We developed Hg(OTf)2-catalyzed Friedel–Crafts-like cycloisomerization of 7-arylhepta-1,3-dienes to give propenyl-substituted tetrahydronaphthalenes in excellent catalytic turnover under very mild conditions. 1,3-Dienyl sulfonamides and 1,3-dienyl alcohols were also efficiently cyclized to afford heterocyclic compounds.