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).