Diisobutylaluminum Hydride Promoted Cyclization of o‑(Trimethylsilylethynyl)styrenes to Indenes

The reaction of o-(trimethylsilylethynyl)­styrenes with diisobutylaluminum hydride (DIBAL-H) provides 2-trimethylsilyl-1H-indenes efficiently. The cyclization mechanism involves regioselective hydroalumination of the alkynyl moiety, geometrical isomerization of the alkenylaluminums formed, and intramolecular carboalumination. With substrates bearing a 2-(trimethylsilyl)­ethenyl group (R1 = Me3Si, R2 = R3 = H), bis-silylated benzofulvenes are obtained upon treatment of the reaction mixture with an excess amount of benzaldehyde.