FeCl3-catalysed ultrasonic-assisted, solvent-free synthesis of 4-substituted coumarins. A useful complement to the Pechmann reaction

• FeCl3 an efficient catalyst for the ultrasound-assisted Pechmann reaction.
• High yields, short reaction times and solvent-free conditions.
• Comparison of ultrasound- and microwave-assisted conditions.

The catalytic activity of FeCl3 for the synthesis of a variety of 4-substituted coumarins using high energy techniques has been investigated. The ultrasonic-assisted conditions provide a useful complement to the Pechmann reaction, affording the coumarin derivatives in excellent yields, under solvent-free conditions, in short reaction times using an inexpensive, mild and benign Lewis acid catalyst.