Crystal structure of ethyl 2′′, 3-dioxo-7′, 7a'-di­hydro-1′H, 3H, 3′H-di­spiro[benzo[b]thio­phene-2, 6′-pyrrolo­[1, 2-c]thia­zole-5′, 3′′-indoline]-7′-carboxyl­ate. (March 2015)