Fe3O4@MCM-41-SO3H@[HMIm][HSO4]: An effective magnetically separable nanocatalyst for the synthesis of novel spiro[benzoxanthene-indoline]diones

1-Methylimidazolium hydrogen sulfate was supported on Fe3O4@MCM-41-SO3H magnetic nanoparticles and was used for synthesis of novel spiro[benzo[a]xanthene-12,3′-indoline]-2′,11(8H)-diones and spiro[benzo[c]xanthene-7,3′-indoline]-2′,8(9H)-diones.230