Table 1 Optimization of the reaction conditionsa.
| |||||||
|---|---|---|---|---|---|---|---|
Entry | Solvent | Catalyst (%) | Time (h) | Yield (%)b | 3a:4a | ||
2a | 3a | 4a | |||||
1 | toluene | 1a (5) | 4.5 | 55 | 7 | 0 | − |
2 | THF | 1a (5) | 4.5 | 75 | 4 | 0 | − |
3 | CH3NO2 | 1a (5) | 4.5 | 25 | 2 | 0 | − |
4 | cyclohexane | 1a (5) | 4.5 | 53 | 12 | 0 | − |
5 | CH2Cl2 | 1a (5) | 4.5 | 55 | 20 | 0 | − |
6 | EA | 1a (5) | 4.5 | 36 | 22 | 0 | − |
7 | acetone | 1a (5) | 4.5 | 34 | 41 | 0 | − |
8 | CH3CN | 1a (5) | 4.5 | 0 | 83 | 4 | 95:1 |
9 | CH3OH | 1a (5) | 4.5 | 0 | 95 | 3 | 97:1 |
10 | CH3OH | 1b (5) | 5 | 0 | 93 | 1 | 99:1 |
11 | CH3OH | 1c (5) | 5 | 0 | 99 | <1 | >99:1 |
12 | CH3OH | 1d (5) | 5.5 | 0 | 94 | 1 | 99:1 |
13 | CH3OH | 1e (5) | 4.5 | 22 | 3 | 0 | − |
14 | CH3OH | 1c (1) | 5 | 0 | 99 | 1 | 99:1 |
15 | CH3OH | 1c (0.1) | 5 | 0 | 99 (93)c | <1 | >99:1 |
16 | CH3OH | 1c (0.01) | 5 | 16 | 78 | 0 | − |
17 | CH3OH | − | 5 | 77 | 1 | 0 | − |
18d | CH3OH | 1c (0.1) | 5 | 78 | 0 | 0 | − |
19d,e | CH3OH | 1c (0.1) | 5 | 76 | 0 | 0 | − |
