Table 1.
Optimization of the Reaction Conditionsa
|
|||||
|---|---|---|---|---|---|
| entry | base (equiv) | 2a (equiv) | solvent | 3 yield (%)b | 1a recovered (%)b |
| 1 | DBU (3.0) | 3.0 | CH3CN | 89 (A) | - |
| 2 | Et3N (3.0) | 3.0 | CH3CN | 10 (A) | 90 |
| 3 | DIPEA (3.0) | 3.0 | CH3CN | 12 (A) | 87 |
| 5 | K2CO3 (3.0) | 3.0 | CH3CN | 34 (B) | 60 |
| 6 | LiOtBu (3.0) | 3.0 | CH3CN | 58 (B) | 39 |
| 7 | - | 3.0 | CH3CN | 9 (B) | 90 |
| 8c | DBU (3.0) | 3.0 | CH3CN | 6 (B) | 83 |
| 9d | DBU (3.0) | 3.0 | CH3CN | - (B) | 97 |
| 10e | DBU (3.0) | 3.0 | CH3CN | 85 (B) | trace |
| 11 | DBU (2.0) | 3.0 | CH3CN | 92 (B) | trace |
| 12 | DBU (3.0) | 2.0 | CH3CN | 66 (B) | 23 |
| 13e | DBU (2.0) | 3.0 | CH3CN/H2O (1:3) | 90 (B) | 4 |
| 14e | DBU (2.0) | 3.0 | CH3CN/H2O (1:9) | 87 (B) | 6 |
| 15e | DBU (2.0) | 3.0 | H2O | 72 (B) | 15 |
a
Reaction conditions: 1a (0.2 mmol), 2a (0.6 mmol), DBU (0.6 mmol), solvent (1 mL), room temperature around the reaction flask is 35 °C (heating caused by the 456 (A) or 427 nm (B) LED lamp), under argon, 24 h.
b
Yields are based on 1a, determined by 1H NMR using dibromomethane as an internal standard.
c
The reaction was performed in the absence of PTZ.
d
The reaction was performed in the dark, covered by aluminum foil.
e
The reaction was performed in air.