Nano-Fe3O4@SiO2 coated poly acrylic acid as an efficient catalyst for the synthesis of tetrahydrobenzo[b]pyran and 3,4-dihydropyrano[c]chromene derivatives

Recently preparation and the use of nanoparticles (NPs) in organicsynthesis has become a subject of intense investigation. In particular, magnetic nanoparticles (MNPs) which offer advantages inclean and sustainable chemistry and also they can be nontoxic, readilyaccessible, and retrievable. Additionally, the activity and selectivity of magnetic nanocatalysts can be manipulated by its surfacemodification [1].Among these support materials, magnetic nanoparticles are verypopular when used for immobilization of active homogeneouscatalyst because their magnetic response causes simpleseparation of catalyst by using an external magnet. Howevermagnetic nanoparticles always tend to undergo agglomerationbecause of the magnetic dipole−dipole attractions betweenparticles; it was reported that formation of a passive coating ofinert materials such as polymers on the surfaces of iron oxidenanoparticles could help to prevent their aggregation insolvents and improve their chemical stability [2]. Herein we report a magnetically supported acidic polymeric on Fe3O4@SiO2 nanoparticles (Fe3O4@ SiO2-Guanidine-poly acrylic acid) was synthesized and evaluated as a recoverable catalyst for the One-Pot synthesis of tetrahydrobenzo[b]pyran and 3,4- dihydropyrano[c]chromene derivatives in high to excellent yield under ethanol/H2O solvent conditions.