An efficient, atom-economical, four-component one-pot reaction method was developed
for pyrano[2,3-c]pyrazole-3-carboxylates using dimethylacetylenedicarboxylate,
hydrazine hydrate, malononitrile and aromatic aldehydes, using a RuCaHAp catalyst. Ten
new substituted pyrano[2,3-c]pyrazole-3-carboxylate derivatives (5a-k) were synthesized in
good to excellent yields (88 to 97%), at room temperature with short reaction times ( 30
min) using the green solvent aqueous ethanol. RuCaHAp was prepared and characterized by
various techniques including SEM, TEM, P-XRD and BET spectroscopy. The proposed heterogeneous
catalyst that can be easily synthesized, is inexpensive and stable with good reusability
(at least 6 times) showing marginal loss of activity. The suggested environmentally
benign protocol offers high yields, clean reaction profiles, operational simplicity and no need
for chromatographic separations.
Keywords: Green protocol, multicomponent reaction, heterogeneous catalyst, Ru hydroxyapatite, pyrano[2, 3-c]pyrazoles, recyclable.
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