10-(3′-Nitro-4′-pyridyl)-1,8-diazaphenothiazine as the double Smiles rearrangement product

The modification of the phenothiazine structure via the substitution of the benzene ring with the pyridine ring may proceed through the Ullmann cyclization or the Smiles rearrangement of the appropriate sulfide followed by cyclization. Reaction of dipyridyl sulfide (4) with 4-chloro-3-nitropyridine (5) in DMF can lead to one of the isomeric nitropyridyldiazaphenothiazines (7, 9 or 10). Two-dimensional 1H NMR experiments (COSY and ROESY) and a single crystal X-ray diffraction study were used to reveal the right product structure 10, being the result of an uncommon reaction mechanism involving the double Smiles rearrangement of the S–N type. The tricyclic diazaphenothiazine system is not planar, folded along the S–N axis with the butterfly angle of 149.38(7)° between two pyridine rings. The central thiazine ring is in boat conformation with the nitropyridyl substituent located in equatorial position with the S5⋯N10–C11 angle of 162.3(2)°. The pyridyl substituent plane bisects the tricyclic ring system showing the dihedral angle between this plane and the C4a/C5a/C9a/C10a plane of 70.7(7)°. The nitro group is located intra the dipyridothiazine system and is tilted from the pyridine ring by 30.4(2)°.