Total synthesis of angucyclines .5. Synthesis of (+-)-rubiginone B2 by intra-molecular nucleophilic displacement of an anthraquinone precursor

Intramolecular nucleophilic displacement reaction of the ketoester 2 yields the angularly condensed system 7. Its conversion to the racemic angucycline antibiotic rubiginone B-2 (1a) is achieved by ethoxydecarbonylation to 8, deoxygenation via the thioketal 9 and photooxygenation.