A Fast, Highly Efficient, and Green Protocol for Synthesis of Biscoumarins Catalyzed by Silica Sulfuric Acid Nanoparticles as a Reusable Catalyst

Table 1

Synthesis of 4a under various conditions.

Entry	Catalyst (amount)	Cond./Sol.	Time (min)	Yield^a (%)	Reference
1	I2 (10 mol%)	100°C/H2O	25	97	[6]
2	TBAB^b (4 mol%)	120°C/—	20	85	[7]
3	[bmim]BF4 (4 mmol)	60–70°C/—	120	84	[8]
4	SDS^c (0.2 mol, 57.6 mg)	60°C/H2O	140	90	[9]
5	[PSebim][OTf] (0.5 mol%)	70°C/—	120	95	[10]
6	[MIM(CH2)4SO3H][HSO4](3 mol%)	80°C/—	30	92	[11]
7	SiO2-OSO3H NPs (0.001 g)	80°C/EtOH	20	89	—
8	SiO2-OSO3H NPs (0.003 g)	80°C/EtOH	20	93	—
9	SiO2-OSO3H NPs (0.005 g)	80°C/EtOH	20	93	—
10	SiO2-OSO3H NPs (0.003 g)	100°C/H2O	20	87	—
11	SiO2-OSO3H NPs (0.003 g)	40°C/CH2Cl2	20	82	—
12	SiO2-OSO3H NPs (0.003 g), 2nd run	80°C/EtOH	20	89	—
13	SiO2-OSO3H NPs (0.003 g), 3rd run	80°C/EtOH	20	87	—

aIsolated yield, ^btetrabutylammonium bromide, and ^csodium dodecyl sulfate.