CeCl₃⋅7H₂O/SiO₂ as an Efficient and Recyclable Catalyst for the Synthesis of Dihydropyrano[3,2-b]chromenediones

Table 1

Synthesis of 2-(hydroxymethyl)-7,7-dimethyl-10-phenyl-7,8-dihydropyrano[3,2-b]chromene-4,9(6𝐻,10𝐻)-dione in the presence of a variety of catalysts^a.

Entry	Catalysts	Time/min	Yield/%^b
1	—	240	0
2	I2 (5 mol%)	60	19
3	p-TsOH (5 mol%)	60	29
4	H2SO4 (5 mol%)	90	11
5	HOAc (5 mol%)	90	32
6	CeCl3 (5 mol%)	60	84
7	ZnCl2 (5 mol%)	60	80
8	CeCl3·7H2O/SiO2 (1 mol%)	90	63
9	CeCl3·7H2O/SiO2 (2 mol%)	60	70
10	CeCl3·7H2O/SiO2 (3 mol%)	60	79
11	CeCl3·7H2O/SiO2 (4 mol%)	45	89
12	CeCl3·7H2O/SiO2 (5 mol%)	45	95
13	CeCl3·7H2O/SiO2 (6 mol%)	45	94
14	CeCl3·7H2O/SiO2 (7 mol%)	45	93

^aReaction conditions: kojic acid (1 mmol); benzaldehyde (1 mmol); dimedone (1 mmol); neat; 110°C.
^bIsolated yield.