A Highly Efficient Tandem Knoevenagel/Michael Reaction Using Mohr’s Salt Hexahydrate as a Green and Powerful Catalyst: Selective Synthesis of Benzylpyrazolocoumarins on Water

In this work, new, efficient, and environmentally adapted synthesis of benzylpyrazolocoumarins in one‐pot is introduced. From tri‐component reaction of a wide range of aryl aldehydes, 4‐hydroxycoumarin, and 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one on water, benzylpyrazolocoumarins with good to excellent yields in a green procedure were synthesized. The highly efficient role of ferrous ammonium sulfate hexahydrate (Mohr’s salt) as a new green catalyst in this synthesis is obviously demonstrated. This novel procedure is an effective, cheap and environmentally adapted route to the synthesis of benzylpyrazolocoumarin derivatives. The crude products recrystallized to afford the crystalline pure product. This novel procedure has some advantages such as high efficiency, simplicity, high rate and environmental safety.