Application 3-sulfonic acid 1-imidazolopyridinium 2-hydrogen sulfate as an efficient catalyst for the synthesis of 4,4′-(arylmethylene)bis(1 H-pyrazol-5-ols)

Pyrazolones and bis-pyrazolones have been paid much attention for their various biological activities such as the selective COX-2 inhibitory, antitumor, and cytokine inhibitory ones [1]. In recent years, ionic liquids (ILs) have become powerful alternatives to the conventional molecular organic solvents due to their particular properties such as the ability to dissolve many organic and inorganic substances [2]. Herein we report the use of the mild, rapid, efficient, and environmentally friendly 3-sulfonic acid imidazolopyridinium hydrogen sulfate [Simp]HSO4[3] catalyst for the preparation of 4,4 -(arylmethylene)-bis-(3-methyl-1-phenyl- 1H-pyrazol-5-ols) from the solvent-free reaction of aromatic aldehydes with two equivalents of 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one in EtOH at room temperature.