Crystal structure of (1S,2S,5R)-5-acetylamino-4- oxo-2,3-diphenyl-1,3-thiazinan-1-ium-1-olate

The asymmetric unit of the enantiomerically pure title compound, C₁₈H₁₈N₂O₃S, comprises two independent molecules (A and B) having almost identical conformations. When overlayed, the alignment-r.m.s. deviation value is 0.30 Å . The six-membered heterocycle has a twisted half-chair conformation in both molecules. The O atom on the S atom of the ring is pseudo-axial on the thiazine ring and trans to both a phenyl group substituent and the acetamide group in each case. The two benzene rings in each molecule are almost orthogonal to each other, with interplanar dihedral angles of 83.79 (17) and 86.95 (16)^s. The acetamide group is pseudo-equatorial and a phenyl ring is pseudo-axial on the thiazine ring. Both molecules show a weak intramolecular C-H...O interaction between H-atom donors of one of the phenyl rings and the acetamide group. In the crystal, an intermolecular N-H...O(thiazine) hydrogen bond links B molecules along the 21 (b) screw axis and, in addition, an N-H...O(acetamide) hydrogen bond links A and B molecules across a. A two-dimensional layered structure lying parallel to (001) is generated, also involving weak intermolecular C-H...O interactions.