On the selective electrogeneration of 1-aryl-4,4-dichlorobut-3-en-1-ones from 2,2,2-trichloroethylideneacetophenones: A combined experimental and HF and B3LYP computational study

Electrochemical reductions of 2,2,2-trichloroethylideneacetophenones 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 β,γ-unsaturated ketones without competitive generation of α,β-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- α protonation with concomitant deprotonation of the hydroxyl group is proposed.