Clerodane-3,4-oxides

The first total synthesis of the clerodane alkaloid solidago alcohol was achieved in the laboratory of H.-S. Liu, using a highly diastereoselective DIels-Alder cycloaddition as the key step. The installation of the 3-furyl side chain required the conversion of the bicyclic primary alkyl bromide to the corresponding aldehyde. This was accomplished by the modified Kornblum oxidation, which employed silver tetrafluoroborate to activate the substrate. 

To date more than 100 species from the large genus Baccharis have been investigated chemically. The most widespread compounds are clerodane diterpene derivatives, but labdane derivatives have also been isolated. Furthermore, typical acetylenic compounds, baccharis oxide, a unique triterpene, and derivatives of hydroxyacetophenone are present, although it is mainly other biologically active constituents, e.g. flavonoids, sesquiterpenes and essential oils that have been reported in the last years. The constituents of Baccharis species compiled from different sources are presented below. 

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