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

Abstract

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.