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

Table 2

Preparation of dihydropyrano[3,2-b]chromenes^a.

Entry	R	Time/min	Product	Yield/%^b	m.p./°C (Lit.)
1	C6H5	40	4a	95 (93, 89)^c	184-185 (186-188)^11
2	4-Cl-C6H4	40	4b	96	205-206
3	4-F-C6H4	40	4c	93	161-162 (160-164)^11
4	4-NO2-C6H4	30	4d	95	229-230
5	3-NO2-C6H4	30	4e	96	212-213
6	2-Cl-C6H4	40	4f	92	216-217
7	2,4-Cl2-C6H3	40	4g	90	166-167
8	3,4,5-(MeO)3-C6H2	60	4h	86	174-175
9	2,5-(MeO)2-C6H3	60	4i	86	192-193
10	4-Me-C6H4	45	4j	89	214-215
11	4-MeO-C6H4	45	4k	88	178-179 (180-182)^11

^aReaction conditions: kojic acid (1 mmol); aldehyde (1 mmol); dimedone (1 mmol); CeCl₃·7H₂O/SiO₂ (0.05 mmol); neat; 110°C.
^bIsolated yield.
^cThe catalyst was reused for three runs.
¹¹It is m.p. of compound in Literature 11.