Table 1.
Optimization studies.
| entrya | Y | temp. | Yield (%) | dr (syn/anti) | ee (%) |
|---|---|---|---|---|---|
| 1 | 0.75 | r.t. | 55 | 5:1 | 68 |
| 2 | 1.5 | r.t | 63 | 4:1 | 84 |
| 3 | 2.0 | r.t. | 72 | 5:1 | 83 |
| 4b | 2.0 | r.t. | 53 | 3:1 | 85 |
| 5 | 2.0 | 0 °C | 48 | 3.5:1 | 95 |
| 6c | 2.0 | 0 °C | 53 | 5:1 | 94 |
| 7d | 2.0 | 0 °C | 47 | 4.7:1 | 93 |
| 8e | 2.0 | 0 °C | 43 | 3.9:1 | 96 |
| 9cf | 2.0 | 0 °C | 42 | 7.7:1 | 92 |
| 10c,g | 2.0 | 0 °C | 67 | 7.7:1 | 90 |
| 11c,h | 2.0 | 0 °C | 77 | 11:1 | −92 |
a
Unless otherwise noted, reactions performed using 15% (R,R)-2a, 30% Et2Zn and 0.2 mmol 1b in THF (0.2M).
b
Toluene as solvent.
c
Run at 0.4 M in THF.
d
Triphenylphosphine (30 mol%) used as additive.
e
Methyl 2,2-dimethyl-3-hydroxypropionate (30%) used as additive.
f
5% (R,R)-2a, and 10% diethylzinc.
g
20% (R,R)-2a, and 40% diethylzinc.
h
With (S,S)-2b.