Intramolecular Arylative Ring Opening of Donor-Acceptor Cyclopropanes in the Presence of Triflic Acid: Synthesis of 9H-Fluorenes and 9,10-Dihydrophenanthrenes

A unique intramolecular arylative ring opening of 2-biaryl substituted donor-acceptor cyclopropanes in the presence of triflic acid was found, furnishing 9H-fluorenes and 9,10-dihydrophenanthrenes. Chemoselectivity between both products is achieved by modification of the solvent, temperature, and amount of triflic acid. Representative large-scale experiments were also carried out successfully with good outcomes.