Ru-Hydroxyapatite: An Efficient and Reusable Catalyst for the Multicomponent Synthesis of Pyranopyrazoles under Facile Green Conditions

An efficient, green and facile protocol for the synthesis of pyranopyrazole derivatives through the reaction of aromatic aldehydes, malononitrile, hydrazine hydrate and ethyl acetoacetate was developed using Ru loaded hydroxyapatite (Ru-CaHAp) as catalyst. The eco-friendly one-pot reactions in an ethanol-water mixture are fast (approximate to 15 min) and occur at room temperature. The catalyst was fully characterized by various techniques. The chemical structures of the synthesized compounds were identified and confirmed by H-1, N-15 and C-13 NMR, FT-IR and HR-MS spectral data. The noteworthy advantages offered by this method are an environmentally-friendly simple procedure, mild conditions, short reaction times, recycling of catalyst and good to excellent (89 to 98%) yield of products.