| Entry | Cobalt salt | Lewis acid | Yield/% | Selectivity | |
| 2 | 1 | 2/1 | |||
| 1 | CoCO3 | Sm(OTf)3 | 9.7 | 81.0 | 10.7/89.3 |
| 2 | Co(NO3)2∙6H2O | Sm(OTf)3 | 47.8 | 42.3 | 53.0/47.0 |
| 3 | CoCl2 | Sm(OTf)3 | 55.0 | 35.8 | 60.6/39.4 |
| 4 | Co(BF4)2∙6H2O | Sm(OTf)3 | 69.6 | 21.1 | 76.7/23.3 |
| 5 | Co(ClO4)2∙6H2O | Sm(OTf)3 | 80.6 | 5.6 | 93.5/6.5 |
| 6 | CoCO3 | Yb(OTf)3 | 14.7 | 75.6 | 16.3/83.7 |
| 7 | Co(NO3)2∙6H2O | Yb(OTf)3 | 52.1 | 37.6 | 58.7/41.3 |
| 8 | CoCl2 | Yb(OTf)3 | 73.1 | 16.8 | 81.3/18.7 |
| 9 | Co(BF4)2∙6H2O | Yb(OTf)3 | 68.3 | 24.1 | 73.9/26.1 |
| 10 | Co(ClO4)2∙6H2O | Yb(OTf)3 | 74.1 | 19.0 | 79.5/20.5 |