Protonation of 3-Arylpropynoic Acid Derivatives in Superacids |
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Authors: | S Walspurger A V Vasil'ev J Sommer P Pale P Yu Savechenkov A P Rudenko |
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Institution: | (1) Universite L. Pasteur, rue B. Pascal 4, Strasbourg, 67000, France;(2) St. Petersburg Academy of Forestry Engineering, Institutskii per. 5, St. Petersburg, 194021, Russia |
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Abstract: | 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. |
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