Chemistry of the phenoxathiins and isosterically related heterocycles. XXIV . Synthesis of characterization by 13C-NMR spectroscopy of isomeric benzoxathiinopyridazinones: 1-Oxo-1,2-dihydro-2,3-diazaphenoxathiin and 4-Oxo-3,4-dihydro-diazaphenoxathiin. The first observation of a smiles rearrangement