Magnetically separable Fe3O4-SO3H nanoparticles as an efficient solid acid support for the facile synthesis of two types of spiroindole fused dihydropyridine derivatives under solvent free conditions

Magnetically separable Fe3O4-SO3H nanoparticles are found to act as an efficient solid supported acid catalyst for the facile synthesis of two types of spiroindole fused dihydropyridine derivatives such as spiro[indolo-3,10'-indeno[1,2-b]quinolin]-2,4,11'-triones and indenoquinoline-spirooxindoles under solvent-free conditions. Depending upon the nature of N-substitutions of the starting isatins (N-H or N-R/Ar) two different types of products are formed through three component one-pot condensation reactions. Operational simplicity, reduced reaction time, lower reaction temperature, elimination of solvents, high yields of the products, easy separation of Fe3O4-SO3H nanoparticles by means of an external magnetic bar and recyclability of Fe3O4-SO3H nanoparticles make the present method economical, green and sustainable.