Table 7.
| |||||
---|---|---|---|---|---|
entry | catalyst | yield (2b) b | yield (2b′) b | ratio (2b:2b′) c | combined yield b (2b+2b′) |
1 | Ni(cod)2/Ph3P | 78% | 6% | 93:7 | 84% |
2 | Ni(Ph3P)4 | 41% | 3% | 93:7 | 44% |
3 | Ni(acac)2/Ph3P/DIBAL-H | 72% | 5% | 93:7 | 77% |
4 | Ni(Ph3P)2Cl2/n-BuLi | 32% | 2% | 94:6 | 34% |
5 | Ni(Ph3P)2Br2/n-BuLi | <5% | <5% | n.d. | <5% |
Standard procedure: The nickel precatalyst system (20 mol%) was dissolved in 2.5 mL toluene. The alkene (1 mL), triethylamine (600 mol%), the aldehyde (100 mol%, 0.5 mmol), and Et3SiOTf (175 mol%) were added. The reaction mixture was stirred 48 h at 23 °C.
Yields were determined by 1H NMR using DMF as a standard.
Ratios were determined by 1H NMR of the crude reaction mixture.