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| Entry | Solvents | Time (h) | Yield (%) |
|---|---|---|---|
| 1 | Water | 3.0 | 90 |
| 2 | Toluene | 5.0 | 40 |
| 3 | DMF | 7.5 | 41 |
| 4 | Ethanol | 4.0 | 35 |
| 5 | Acetonitrile | 5.5 | 40 |
| 6 | THF | 5.0 | 53 |
Reaction conditions: 4-hydroxy coumarin (5 mmol), benzaldehyde (5 mmol) and urea (5 mmol) using l-proline (10 mol%).
