Spontaneous resolution and crystal structure of (2S)-2-(3-nitro-phen-yl)-3-phenyl-2,3,5,6-tetra-hydro-4H-1,3-thia-zin-4-one; crystal structure of rac-2-(4-nitro-phen-yl)-3-phenyl-2,3,5,6-tetra-hydro-4H-1,3-thia-zin-4-one.

Abstract

The crystal structures of isomeric rac-2-(4-nitro-phen-yl)-3-phenyl-2,3,5,6-tetra-hydro-4H-1,3-thia-zin-4-one (C16H14N2O3S) (1) and (2S)-2-(3-nitro-phen-yl)-3-phenyl-2,3,5,6-tetra-hydro-4H-1,3-thia-zin-4-one (C16H14N2O3S) (2) are reported here. While 1 crystallizes in a centrosymmetric space group, the crystal of 2 chosen for data collection has mol-ecules only with (2S) chirality. This is the result of spontaneous resolution during crystallization, as the synthesis produces a racemic mixture. A crystal with (2R) mol-ecules was also found in the same crystallization vial (structure factors available). The six-membered thia-zine ring in both 1 and 2 displays an envelope conformation with the S atom forming the flap. The aryl rings in both structures adopt an approximate V shape with angles between their planes of 46.97 (14)° in 1 and 58.37 (10)° in 2. In both structures, the mol-ecules form layers in the ab plane. Within such a layer in 1, one of the O atoms of the nitro-phenyl group accepts a C-H⋯O hydrogen bond from the CH group at position 5 of the thia-zine ring of a mol-ecule of opposite chirality, forming chains along the a-axis direction. Each of the thia-zine rings also participate in C-H⋯O bonds with the same carbon atom as above, resulting in chains along the b-axis direction, albeit of monochiral type. Adjacent layers are consolidated along the c-axis direction by pairs of parallel hydrogen bonds (C-H⋯O type) between the nitro-phenyl groups of enanti-omers. In 2, the two C-H⋯O hydrogen bonds contribute to chain formation along the b-axis direction. Weak edge-to-face inter-actions between the aryl groups of neighbouring mol-ecules in 1, and C-H⋯π inter-actions between a thia-zine ring CH group and a phenyl group of a neighboring mol-ecule in 2 are also observed.