Protonation of captodative trifluoromethylated aminoalkenes and isomerization of their salts. An ab initio study

A study of the regioselectivity of protonation of captodative trifluoromethylated enamines was carried out using MP2/6-311+G(d,p) calculations and the natural bond orbital analysis. The central issue of this research concerns the influence of the electron-withdrawing group, which is not capable of the p,p-conjugation, on the properties of captodative enamines and their salts. The presence of CF3 group in such type of enamines levels the energy of their N-protonated and C-protonated forms. The transition states were found for both intramolecular and intermolecular processes of the proton transfer. The more possible mechanism of the isomerization of enammonium and iminium cations includes the proton transfer from N-protonated form to olefinic carbon atom of the starting enamine. The transition state energies, which correspond to intermolecular process, are relatively low (1113kcal mol1) in contrast to the intramolecular pathway (6469kcal mol1). Copyright (C) 2011 John Wiley & Sons, Ltd.