Chemistry of 1,3-diarylpropynones in superacids.

In superacids with H0=-14 to -20, it has been found that 1,3-diarylpropynones ArC triple bond CCOAr' are either protonated on oxygen of carbonyl groups with the formation of stable ions ArC triple bond CC(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'.