Vinyl type carbocations ArC⁺=CHX [X = CO₂H, CO ₂Alk, C≡N, P(O)(OAlk)₂] generated from alkyl 3-arylpropynoates and related compounds in fluorosulfonic acid at -75 to -20°C react with various benzene derivatives, following the mechanism of electrophilic substitution of hydrogen. A new procedure for the synthesis of alkyl 3,3-diarylpropenoates having various substituents in the aryl fragments has been developed on the basis of protonation of the triple bond in alkyl 3-arylpropynoates.