Niobium oxide-mediated catalysis49.
| ||||||
|---|---|---|---|---|---|---|
| Entry | R1 | R2 | R3 | Time (h) | Conversiona (%) | Yield (%) |
| 1 | Me | Et | H2C CHCH2 | 6 | 65 | 52 |
| 2 | Me | Me | H2C CHCH2 | 6.5 | 70 | 58 |
| 3 |
|
H2C CHCH2 | 8 | 85 | 57 | |
| 4 | Me | Et |
|
5 | 75 | 58 |
| 5 | Me | Me |
|
5.5 | 80 | 76 |
| 6 |
|
|
8 | 70 | 63 | |
| 7 | Me | Me | n Bu | 5.5–7 | 100 (100, 100)b | 98 (93, 87)b |
| 8 | Me | Me | t Bu | 8 | 93 | 60 |
| 9 | Me | Me | iPr | 8 | 81 | 63 |
| 10 | Me | Me | Bn | 12 | 50 | 33 |
| 11 |
|
(−)-Menthyl | 8 | 65c | 61c | |
Conversion determined by GC of the crude reaction mixture.
Catalyst was recovered and reused three times without appreciable activity loss.
Diester product.