1-(4-Sulfonic Acid Butyl)-3-Methylimidazolium Polyoxo Metalate as a Novel Nano-Hybrid Catalyst for the One-Pot Synthesis of 4H-Pyran and Spiro Indoline Derivatives

Abstract

Organic-inorganic nanohybrid ionic liquid based on polyoxometalate [H2 [MIMBS]4 [P2W18O62].11H2O] (MIMB-P2W18) has been synthesized and characterized by elemental analysis technique, Fourier transform infrared (FT-IR), 1H, 13C, and 15P nuclear magnetic resonance (NMR), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The catalytic activity of this nanohybrid ionic liquid has been studied in multi-component reactions to generate pyran and spiro indoline derivatives. Tetrahydrobenzo[b]pyrans have been successfully synthesized by one-pot three-component condensation of aldehyde, malononitrile and dimedone (or cyclohexane-1,3-dione/3-methyl-2-pyrazoline-5-one) using MIMB-P2W18 as a heterogeneous nano-catalyst. Furthermore, a set of multi-substituted spiro[indoline-3,4׳-pyrano[2,3-c]pyrazole] has been synthesized from isatin, hydrazinehydrate/phenylhydrazine, ethyl acetoacetate and malononitrile/ethyl cyanoacetate in the presence of the same catalyst via one-pot four-component method at room temperature. These procedures have several advantages such as high yields of product, easy work-up procedure, short reaction time and stability, non-toxicity, cheapness and reusability of the catalyst.