Acetylene carbonyl compounds ArC CCOR (R = H, Me, Ph) form vinyl cations ArC+=CHCOR or ArC+=CHC(OH)R+ at the protonation in Bronsted and conjugate Bronsted-Lewis superacids (protic superacids: HSO3F, CF3SO3H, HSO3F-SbF5, CF3SO3H-SbF5, HAlBr4) with a wide range of acidity (H-o similar to -11 to -22). The vinyl cations react with arenes Ar' H with the formation of alkenylation products ArAr' C=CHCOR. On the contrary to protic superacids Lewis acids (AlBr3, AlCl3) activate additionally electrophilic center at carbonyl carbon of the compounds ArC CCOR that leads to the formation of substituted indenes in their reactions with arenes. (c) 2007 Elsevier B.V. All rights reserved.