SYNTHESIS OF N-ACYLIMINIUM SALTS BY REACTION OF NITRILIUM SALTS WITH KETONES

A new method for the preparation of N-acyliminium salts 3a-ab by react ion of nitrilium salts 1 with non-enolizable alkyl and aryl ketones 2 is described. Ketones without electron-releasing substituents react on ly with N-arylnitrilium salts 1. An X-ray structural analysis was carr ied out for the N-acyliminium salt 3j. From variable temperature NMR s pectroscopy intramolecular conformational changes (essentially rotatio n around the iminium C=N double bond, coupled to rotation about the am ide C-N single bond) of few compounds 3 were determined. The observed barriers to hindered rotation are compared with barriers calculated by the AM1 method.