N-Sulfopiperidine-4-Carboxylic Acid Functionalized Fe3O4 Nanoparticles as Catalyst for One-Pot Synthesis of Dipyrromethanes under Solvent-Free Condition

In recent years, dipyrromethanes and its derivatives have aroused a strong interest due to theiruseful physiological properties and biological activities as important building blocks for thesynthesis of porphyrins, calixpyrrols and corroles [1]. As a consequence, the synthesis andthe applications of dipyrromethane derivatives still attract the attention of organic chemists.The most common strategy involved in the synthesis of dipyrromethanes is the mixture ofpyrrole (2 mmol) and ketone (1 mmol) or aldehyde (1 mmol) compounds. Of the various othermethods, syntheses involving transition-metal salts or lewis acid have recently been describedfor the preparation of substituted dipyrromethane derivatives [2-4]. In connectionwith our ongoing studies, we wish, herein, to report on the use of Chlorosulfonic acid supportedPiperidine-4-carboxylic acid (PPCA) functionalized Fe3O4 nanoparticles (Fe3O4-PPCA) as a more robust and efficient catalyst in the one-pot synthesis of dipyrromethane derivatives(3a-j) by the reaction of pyrrole (1) and ketone or aldehyde (2a-j) under solvent freeconditions (Fig. 1). (***) The main advantages of the presented protocol are mild, clean and environmentally benignreaction conditions, as well as the high yields, simple work-up, ease of separation, and recyclabilityof the magnetic catalyst.