Gravar-mail: Crystal structure of ethyl 5′′-fluoro-2′′,3-dioxo-6′,7′,8′,8a’-tetra­hydro-2′H,3H,5′H-di­spiro­[benzo[b]thio­phene-2,1′-indol­izine-3′,3′′-indoline]-2′-carboxyl­ate