Citric acid, a green catalyst for the one-pot, multi-component synthesis of highly substituted piperidines

Citric acid has been used as a green and efficient catalyst for one-pot, multi-component synthesis of highly substituted piperidines by condensation of aromatic aldehydes, aromatic amines, and beta-ketoesters in MeOH at ambient temperature. This method has several advantages including use of a nonhazardous and inexpensive catalyst, easy work-up, clean reaction conditions, and high yields.