One-pot three-component synthesis of highly substituted piperidines using 1-methyl-2-oxopyrrolidinium hydrogen sulfate

1-Methyl-2-oxopyrrolidinium hydrogen sulfate ([Hpyro][HSO4]) is used as an ionic liquid catalyst for the one-pot three-component synthesis of highly substituted piperidines from aromatic aldehydes, anilines and beta-ketoesters in refluxing ethanol. This homogeneous catalyst procedure has the advantages of easy work-up, no need for column chromatography, simple and readily available precursors, and good to high yields.