Superacidic trifluoromethanesulfonic acid (triflic acid, TFSA) catalyzes the alkylation of benzene with various cyclic ethers. The characteristic products formed in the reaction of highly reactive oxiranes (methyloxirane, styrene oxide, and cyclohexene oxide) are phenyl-substituted compounds formed as a result of Friedel-Crafts-type mono- and dialkylation. Oxetanes (2-isopropyloxetane) and oxolanes (tetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,2,5,5-tetramethyltetrahydrofuran), in turn, undergo electrophilic cyclialkylative ring closure (cyclialkylation) to form mainly bicyclic compounds (tetralin, dihydronaphthalene, and naphthalene derivatives). In the majority of cases, alkylated products can be isolated in good to reasonable yields. Reactivity of cyclic ethers, product formation and product distributions are interpreted by taking into account ring strain, acidity of reaction mixtures and stability of carbocationic intermediates.