Chemistry of 1,3-diarylpropynones in superacids

Abstract

In superacids with H₀ = −14 to −20, it has been found that 1,3-diarylpropynones ArCCCOAr′ are either protonated on oxygen of carbonyl groups with the formation of stable ions ArCCC(O⁺H)Ar′ or undergo further transformations when the highly conjugated system is electron-rich enough. In the latter case, 3-arylindenones are produced very rapidly and with high efficiency (up to 95% yield in less than 30 min). The influence of the substituents Ar, Ar′ and of the reaction conditions on the behavior of 1,3-diarylpropynones and on the intramolecular cyclisation have been studied. From the collected data, a mechanism has been proposed involving vinyl cations ArC⁺=CHCOAr′ and/or dications ArC⁺=CHC(O⁺H)Ar′.