Lactam acetals and acid amides. 31. Synthesis,protonation, and basicities of some heterocyclic enamino ketones

The protonation of cyclic enamino ketones of the pyrrolidine, piperidine, and hexahydroazepine series, as well as their noncyclic analogs, was studied by PMR spectroscopy. It is shown that the presence of a CH₂ or CH₃ group in the “enamine” position leads to C protonation (in CF₃COOH). In the case of enamino ketones that do not contain substituents in the “enamine” α position N-and O-protonated forms are observed in CF₃COOH. The measured pK_a values (in 10% alcohol) and the ΔpK_a values (in nitromethane) of the enamino ketones show that the compounds for which C protonation is characteristic are two to three orders of magnitude more basic than in the case of compounds that do not contain substituents in the “enamine” α position; this is explained by the different character of protonation. See 1] for communication 30. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 344–348, March, 1980