.5]decane ring system, showing the same symmetry properties as the originally proposed cis-fused hydroazulene system.