1.
Optimization of reaction conditions.[a]
| Entry | (S)-7 [mol %] | Time/Temp [h/°C] | Yield [%][b] | i.r. [3a:4a][c] | ee [%][d] |
|---|---|---|---|---|---|
| 1[e] | 10 | 22/RT | 28 | 12:1 | 94 |
| 2[e] | 20 | 17/RT | 47 | ca. 10:1 | 94 |
| 3 | 20 | 2/110 | 72 | 4:1 | 85 |
| 4 | 20 | 21/60 | 55 | 7:1 | 92 |
| 5 | 20 | 21/80 | 66 | 5:1 | 89 |
| 6 | 10 | 22/80 | 25 | 5:1 | n.d.[f] |
| 7 | 20 | 3/RT then 21/110 | 83 | 4:1 | 91 |
| 8 | 20 | 3/RT then 21/80 | 77 | 5:1 | 93 |
[a] 1 a (0.1 mmol), 2 a (0.15 mmol), and (S)-7 in toluene (1.0 mL). [b] Isolated yield of 3 and 4 after FC. [c] i.r.=regioisomeric ratio; determined by 1H NMR spectroscopy of the crude reaction mixture. [d] Determined on 5 a by HPLC analysis using a chiral stationary phase. [e] Performed under argon; with 2 a (0.2 mmol) and toluene (0.5 mL). [f] n.d.=not determined.