Table 1.
Reaction optimization.
| Entry | 6 (mol%) | Aryl Ester | Base | Yield (%) | dr (7:8) | er (7) | er (8) |
|---|---|---|---|---|---|---|---|
| 1 | 20 | 1 | i-Pr2NEt | 82 | 55:45 | 97:3 | 94:6 |
| 2 | 0 | 1 | i-Pr2NEt | 0 | - | - | - |
| 3 | 20 | 1 | Et3N | 98 | 60:40 | 97:3 | 94:6 |
| 4 | 20 | 2 | Et3N | 99 | 65:35 | 81:19 | 94:6 |
| 5 | 20 | 3 | Et3N | 88 | 60:40 | 94:6 | 91:9 |
| 6 | 20 | 4 | Et3N | 31 | 55:45 | 84:16 | 71:29 |
| 7 | 5 | 1 | Et3N | 95 | 55:45 | 93:7 | 88:12 |
| 8 [a] | 5 | 1 | Et3N | 99 | 60:40 | 92:8 | 85:15 |
| 9 [a] | 5 | 1 | none | 90 | 60:40 | 93:7 | 89:11 |
All reactions were carried out on a 0.25 mmol scale; isolated yields are a mixture of diastereoisomers 7 and 8; dr was determined by 1H NMR spectroscopic analysis of the crude reaction mixture; er was determined by CSP-HPLC analysis: 7 (2S,1′R:2R,1′S) and 8 (2S,1′S:2R,1′R). [a] Reaction performed at 40 °C.