Table 1.
Optimization of reaction conditions under ultrasound irradiation for the synthesis of 4aa.
| S.No. | Catalyst (mol%) | Solvent | Time (min) | ∗Yield (%) |
|---|---|---|---|---|
| 1 | p-TSA (10 mol %) | H2O | 35 | 50 |
| 2 | Boric acid (10 mol %) | H2O | 35 | 60 |
| 3. | Sulfamic acid (10 mol %) | H2O | 35 | 61 |
| 4 | ZnO NPs (10 mol %) | H2O | 35 | 72 |
| 5. | MgO NPs (10 mol %) | H2O | 35 | 74 |
| 6. | TiO2NPs (10 mol %) | H2O | 15 | 90 |
| 7. | Commercial TiO2 (10 mol %) | H2O | 15 | 79 |
| 8. | TiO2 NPs (10 mol %) | 1,4-dioxane | 30 | 70 |
| 9. | TiO2 NPs (10 mol %) | Acetonitrile | 30 | 72 |
| 10. | TiO2 NPs (10 mol %) | CH2Cl2 | 30 | 75 |
| 11. | Catalyst-free | H2O | 40 | traces |
| 12 | TiO2 NPs (5 mol %) | H2O | 15 | 70 |
| 13. | TiO2 NPs (15 mol %) | H2O | 15 | 90b |
Bold signifies the best reaction conditions for the present reaction.
a
Meldrum's acid (1 mmol), 3,4-(methylenedioxy)aniline (1 mmol) and 4-fluorobenzaldehyde (1 mmol), H2O (20 mL).
b
Yields of the five consequent runs by using the same TiO2 recovered NPs were 90, 89, 87, 86 and 85 %, respectively.
∗
Isolated Yield.