An experiment exploring the chemistry of the carbonyl group for the one-step synthesis of "trans"-4,5- dibenzylaminocyclopent-2-enone is described. The reaction of furfural and dibenzylamine in the environmentally friendly solvent ethanol and catalyzed by the Lewis acid ErCl[subscript 3]·6H[subscript 2]O afforded the product in high yield (79-97%) with high purity by simple filtration. This experiment can be performed during a 3 h class, and requires only basic glassware without an anhydrous or inert atmosphere. It is suitable for use in introductory organic chemistry laboratories, where the purity of the product can be determined, using simple techniques such as TLC analysis and melting point measurement, as well as for more advanced classes allowing the consolidation of important reactivity features of the carbonyl group and the interpretation of the [superscript 1]H NMR spectrum.