Table 1. Reaction Optimization Studiesa.
| entry | catalyst (mol %) | solvent, temp | 2ab | 3ab |
|---|---|---|---|---|
| 1c,d | MsOH (10 mol %) | DCE, rt | - | - |
| 2d | MsOH (10 mol %) | DCE, 60 °C | 20 | 35 |
| 3c,d | p-TSA (10 mol %) | DCE, rt | - | - |
| 4d | p-TSA (10 mol %) | DCE, 60 °C | 8 | 25 |
| 5c,d | PPTS (10 mol %) | DCE, rt | - | - |
| 6c,d | PPTS (10 mol %) | DCE, 60 °C | - | - |
| 7d | TFA (10 mol %) | DCE, 60 °C | 10 | 32 |
| 8d | TfOH (10 mol %) | DCE, 60 °C | 10 | 25 |
| 9c,d | AcOH (10 mol %) | DCE, 60 °C | - | - |
| 10c,d | CSA (50 mol %) | DCE, rt | - | - |
| 11c,d | CSA (50 mol %) | DCE, 60 °C | - | - |
| 12c,d | l-proline (10 mol %) | DCE, 60 °C | - | - |
| 13c,d | (R)-BINOL-phosphoric acid (10 mol %) | DCE, 60 °C | - | - |
| 14e | MsOH (50 mol %) | DCE, 60 °C | 24 | 70 |
| 15e | MsOH (100 mol %) | DCE, 60 °C | 20 | 68 |
| 16c,d | MsOH (10 mol %) | CH3CN, rt | - | - |
| 17c,d | MsOH (10 mol %) | CH3CN, 60 °C | - | - |
| 18c,d | MsOH (100 mol %) | CH3CN, rt | - | - |
| 19c,d | MsOH (100 mol %) | CH3CN, 60 °C | - | - |
| 20c,d | no catalyst | DCE, 60 °C | - | - |
a
Reaction conditions unless otherwise specified: 1a (0.5 mmol) was used in 2 mL of solvent.
b
Isolated % yields.
c
No conversion was observed.
d
The reaction time is 24 h.
e
The reaction time is 5 h. DCE = dichloroethane.