Synthesis of a diversified combinatorial library of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives applying sustainable carbon-based solid acid catalyst involving a domino four-component reaction

A SO3H-bearing carbonaceous solid catalyst has been synthesized through sulfonation followed by the hydrothermal carbonization method from renewable resource polyethylene glycol. The biodegradable catalyst was characterized by XRD, TEM, FT-IR, and energy dispersive X-ray. The surface area and pore diameter of the catalyst were determined by a nitrogen adsorption-desorption isotherm experiment. A highly efficient multicomponent heteroannulation protocol for the synthesis of a library of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives has been developed by applying the solid acid catalyst. This synthesis was established to follow the group-assistant-purification chemistry process avoiding traditional chromatography. The aqueous reaction medium, easy recovery of the catalyst, and high yield of the products make the protocol attractive, sustainable, and economic. This work may not only lead to environmentally benign systems, but also will provide a new aspect of organic chemistry in water.