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According to the 1H and 13C NMR data, 3-arylpropynoic acids and their esters XC6H n -C≡C-CO2R (R = H, Me, Et) having electron-withdrawing substituents in the benzene ring (X = NO2, CN, COMe, CO2Me) exist in HSO3F at −80 to 0°C as XC6H n -C≡C-C+(OH)OR ions. Derivatives with other substituents (X = H, F, Me, MeO) in HSO3F or CF3SO3H above −40°C undergo protonation at the acetylenic carbon atom neighboring to the acid group to give unstable vinyl-type XC6H n -C+=CH-CO2R cations which are then transformed into mixtures of stereoisomeric ( Z and E) fluorosulfonates or triflluoromethanesulfonates XC6H n -CY=CH-CO2R (Y = OSO2F, OSO2CF3), the E isomer prevailing. [ABSTRACT FROM AUTHOR]

Abstract: In superacids HSO3F and CF3SO3H, it has been found that 3-arylindenones are very stable and exist as a doubly protonated species. NMR showed protonation both at the oxygen of the carbonyl group and at the C2 carbon of the indenone system. 3-Arylindenones proved however very sensitive to heat and light. Their [2+2] photodimerization under daylight has been studied. [Copyright &y& Elsevier]

1,3-Diarylpropynones ArC=CCOAr' in superacids withH0 ranging from -20 to - 14 undergo protonation at the carbonyl oxygen atoms to give stable ArC=CC(O+H)Ar' ions or at the acetylenic C2 atom with formation of reactive ArC+=CHCOAr' species. The effects of the Ar and Ar' substituents and reaction conditions on the intramolecular cyclization of ArC+=CHCOAr' to 3-arylinden-1-ones are discussed. [ABSTRACT FROM AUTHOR]

Describes a new [2 + 2]-dimerization of 3-arylindenones Ia and Ib to syn,transadducts IIa and IIb, which occurs extremely readily on exposure to daylight. Determination of the structure of dimer IIb by X-ray analysis; Rationalization of the formation of adducts IIa and IIb in terms of general relations holding in photochemical cycloaddition of enones to alkenes.