5,5,5-Trichloropent-3-en-one as a Precursor of 1,3-Bi-centered Electrophile in Reactions with Arenes in Brønsted Superacid CF 3 SO 3 H. Synthesis of 3-Methyl-1-trichloromethylindenes.

Reactions of 5,5,5-trichloropent-3-en-2-one Cl 3 CCH=CHC(=O)Me with arenes in Brønsted superacid CF 3 SO 3 H at room temperature for 2 h-5 days afford 3-methyl-1-trichloromethylindenes, a novel class of indene derivatives. The key reactive intermediate, O -protonated form of starting compound Cl 3 CCH=CHC(=OH + )Me, has been studied experimentally by NMR in CF 3 SO 3 H and theoretically by DFT calculations. The reaction proceeds through initial hydroarylation of the carbon-carbon double bond of starting CCl 3 -enone, followed by cyclization onto the O -protonated carbonyl group, leading to target indenes. In general, 5,5,5-trichloropent-3-en-2-one in CF 3 SO 3 H acts as a 1,3-bi-centered electrophile.