Table 1. Survey of Reaction Conditionsa.
| entry | ammonium salt (equiv) | solvent | time/h | 3a/% |
|---|---|---|---|---|
| 1 | NH4OAc (5.0) | PEG-400 | 4 | 88 |
| 2 | NH4OAc (3.0) | PEG-400 | 5 | 90 |
| 3 | NH4OAc (1.0) | PEG-400 | 5 | 85 |
| 4 | NH4OAc (3.0)/80 °C | PEG-400 | 5 | 83 |
| 5 | NH4OAc (3.0)/120 °C | PEG-400 | 4 | 87 |
| 6 | NH4OAc (3.0)/Air | PEG-400 | 3 | 70 |
| 7 | NH4OAc (3.0)/O2 | PEG-400 | 5 | 80 |
| 8 | NH4OAc (3.0)/DDQ (2.2) | PEG-400 | 6 | 0b |
| 9 | NH4F (3.0) | PEG-400 | 5 | 83 |
| 10 | FeSO4(NH4)2SO4·6H2O (3.0) | PEG-400 | 5 | 80 |
| 11 | NH4VO3 (3.0) | PEG-400 | 5 | 78 |
| 12 | NH4HCO3 (3.0) | PEG-400 | 5 | 86 |
| 13 | (NH4)2SO4 (3.0) | PEG-400 | 5 | 85 |
| 14 | NH4OAc (3.0) | DMSO | 5 | 80 |
| 15 | NH4OAc (3.0) | EtOH | 5 | 40 |
| 16 | NH4OAc (3.0) | [BMIM]BF4 | 5 | 70 |
| 17 | NH4OAc (3.0) | [BMIM]PF6 | 5 | 65 |
a
Unless otherwise indicated, all reactions were carried out in a sealed tube with 1a (0.5 mmol) and 2a (0.55 mmol) in solvent (3 mL) at 100 °C under N2.
b
1,5-Bis(4-chlorophenyl)-6-phenyl-1,5,6,7-tetrahydro-4H-pyrrolo[3,2-c]pyridin-4-one (4a) was isolated in 90% yield.