Which Factors Control the Nucleophilic Reactivities of Enamines?

Changes in rate constants, equivalent to changes in Gibbs energies of activation Delta G(double dagger), are commonly referred to as kinetic effects and differentiated from thermodynamic effects (Delta,G degrees). Often, little attention is paid to the fact that structural effects on Delta,G(double dagger) are composed of a thermodynamic (Delta G degrees) and a truly kinetic (intrinsic) component (Delta G(0)(double dagger)), as expressed by the Marcus equation. Rate and equilibrium constants have been determined for a number of reactions of enamines with benzhydrylium ions (Aryl(2)CH(+)), which has allowed the determination of Marcus intrinsic barriers and a differentiated analysis of structure-reactivity relationships. To our knowledge, this is the first report in which the Lewis basicity of a pi(cc) bond towards carbon-centered Lewis acids (for example, carbenium ions) has quantitatively been determined. The synthesis, structures, and properties of deoxybenzoin-derived enamines ArCH=C(Ph)NR2, which have been designed as reference nucleophiles for the future quantification of electrophilic reactivities, are explicitly described.