Synthesis of the Biginelli Reaction Using a Variety of Juices As Catalyst in the Heterocyclic Chemistry Laboratory

Multicomponent reactions (MCRs) are exceptional strategies for synthesizing complex molecules, typically requiring simple experimental procedures and conditions, making them ideal for application in organic chemistry laboratories at the undergraduate level. The synthesis of heterocyclic compounds, often challenging in teaching laboratories, can be effectively achieved by developing appropriate MCR procedures. These strategies can then be properly tailored to meet the specific objectives of the corresponding experimental experience, but also to arouse students’ curiosity, enhancing their engagement in the learning process. The Biginelli reaction is a classic example of an MCR that facilitates the synthesis of dihydropyrimidinones, requiring a proton source for the reaction to proceed. In this study, three groups of students (90 in total) from a heterocyclic chemistry course conducted experiments using different natural acidic media lemon, orange, grapefruit, and pineapple juices as proton sources for two variants of the Biginelli reaction. We describe the setup of these experiments to be completed in a single 2 h laboratory session and discuss their impact on student learning. All products were fully characterized using various spectroscopic techniques such as NMR and mass spectrometry. The elucidation of the complete reaction mechanism and the chemical structures of the obtained products were integrated as activities in the experiment, enhancing the students’ understanding of green chemistry and sustainable practices in synthesis.