Gravar-mail: The crystal structures of 6′-(4-chloro­phen­yl)- and 6′-(4-meth­oxy­phen­yl)-6a′-nitro-6a′,6b′,7′,9′,10′,12a′-hexa­hydro-2H,6′H,8′H-spiro­[ace­naphthyl­ene-1,12′-chromeno[3,4-a]indolizin]-2-one