A bifunctional ionic liquid, 1,4-dimethyl(4-sulfobutyl)piperazinium hydrogen sulfate ([DMSBP][HSO4], 1), containing both acid and basic sites was prepared. This ionic liquid was used as a homogeneous and reusable catalyst and efficiently promoted synthesis of 1H-indazolo[1,2-b]phthalazinetriones (5a–m) in a one-pot, four-component condensation reaction of phthalic anhydride, hydrazinium hydroxide, dimedone, and aromatic aldehydes under solvent-free conditions at 80 C. Advantages of the method include short reaction time, high yields, and simple purification.
