Reactions of 5,5,5-trichloropent-3-en-2-one Cl₃CCH=CHC(=O)Me with arenes in Brønsted superacid CF₃SO₃H 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 Cl₃CCH=CHC(=OH⁺)Me, has been studied experimentally by NMR in CF₃SO₃H and theoretically by DFT calculations. The reaction proceeds through initial hydroarylation of the carbon-carbon double bond of starting CCl₃-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 CF₃SO₃H acts as a 1,3-bi-centered electrophile.