Synthesis of the benz[a]anthraquinone core of angucyclinone antibiotics

reaction: see text] A general method for the synthesis of benza]anthraquinones is reported. The key step is a catalytic cobalt-mediated 2+2+2]-cycloaddition of a triyne, which affords an angularly substituted tetracycle. Oxidation of this core gives the typical structure of angucyclinone antibiotics.