A Simple and One-pot Synthesis of Tetrahydrobenzo[b]pyrans and Spirooxindoles Catalyzed by H-Fe3O4@DA-SO3H as an Efficient, Light and Reusable Nanocatalyst

Aim and Objective: One of the principles of green chemistry is using inexpensive reagents and catalysts to design green route for synthesis of organic compounds. Recently magnetic nanoparticles have provided a considerable merits. In this study, hollow Fe3O4@Dopamine-SO3H has been successfully applied for the green synthesis of tetrahydrobenzo[b]pyrans and spirooxindoles via one-pot multi-component reaction. Materials and Methods: Chemical reagents were purchased from Merck and Aldrich. Melting points were determined using an Electrothermal 9100. Fourier transform infrared and NMR spectra were recorded with a Shimadzu 8400 spectrometer and Bruker spectrometer, respectively. Results: The reaction between benzaldehyde, malononitrile and dimedone was selected as the model for synthesis of tetrahydrobenzo[b]pyran. The obtained results showed that the best amount of catalyst is 0.01 g and the reaction has occurred in solvent free condition at 70°C. The results showed that both electron-withdrawing and electron-donating substituents have an acceptable yield in the reaction. After that the scope of this method was evaluated in one-pot synthesis of spirooxindole derivatives through three-component reaction of isatin derivatives, malononitrile or ethyl cyanoacetate and 1,3-cycllic diketone. The optimum condition was 0.01 g catalyst using H2O under reflux condition. Then other derivatives produced in excellent yields during short reaction times. Conclusion: Tetrahydrobenzo[b]pyran and spirooxindole derivatives in the presence of this catalyst were synthesized. The ease of preparation and handling of the catalyst and operational simplicity are some of the main advantages of this work. In addition, the catalyst could be recycled and reused at least six times without notable reduction in its catalytic activity.