Formation of Benzo[b]fluorenes and the Benzo[a]fluorene Core of the Fluostatins by Cyclization of Diaryldiynones

[figure: see text] Thermal cyclization of 1-[2-(trimethylsilylethynyl)phenyl]-3-arylpropinones was expected to give benzo[b]fluorenones. However, benzo[a]-fluorenones were also formed as a result of a new rearrangement. These tetracycles possess the core structure of the fluostatins and isoprekinamycin.