A series of 11 novel 3‐aryl‐2‐phenyl‐2,3‐dihydro‐4H‐1,3‐benzothiazin‐4‐ones was prepared at room temperature by T3P‐mediated cyclization of N‐aryl‐C‐phenyl imines with thiosalicylic acid. This provides simple and ready access to N‐aryl compounds in this family, which have been generally difficult to prepare.

In the racemic title compound, C 20 H 15 NO 2 S, the planes of the two phenyl substituents form dihedral angles of 48.97 (15) and 69.26 (15) with that of the fused benzene ring of the parent benzothiazine ring, while the heterocyclic thiazine ring exhibits a screw-boat pucker. The O atom on the S atom of the ring is pseudo-axial on the thiazine ring and trans to the 2-phenyl group. In the crystal, molecules are arranged in layers in the ac plane, the layers being linked across b through intermolecular C-HÁ Á ÁO hydrogen-bonding interactions.

In the adduct resulting from the reaction of 2,3-diphenyl-3,4,5,6-tetra­hydro-2H-1,3-thia­zin-4-one with tri­phenyl­tin chloride, the three rings of the tri­phenyl­tin group are involved in intra­molecular inter­actions of different types, and all the phenyl rings participate in inter­molecular π–π inter­actions.