Regiospecific synthesis of benzo[b]fluorenones via ring contraction by benzil-benzilic acid rearrangement of benz[a]anthracene-5,6-diones

A regiospecific route to benzo[b]fluorenones is described. The synthesis is based upon a one-pot, regiospecific benzannulation of 1,4-dipolar synthons with naphthoquinone monoketal and ring contraction of the generated benz[a]anthracene-5,6-diones through benzil-benzilic acid rearrangement.