The allobetulin dehydration product, α-apoallobetulin, has been shown to be represented by structure IV. Initial support for this assignment was obtained by oxidizing α-apoallobetulin to a diketone (VII). Direct oxidation of α-apoallobetulin to diketone VII was unexpectedly achieved employing a modified osmium tetroxide-pyridine procedure. The same oxidation product was prepared by ozonization of α-apoallobetulin and by lead tetraacetate oxidation of its glycol derivative (VI). Substantial evidence favoring the proposed endocvclic olefin (IV) formulation was provided by the facile isomerization of δ-apoallobetulin (III) to α-apoallobetulin. The ketone (VIII) obtained following ozonization of δ-aponllohetulin was assigned an A/B cis-configuration on the basis of optical rotatory dispersion measurements.
ASJC Scopus subject areas
- Organic Chemistry