Table 5. Comparing the Catalytic Activity of ZnO-ZnS over Other Mediators in the Preparation of Chromeno[4, 3-b]chromene.

catalyst	catalyst amount	time (h)	temp (°C)	solvent	yield (%)
Lewis acid-surfactant-combined catalyst41	10 mol %	1.5	70	H2O (2.5 mL)	90
immobilized molybdic acid onto 3-chloropropyl-grafted magnetic silica-coated Fe3O442	0.002 g	0.75	80		90
chlorosulfonic acid immobilized on CuFe2O443	(0.05 g)	2.5	70	EtOH (5 mL)	90
ZrO244	10 mol %, 12.3 mg	0.5	80	H2O (5 mL)	91
ZnO-ZnS [this work]	10 mg	30	r.t. green LED	- CH3CN (5 mL)	87

Reaction conditions are described below Table 1.