A Sustainable Synthesis of Functionalized Pyrrole Fused Coumarins under Solvent-Free Conditions Using Magnetic Nanocatalyst and a New Route to Polyaromatic Indolocoumarins
A general and environmentally benign one-pot method has been developed for the library synthesis of biologically important chromeno[4, 3-b]pyrrol-4(1H)-one derivatives. A three-component domino condensation of 4-aminocoumrins, arylglyoxal monohydrates and various nucleophilic substrates, such as, arylamines, malononitrile, ethyl cyanoacetate and cyanoacetamide produced functionalized chromeno[4, 3-b]pyrrol-4(1H)-ones in presence of magnetically separable Fe3O4@SiO2-SO3H nanoparticles as solid acid catalyst under solvent free conditions. Furthermore, a two-component condensation of 4-aminocoumrins and arylglyoxal monohydrates furnished a series of hydroxy functionalized chromeno[4, 3-b]pyrrol-4(1H)-ones under similar reaction conditions. The salient features of the present method are mild reaction conditions, reduced reaction time, elimination of hazardous solvents, good yield of the products, greater substrate scope and use of a magnetically separable and recyclable nanocatalyst. Moreover, it has been observed that a class of chromeno[4, 3-b]pyrrol-4(1H)-one derivatives can be easily converted to biologically important indolo[3, 2-c]coumarin derivatives in good yield through intramolecular thermal cyclization without using any catalyst.