Determination of the electrophilic reactivities of 1,1,3-triarylallyl cations

Abstract

The 1,1,3-triphenylallyl cation and its p-methoxy and p-dimethylamino substituted derivatives have been generated in dichloromethane solution or as stable salts. Allylsilanes, allylstannanes, silylated enol ethers and ketene acetals, as well as enamines attack the sterically less hindered 3-position of the allyl cation as derived from the structures of the reaction products. Kinetic investigations of these reactions revealed that they follow the equation log k(20 °C) = s(N + E), which allows one to derive the electrophilicity parameters E of Ph₂CCH–CH⁺Ph (E = +0.98 ± 0.20), (p-MeOC₆H₄)₂CCH–CH⁺Ph (E = −2.67 ± 0.30), (p-Me₂NC₆H₄)₂CCH–CH⁺Ph (E = −8.97 ± 0.32) and (p-Me₂NC₆H₄)₂CCH–CH⁺(p-Me₂NC₆H₄) (E = −9.84 ± 0.21).