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

Table 7

Reusability of the catalyst for the synthesis of 3,3-dimethyl-(7S, 11R)-diphenyl-2,4-dioxa-8,10-diazaspiro[5.5]undecane-1,5,9-trione^a.

Cycle	0	1st	2nd	3rd	4th
Time (min)	7	7	8	9	9
Yield (%)^b	80	78	76	73	71

 ^aReaction 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.
^bIsolated yields.