Ultrasound-promoted catalyst-free one-pot four component synthesis of 2H-indazolo[2,1-b]phthalazine-triones in neutral ionic liquid 1-butyl-3-methylimidazolium bromide

A catalyst-free one-pot four component methodology for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones under ultrasonic irradiation at room temperature using 1-butyl-3-methylimidazolium bromide, [Bmim]Br, as a neutral reaction medium is described. A broad range of structurally diverse aldehydes (aromatic aldehydes bearing electron withdrawing and/or electron releasing groups as well as heteroaromatic aldehydes) were applied successfully, and corresponding products were obtained in good to excellent yields without any byproduct.

► Application of catalyst-free conditions.
► Application of ultrasonic irradiation.
► Application of a neutral ionic liquid.
► Generality and simplicity of the method.
► Environmental compatibility and recoverability of the reaction medium.