Table 1.
Exploratory studies.
| Entry | Catalyst (R) | Solvent | Additive | Yield [%][a] | ee [%][b] |
|---|---|---|---|---|---|
| 1 | 4 a (TMS) | toluene | – | 38 | 90 |
| 2 | 4 a (TMS) | o‐Cl2C6H4 | – | 52 | 83 |
| 3 | 4 a (TMS) | o‐Cl2C6H4 | DPP | 60 | 86 |
| 4 | 4 b (TBS) | o‐Cl2C6H4 | DPP | 61 | 90 |
| 5[c] | 4 b (TBS) | o‐Cl2C6H4 | DPP | 0 | – |
| 6 | none | o‐Cl2C6H4 | DPP | 18 | – |
[a] Yield of isolated 5 a. [b] Determined by HPLC analysis on a chiral stationary phase. [c] Reaction in the dark. BLB=black light bulb (λ max=365 nm), DPP=diphenylphosphoric acid, o‐Cl2C6H4=1,2‐dichlorobenzene, TMS=trimethylsilyl, TBS=tert‐butyldimethylsilyl.