Synthesis of the Benzo[b]fluorene Core of the Kinamycins by Arylalkyne–Allene and Arylalkyne–Alkyne Cycloadditions

Arylalkyne–allene and arylalkyne–alkyne cycloadditions yields benzo[ a ]fluorenones, which are related to the tetracyclic core of the kinamycins. In the arylalkyne–alkyne cycloadditions, we found a rearrangement that produces benzo[ a ]fluorenones, in addition to the expected benzo[ b ]fluorenones. This rearrangement could be suppressed in the presence of phenol, which allowed the synthesis of 4,9‐dimethoxy‐2‐methyl‐11 H ‐benzo[ b ]fluoren‐11‐one in excellent yield.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)