A Facile One-Pot and Green Multi-Component Synthesis of 2-Amino-4H-pyrans Promoted by Pyridinium p-Toluenesulfonate in Aqueous Medium

Background: 4H-benzo[b] pyran derivatives have attracted great interest due to biological and pharmacological properties including antimicrobial, antiviral, antipro liferative, sex pheromone, antitumor, cancer therapy, central nervous system activity and other interesting biological activities. For these reasons several synthetic methods are reported. For our part we want to propose an efficient procedure which respects the environment. Method: To achieve our study we performed a one-pot three-component reaction of aromatic aldehydes, dimedone, malononitrile and pyridinium p-toluenesulfonate as catalyst under different conditions. Results: We found that the optimal conditions for the preparation of 2-amino-4H-benzo[b] pyrans catalyzed by p-toluenesulfonate pyridinium are in refluxed water and with 10 mol% of catalyst. Given these results and to show the generality of the procedure, we applied the optimized reaction conditions for the synthesis of various 2-amino-4H-benzo[b] pyrans from a range of substituted aromatic and heteroaromatic aldehydes. The desired products are obtained in good to excellent yields. Conclusion: We have synthesized a variety of 4H-benzo[b] pyran derivatives according to a three component reaction between aromatic aldehydes, dimedone and malononitrile using pyridinium p-toluenesulfonate as a catalyst. This method gives very good yields and has the merit of simplicity, respect for the environment by using water as solvent and an available and inexpensive catalyst.