Diels–Alder reactions of 1,1,3-triarylallyl cations: determination of the free energy of concert

1,1,3-Triarylallyl cations react with 1,3-dienes to give Diels–Alder products in low to moderate yields. The observed second-order rate constants agree with those calculated for the stepwise processes by the correlation log k(20 °C) = s(N + E) [eqn. (1)] indicating the absence of a significant free energy of concert. Eqn. (1) can, therefore, also be employed for the prediction of absolute rate constants of Diels–Alder reactions of allyl cations.