The syntheses and crystal structures of two thiazinone compounds, namely, rac-2,3-diphenyl-2,3,5,6-tetrahydro-4H-1,3-thiazine-1,1,4-trione, C16H15NO3S, in its racemic form, and N-[(2S,5R)-1,1,4-trioxo-2,3-diphenyl-1,3-thiazinan-5-yl]acetamide, C18H18N2O4S, in an enantiopure form, are reported. The thiazine rings in the two structures differ in their puckering, as a half-chair in the first and a boat pucker in the second. The extended structures for both compounds have only C—H...O-type interactions between symmetry-related molecules, and exhibit no π–π stacking interactions in spite of each having two phenyl rings.