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

The 1,1,-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 degreesC) = s(N + E), which allows one to derive the electrophilicity parameters E of Ph2C=CH-CH+Ph (E = +0.98 +/- 0.20), (p-MeOC6H4)(2)C=CH-CH+Ph (E = -2.67 +/- 0.30), (p-Me2NC6H4)(2)C=CH- CH+Ph (E = -8.97 +/- 0.32) and (p-Me2NC6H4)(2) C=CH-CH+ (p-Me2NC6H4) (E = -9.84 +/- 0.21).