Crystal structures of 6a,6b,7,11a-tetrahydro-6H,9H-spiro[chromeno[3′,4′:3,4]pyrrolo[1,2-c]thiazole-11,3′-indoline]-2′,6-dione and 5′-methyl-6a,6b,7,11a-tetrahydro-6H,9H-spiro[chromeno[3′,4′:3,4]pyrrolo[1,2-c]thiazole-11,3′-indoline]-2′,6-dione

The title compounds, C20H16N2O3S, (I), and C21H18N2O3S, (II), differ by the presence of a methyl group in position 5 on the 1H-indole-2-one ring of compound (II). The two compounds have a structural overlap r.m.s. deviation of 0.48 Å. There is a significant difference in the conformation of the thiazolidine ring: it has a twisted conformation on the fused N—C bond in (I), but an envelope conformation in compound (II) with the S atom as the flap. The planar pyrrolidine ring of the indole ring system is normal to the mean plane of the five-membered pyrrolidine ring of the pyrrolothiazole unit in both compounds, with dihedral angles of 88.71 (9) and 84.59 (8)°. The pyran rings in both structures have envelope conformations with the methylene C atom adjacent to the C=O group as the flap. In both compounds, there is a short intramolecular C—H...O contact present. In the crystal of (I), molecules are linked by C—H...O hydrogen bonds forming chains propagating along the b-axis direction. The chains are linked by N—H...π interactions, forming layers parallel to (10\overline{1}). In the crystal of (II), molecules are linked by pairs of N—H...O hydrogen bonds, forming inversion dimers which are linked by C—H...O hydrogen bonds to form a three-dimensional structure.