Table 4. Optimization of Cyclization to indole 3a.
entry | Lewis acid | X | solvent | temp (°C) | yield (%) |
---|---|---|---|---|---|
1 | none | CH2Cl2 | 45 | 0 | |
2 | AlCl3 | 0.2 | CH2Cl2 | 45 | 0 |
3 | Sc(OTf)3 | 0.2 | CH2Cl2 | 45 | 0 |
4 | TiCl4 | 0.2 | CH2Cl2 | 45 | 0 |
5 | BF3·OEt2 | 0.2 | CH2Cl2 | 45 | 19 |
6 | BF3·OEt2 | 1.1 | THF | 70 | 0 |
7 | BF3·OEt2 | 1.1 | PhCH3 | 85 | 61 |
8 | BF3·OEt2 | 2.5 | DCE | 90 | 91 |