Nuclear magnetic resonance investigations of iminium ion intermediates. Part 9. Multinuclear study of the reaction between Lewis acids and vinylogous amides

Abstract

When treated with Lewis acids the vinylogous amides have analogous synthetic behaviour to that of amides. The structure and the electronic properties of the intermediate complexes formed in the course of the reactions between COCl₂ or POCl₃ and enaminoaldehydes, enaminoketones, or p-dimethylaminobenzaldehyde have been investigated. These complexes are identified and the mechanism is compared with that of the Vilsmeier reaction. The stereochemistry of the products is elucidated and examined in the light of the possible exchange processes. Electron delocalization in both the neutral compounds and cations of the type (CH₃)₂N C C C A are discussed on the basis of nitrogen chemical shifts and rotational barriers.