Silica supported sodium hydrogen sulfate (NaHSO4-SiO2): A novel, green catalyst for synthesis of pyrazole and pyranyl pyridine derivatives under solvent-free condition via heterocyclic β-enaminones

NaHSO4-SiO2 is used as an efficient, mild and reusable catalyst for the synthesis of novel heterocyclic pyrazole (5a-h) and pyranyl pyridine (7a-h) derivatives via heterocyclic beta-enaminones (3a-d) under thermal solvent-free conditions. The remarkable features of this green, new methodology are high conversions, cleaner reaction profile, simple experimental and work-up procedures. Structures of the newly synthesized compounds have been elucidated on the basis of elemental analysis and spectral data (IR, H-1 NMR, C-13 NMR and mass spectrometry). The catalyst is characterized for the first time by using scanning electron microscopy-energy dispersive X-ray (SEM-EDX) and powder XRD. The catalyst can be reused several times without significant loss of its catalytic activity. (c) 2012 Elsevier B.V. All rights reserved.