Molecular structure and 13 C chemical shift assignments of 10‐(2′‐pyridyl)pyrido[3,2‐ b ][1,4]benzothiazine using 10‐phenylpyrido[3,2‐ b ][1,4]benzothiazine as the model compound

The crystal structure of 10‐(2′‐pyridyl)pyrido[3,2‐b][1,4]benzothiazine, 6 , shows that orientation of the 10‐pyridyl ring is in the plane bisecting the pyridobenzothiazine ring. This orientation is in contrast to that of 10‐(2′‐pyridyl)phenothiazine, 11 , in which the heterocyclic ring is perpendicular to the plane bisecting the phenothiazine nucleus. X‐ray data also indicate that the resonance interaction between the lone pair of electrons of NSUB10 in 6 with either the pyridine protons of the tricylcic ring or the 10‐(2′‐pyridyl) ring is not significant. The folding angle of 166.1° in 6 is the largest observed for the pyridobenzothiazine ring. The nmr spectral assignments of the titled compound, 6 , was accomplished using the structurally similar, 10‐phenylpyrido[3,2‐b][1,4]benzothiazine, 9 , as the model compound. 10‐(2′‐Pyridyl)phenothiazine, 11 , was shown to be an inadequate model for such assigments.