Formation of 2‑Imino Benzo[<i>e</i>]‑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]-1H-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.