The CON−H^…+NH₂ Blue-Shifting H-Bond Stabilizing Effect on Z Secondary Amides and Cyclic System Conformational Rearrangement through an Alkylamine-Chain Migration Pathway

Scheme 1

Protonation reactions of secondary (thio)amides described in the literature of the subject as the E isomers (1–3) and cyclic thioamides (4). Most of the published works on the activation of molecules in mixed systems containing the key structural elements required for H-binding such as the planar O-C-N groups (imidic acid skeleton) marked in red color, follow the above line. The interaction has thereby been used as a driving force for the desired geometrical selectivity in synthesis, accelerating the reaction towards one stereoisomer.