An efficient synthesis of bisenols in water extract of waste onion peel ash

Bisenols and its derivatives are attractive heterocyclic compounds exhibiting a wide range of biological properties, including anticancer, antipyretic and antimicrobial characteristics. Many catalytic systems have been reported to enhance the synthesis of bisenols, but these catalytic systems suffer from several drawbacks, such as the use of external metals, expensive and toxic chemicals. Thus, the development of a greener and efficient catalyst for the synthesis of bisenols is highly sought after. Herein, an improved protocol for the synthesis of bisenols in the water extract of burned-ash of onion peel waste (ash-water extract) as an efficient catalytic system is reported. Upon completion of the reaction, the crude mixture was extracted with ethyl acetate and the ash-water extract was successfully reused for several times in the synthesis of a variety of bisenols. Bisenols were obtained in good to excellent yields (62-94%) by using various benzaldehyde and 4-hydroxycoumarin catalyzed by the ash-water extract. Moreover, all pure products were obtained by precipitation without the need of column purification.