Effects of various catalysts and different amounts of CeCl3·7H2O on the yield of compound 4ja.
| Entry | Catalyst (mol%) | Yield (%) |
|---|---|---|
| 1 | — | 0 |
| 2 | AcOH (30) | 44 |
| 3 | ZnCl2 (30) | 32 |
| 4 | Sc (OTf)3 (30) | 51 |
| 5 | NH2SO3H (30) | 60 |
| 6 | p-TsOH (30) | 70 |
| 7 | MgCl2 (30) | 37 |
| 8 | MeSO3H (30) | 31 |
| 9 | H2SO4 (30) | 32 |
| 10 | CeCl3·7H2O (20) | 65 |
| 11 | CeCl3·7H2O (30) | 75 |
| 12 | CeCl3·7H2O (40) | 75 |
| 13 | CeCl3·7H2O (50) | 75 |
a
Reaction conditions: 5-chloroisatin (1 mmol), 3-amino-4-bromo-1H-pyrazole (1 mmol), tert-butyl isocyanide (1 mmol) and ethanol (3 mL), reaction time: 24 h.