Combined directed ortho metalation—intramolecular Friedel–Crafts connections. Regiospecific route to 1-substituted fluoren-9-ones

ortho-Substituted-2-biphenyl carboxylic acids of the type 3a–j were prepared by the tandem metalation sequence from 2-biphenyl carboxylic acid 1 with sec-butyllithium in THF at −78°C followed by quenching with electrophiles. The carboxylic acids 3a–f were converted into 1-substituted fluorenones 4a–f upon treatment with methanesulfonic acid.