Table 1.
Effect of catalyst structure and counterion on cyclization
 | ||||
|---|---|---|---|---|
| entry | catalyst (R) | X− | yield (%)a | ee (%)b |
| 1 | 5 (H) | SbF6− | 41% | 89% |
| 2 | 6 (Ph) | SbF6− | 41% | 97% |
| 3 | 7 (1-naphthyl) | SbF6− | 43% | 99% |
| 4 | 7 (1-naphthyl) | ClO4− | 12% | 99% |
| 5 | 7 (1-naphthyl) | PF6− | 73% | 99% |
| 6 | 7 (1-naphthyl) | Tf2N− | 95%c | 99% |
a
Determined by 1H NMR using internal standard. Diastereoselectivity >20:1 in all cases.
b
Determined by chiral SFC analysis of the corresponding alcohol, absolute configuration determined by chemical correlation.
c
Isolated in 93% yield.