Green and Convenient Synthesis of Polyfunctionalized Piperidines Catalyzed by Ascorbic Acid under Ambient Temperature

A green and mild synthetic route to the convenient preparation of polyfunctionalized piperidines have been developed using ascorbic acid as a green and biodegradable catalyst via Knoevenagel- intramolecular [4+2] aza-Diels-Alder imin-based reaction in ethanol media. All reactions are completed by a five-component condensation reaction between 1,3-dicarbonyl compounds, aromatic aldehydes and various amines in short period of times and the products are obtained in good to high yields. The salient features of this environmentally friendly approach are green, biodegradable and readily available catalyst, straightforward work-up with no column chromatographic separation, mild reaction conditions, high atom-economy, avoidance of toxic organic solvents and highly efficient.