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| Entry | Catalysts | Time (h) | Yield (%) |
|---|---|---|---|
| 1 | l-Proline (2 mol%) | 8.0 | 61 |
| 2 | l-Proline (5 mol%) | 4.0 | 77 |
| 3 | l-Proline (10 mol%) | 3.0 | 90 |
| 4 | l-Proline (15 mol%) | 3.0 | 90 |
| 5 | p-TSA (10 mol%) | 10.0 | 49 |
| 6 | TEA (10 mol%) | 8.0 | 59 |
| 7 | CaCl2 (10 mol%) | 10.0 | 60 |
| 8 | H2SO4 (10 mol%) | 160 | 70 |
| 9 | Sulphamic acid (10 mol%) | 180 | 42 |
Reaction conditions: 4-hydroxy coumarin (5 mmol), benzaldehyde (5 mmol) and urea (5 mmol) using water.
