The development of novel, high-yielding, and selective methodologies for the asymmetric synthesis of stereocenters is at the forefront of modern synthetic chemistry research. Organocatalysis can now be viewed as a viable alternative to the use of the sometimes toxic transition-metal catalysts. In this experiment, the simple synthesis of an achiral imidazolidinone organocatalyst is described and its performance is compared to that of a related commercially available chiral catalyst in a Diels-Alder cycloaddition. The organocatalyst operated via an iminium ion intermediate and the product of the Diels-Alder cycloaddition was purified by silica plug filtration (no flash column chromatography required). The diastereoselectivity was readily measured with [superscript 1]H NMR spectroscopy and optionally, the enantioselectivity of the chiral catalyst can be assessed with chiral GC. The experiment can be performed over three laboratory sessions and is suitable for a third- or fourth-year undergraduate laboratory curriculum. The experiment demonstrated not only the synthesis of an organocatalyst but also the effect and importance of catalyst design on the stereochemical outcome of a Diels-Alder cycloaddition.