Silica tungstic acid (STA) as a highly efficient and reusable catalyst for the synthesis of benzoxanthenes under solvent-free conditions in ultrasonication

An environmentally benign, ultrasound-promoted synthesis of biologically active benzoxanthene derivatives has been developed by silica-supported tungstic acid as an efficient catalyst under solvent-free conditions. The major advantages of the present protocol are operational simplicity, use of an inexpensive catalyst, bypassing the chromatographic purification, good yields, and short reaction times. The catalyst could be reused at least five consecutive cycles, without loss of its catalytic activity.