Formation of 2-Imino Benzo[e]-1,3-oxazin-4-ones from Reactions of Salicylic Acids and Anilines with HATU: Mechanistic and Synthetic Studies

We describe a new 1-[Bis(dimethylamino)methylene]-1 H -1,2,3-triazolo[4,5- b ]pyridinium 3-oxide hexafluorophosphate (HATU)-mediated coupling reaction to produce 2-imino benzo[ e ]-1,3-oxazin-4-ones from salicylic acids and anilines. Mechanistic studies support a reaction pathway in which HATU mediates carbon transfer to the initially formed salicylanilides to form in succession reactive tetramethylisouronium and N -acyl(dimethyl)isouronium intermediates, which then undergo imine-iminium exchange to generate the desired oxazinones.