Electrochemical reductions of 2,2,2-triclhoroethylideneacetophenones carried out in the presence of acetic acid lead to 1-aryl-4.4-dichlorobut-3-en-1-ones in near quantitative yields with total exclusion of 2,2-dichloroethylideneacetophenones isomers. The origin of the selectivity towards the formation of unconjugated beta, gamma-unsaturated ketones without competitive generation of alpha, beta-unsaturated isomers has been studied on the basis of chemical, voltammetric and HF and B3LYP density functional computational methods. It has been concluded that dienol intermediates are involved in the operating reaction mechanism but dienolate anions are not its precursors. The participation of acetic acid as a catalyst promoting the ketonization of dienols through C-alpha protonation with concomitant deprotonation of the hydroxyl group is proposed. (C) 2008 Elsevier Ltd. All rights reserved.