Four-component synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione derivatives

An efficient synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione derivatives from the four-component condensation of dimedone, arylaldehyde, hydrazine monohydrate, and phthalic anhydride using reusable ionic liquids, 2-pyrrolidonium hydrogensulfate, (4-sulfobutyl)tris(4-sulfophenyl)phosphonium hydrogensulfate and triphenyl(propyl-3-sulphonyl)phosphonium toluenesulfonate as acidic catalysts have been investigated.