Effective and Green Synthesis of Flavanones in Tap Water

Background: Flavanones are known to exhibit numerous biological properties, such as antimicrobial, antitumor, antioxidant and anti-inflammation. Synthesis of these flavanones has attracted much attention in the past few decades. Although some catalyst systems have been developed to synthesize flavanones, some disadvantages of those methods still exist, including harsh reaction conditions, tedious work-up, a lot of unfriendly reaction solvents used. Some paper reported that the reaction could proceed in aqueous solution, however, it was hard to achieve the results as they reported that some methods lacked good repeatability. Methods: We used tap water as the reaction medium and used KOH (0.1 equiv.) as the catalyst. The reaction conditions were systematically investigated. Nine chalcones were tested which could be converted into the corresponding flavanones at 50 °C or 80 °C with moderate to good yield. Results: Nine flavanones were successfully synthesized in basic water solution at 50 °C or 80 °C. Especially, seven of them were obtained as pure products simply after filtration without additional workup. All of the products were confirmed by 1H NMR and 13C NMR. Conclusion: We have developed an efficient and reliable catalytic system for the cyclization of chalcones to flavanones in tap water. The method was characterized by rapidity, accuracy and good replication. In addition, the simple work up procedure makes the current reaction practically useful.