Natural phosphate as an efficient and green catalyst for synthesis of tetraketone and xanthene derivatives

Natural phosphate was applied as an efficient and ecofriendly catalyst for the synthesis of tetraketones (2–2.5 h, 90–100 %) and xanthenes (6.5–8.5 h, 84–95 %) via Knoevenagel–Michael cascade reaction of aromatic aldehydes with 1,3-cyclic diketones in water and ethanol, respectively. This protocol provides several advantages over the traditional chemical synthesis, such as simple work-up, easy handling procedure, non-toxicity and stability of catalyst, low cost and environmental friendliness.