Abstract
A novel base-metal multifunctional nanomagnetic catalyst is prepared by the immobilization of tungstate anions onto γ-Fe2O3 supported with imidazolium moieties. The (γ-Fe2O3-Im-Py)2WO4 was fully characterized using FT-IR, XPS, TEM, FESEM, ICP, TGA, VSM and XRD and used as a multifunctional heterogeneous catalyst for the synthesis of 2-amino-3-cyano-4H-chromenes via a multicomponent tandem oxidation process starting from alcohols under solvent-free conditions. During this process, tungstate catalyzes the oxidation of a wide range of alcohols in the presence of TBHP as a clean source. The in-situ formed aldehydes are condensed with malononitrile and β-dicarbonyl compounds/naphthols/4-hydroxycumarin through promotion by pyridine and imidazolium moieties of the catalyst. By this method, a variety of 2-amino-3-cyano-4H-chromenes are generated in good to high yields from alcohols as inexpensive and easily available starting materials. The catalyst is recovered easily by the aid of an external magnetic field and reused in five successive runs with insignificant decreasing activity.
Highlights
A novel base-metal multifunctional nanomagnetic catalyst is prepared by the immobilization of tungstate anions onto γ-Fe2O3 supported with imidazolium moieties
This method passes through three sequential steps: (1) oxidation of alcohols to aldehydes which requires an oxidizing catalyst, (2) Knoevenagel condensation of the in-situ formed aldehydes with malononitrile, (3) Michael addition of β-dicarbonyl compounds followed by cyclization reaction
The synthesized (γ-Fe2O3-Im-Py)2WO4 was characterized by a variety of techniques such as Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), FESEM, ICP, vibrating sample magnetometer (VSM), Thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD)
Summary
A novel base-metal multifunctional nanomagnetic catalyst is prepared by the immobilization of tungstate anions onto γ-Fe2O3 supported with imidazolium moieties. The selective oxidation of alcohols to aldehydes and pyridine will activate Knoevenagel condensation-Michael addition-cyclization reaction of in-situ formed aldehydes with malononitrile and dimedone. We studied the utility of (γ-Fe2O3-Im-Py)2WO4 in the synthesis of 2-amino3-cyano-4H-chromenes via a multicomponent tandem oxidation process (Fig. 9).
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