Table 1.
Optimization of enantioselective Diels-Alder reactiona
| |||||
|---|---|---|---|---|---|
| Entry | Catalyst | Solvent | Yield[%]b | d.r.b | e.r.c |
| 1 | 1a | PhMe | <5 | -- | -- |
| 2 | 1b | PhMe | <5 | -- | -- |
| 3 | 1c | PhMe | 72 | 6:1 | 75:25 |
| 4 | 1c | DCM | 44 | 10:1 | 50:50 |
| 5 | 1c | THF | <5 | -- | -- |
| 6 | 1c | Et2O | <5 | -- | -- |
| 7 | 1d | PhMe | <5 | -- | -- |
| 8d | 1e | PhMe | <5 | -- | -- |
| 9d,e | 1e | DCM | 53 | 6:1 | 51:49 |
| 10d | 1e | PhCF3 | 25 | 6:1 | 50:50 |
| 11d | 1e | DCM:PhMe (9:1) | 25 | 6:1 | 53:47 |
a
Reactions were carried out in dry PhMe [0.2 M] in a cooling bath, with strips of blue LEDs (λmax = 470 nm) coiled around the reactions (see supporting information for details).
b
Determined by 1H NMR spectroscopic analysis of the crude reaction mixture relative to the internal standard (Me3Si)2O.
c
Determined by HPLC analysis of purified material using a chiral stationary phase.
d
Reaction performed using a 2.5 mol % catalyst loading.
e
Reaction performed at −30 °C.