Table 1.
Optimization of the reaction.
| Entry | Solvent | 1/sBuLi/(−)‐sparteine [equiv.] | Lithiation time [min] | Yield of 3 [a] [%] | e.r. of 3 |
|---|---|---|---|---|---|
| 1 | CPME | 1.0/1.3/1.3 | 120 | 65 | 97:3 |
| 2 | CPME | 1.5/1.6/1.6 | 120 | 70 | 97:3 |
| 3 | CPME | 1.9/2.0/2.0 | 120 | 72 | 97:3 |
| 4 | CPME | 1.5/1.6/1.6 | 60 | 78 | 97:3 |
| 5 | CPME | 1.5/1.6/1.6 | 30 | 95 | 97:3 |
| 6 | CPME | 1.5/1.6/1.6 | 15 | 45[b] | – |
| 7 | CPME | 1.0/1.3/1.3 | 30 | 81 | 97:3 |
| 8 | THF | 1.5/1.6/1.6 | 30 | 55 | 60:40 |
| 9 | toluene | 1.5/1.6/1.6 | 30 | 30 | 80:20 |
| 10 | Et2O | 1.5/1.6/1.6 | 30 | 21[b] | – |
| 11[c] | CPME | 1.5/1.6/1.6 | 30 | – | – |
| 12[d] | CPME | 1.5/1.6/1.6 | 30 | 18 | 94:7 |
| 13[e] | CPME | 1.5/1.6/1.6 | 30 | 91 | 97:3 |
[a] Isolated yields. [b] Byproducts were observed. [c] The corresponding ester was employed instead of 2. [d] The corresponding acid chloride was used instead of 2. [e] (−)‐Sparteine recovered from the reaction in entry 5 was employed.