Linear-conjugated enynones,1,5-diarylpent-4-en-2-yn-1-ones [Ar²−CH=CH−C≡C−C(=O)Ar¹], have been cyclized into 2,6-diaryl-2,3-dihydropyran-4-ones in triflic acid TfOH (CF₃SO₃H). Reactions of these enynones with arenes Ar³H in TfOH have afforded, at first stage, products of hydroarylation of the acetylene bond, 1,3,5-triarylpent-2,4-dien-1-ones [Ar²−CH=CH−C(Ar³)=CH−C(=O)Ar¹], which have been further cyclized into alkylidene indanes. Plausible reaction mechanisms have been proposed. According to quantum chemical calculations by DFT method, initial key reactive intermediates are vinyl type dications [Ar²−CH=CH−C⁺=CH−C(=O⁺H)Ar¹], generated under the protonation of carbonyl oxygen and acetylene bond of starting enynones in TfOH.