Computer-aided insight into the relative stability of enamines

Venerable aldol, Michael, and Mannich reactions have undergone a renaissance in the past fifteen years, as a consequence of the development of direct organocatalytic versions, mediated by chiral amines. Chiral enamines are key intermediates in these reactions. This review focuses on the formation of enamines from secondary amines and their relative thermodynamic stability, as well as on the reverse reactions (hydrolysis). Experimental results and predictions based on MO calculations are reviewed to show which enamine forms may predominate in the reaction medium and to compare several secondary amines as organocatalysts.1 Introduction2 Relative Stability of Enamines as Determined Experimentally3 Pyrrolidine Enamines4 Enamines of the Jorgensen-Hayashi Catalyst5 Proline Enamines6 Free Enthalpies and Polar Solvent Effects7 Comparison of Organocatalysts8 Summary and Outlook9 Appendix