An Efficient One-Pot Green Protocol for the Synthesis of 5-Unsubstituted 3,4-Dihydropyrimidin-2(1H)-Ones Using Recyclable Amberlyst 15 DRY as a Heterogeneous Catalyst via Three-Component Biginelli-Like Reaction

Table 1

Catalytic activity of different ion exchange resins in Biginelli condensation^a.

Entry	Ion exchange resin	Reaction time (h)	Yield (%)
1	—	10	Trace
2	Amberlyst-70	3	81
3	Amberlyst 15 DRY^a	5.5	94
4	Indion-130	3	92.5
5	Indion-190	3.5	92
6	Nafion-H	4.5	85
7	Envirocat EPZ10	6	84
8	Montmorillonite KSF	10	38

^aReaction conditions: ethyl acetoacetate (1.0 mmol), benzaldehyde (1.0 mmol), and urea (1.2 mmol) in dry ethanol (10 mL), ion exchange resin (50 mg) at refluxing temperature.