Microwave-Assisted Synthesis of Spirofused Heterocycles Using Decatungstodivanadogermanic Heteropoly Acid as a Novel and Reusable Heterogeneous Catalyst under Solvent-Free Conditions

Table 5

Effect of the microwave power and the irradiation time on the formation of 1a.

Entry	Time (min)	Power (W)	Yields (%)
1	4	250	47
2	4	300	52
3	4	400	55
4	4	500	58
5	4	600	63
6	4	700	69
7	4	750	71
8	4	800	74
9	4	900	80
10	2	900	36
11	3	900	62
12	5	900	88
13	7	900	97
14	8	900	94
15	9	900	92

Reaction conditions: benzaldehyde (0.30 g, 2 mmol), Meldrum’s acid (0.144 g, 1 mmol), urea (0.06 g, 1 mmol), and decatungstodivanadogermanic acid (0.03 g, 3 mmol) in microwave irradiation at 80°C under solvent-free condition.