Brønsted Acid Saponin Combined Catalyst (BASapC) for the Synthesis of Diverse 1,1‐Dihomoarylmethane Scaffolds in Aqueous Solution

Abstract The present study describes the synthesis of various bioactive compounds, including bis‐coumarins, bis‐lawsones, bis‐dimedones, and bis‐indolylmethanes, using a novel catalytic system called “Brønsted acid saponin combined catalyst” (BASapC). The BASapC was formed by combining p ‐toluenesulfonic acid (PTSA) and saponin in an aqueous medium. The prepared BASapC proved to be effective in facilitating cascade‐type Knoevenagel–Michael addition reactions between various aromatic aldehydes with 4‐hydroxycoumarin, lawsone, dimedone, or indole at 80 °C. In the BASapC system, PTSA acted as a powerful Brønsted acid, activating reactants, whereas saponin served as a natural surfactant, enhancing the solubility of organic compounds in water. This catalytic approach established a straightforwardness and robustness of diversity‐oriented synthesis (DoS), delivering the desired products with good to excellent yields. Additionally, the BASapC exhibited recyclability for at least four cycles without significant loss of activity.