Which Factors Control the Nucleophilic Reactivities of Enamines?
Chemistry A European Journal, 2018, 24, 5901-5910
Changes in rate constants, equivalent to changes in Gibbs energies of activation ΔG≠, are commonly referred to as kinetic effects and differentiated from thermodynamic effects (ΔrG°). Often, little attention is paid to the fact that structural effects on ΔG≠ are composed of a thermodynamic (ΔrG°) and a truly kinetic (intrinsic) component (ΔG0≠), as expressed by the Marcus equation. Rate and equilibrium constants have been determined for a number of reactions of enamines with benzhydrylium ions (Aryl2CH+), 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 πCC 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.