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 enanti-omerically pure title compound, C18H18N2O3S, comprises two independent mol-ecules (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 mol-ecules. The O atom on the S atom of the ring is pseudo-axial on the thia-zine ring and trans to both a phenyl group substituent and the acetamide group in each case. The two benzene rings in each mol-ecule are almost orthogonal to each other, with inter-planar dihedral angles of 83.79 (17) and 86.95 (16)°. The acetamide group is pseudo-equatorial and a phenyl ring is pseudo-axial on the thia-zine ring. Both mol-ecules show a weak intra-molecular C-H⋯O inter-action between H-atom donors of one of the phenyl rings and the acetamide group. In the crystal, an inter-molecular N-H⋯O(thia-zine) hydrogen bond links B mol-ecules along the 21 (b) screw axis and, in addition, an N-H⋯O(acetamide) hydrogen bond links A and B mol-ecules across a. A two-dimensional layered structure lying parallel to (001) is generated, also involving weak inter-molecular C-H⋯O inter-actions.