A facile one-pot green synthesis of piperidines by acidic ionic liquid (4-sulfobutyl)-tris (4-sulfophenyl) phosphonium hydrogen sulfate

Synthesis of six-membered nitrogen heterocyclic compounds such as piperidines and their analogues is very important owing to their biological activities such as antimalarial, antihypertensive, antibacterial, anticonvulsant and anti-inflammatory agents [1, 2]. Furthermore, green synthesis of these compounds is very important at this time. Ionic liquids are receiving a widespread attention as mediums, because of their unique properties for green chemistry reactions such as a wide liquid range, non-flammability, non-volatile, thermal stability, low vapor pressure, and the ease of handling [3, 4]. Thus, an efficient green and one-pot procedure for the preparation of piperidine derivatives from five-component reactions of aromatic aldehydes, substituted anilines, and ethyl/methyl acetoacetate (molar ratio: 2/2/1) in the presence of acidic ionic liquid (4-sulfobutyl)-tris (4-sulfophenyl) phosphonium hydrogen sulfate as the catalysts at 80°C under solvent-free conditions has been developed [5]. Piperidines were obtained in high yields with simple green procedure and short reaction time (Fig. 1).