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, C(20)H(16)N(2)O(3)S, (I), and C(21)H(18)N(2)O(3)S, (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[Image: see text]). 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.