Synthesis of Divergent Benzo[b]fluorenones through Cycloaromatization Reactions of 1,5-Enynols and 1,5-Diynols

A facile and efficient synthesis of divergent benzo­[b]­fluorenones is described through the use of dichlorobenzoquinone-promoted oxidative cycloaromatization reactions of acyclic 1,5-enynols and 1,5-diynols. The success of these cascade reactions depends on the chemoselectivity of the initial Meyer–Schuster rearrangement to produce allenol intermediate, which is followed by regioselective Schmittel cyclization and the subsequent Friedal–Crafts alkylation or radical attack at the terminal Ar moiety. Only an oxidant and a solvent were required in the reaction, thus delivering a small library of the expected polycarbocyclic products with excellent functional group tolerance under metal-free conditions. The absorption and photoluminescence properties of the selected benzo­[b] fluorenones were also investigated. The results indicated that the compound (2h) which contained an electron-donating 4-OMe group at the phenyl moiety displayed deep green color emission (491 nm).