Table 1.
[4+2] Cycloaddition Reactions of 4.
| entry | dienophile (equiv) | conditions | product | % yield | ||
|---|---|---|---|---|---|---|
| 1 | 6a |
 (1.5) |
CH2Cl2, 25 °C, 1 min | 7a |
|
96% |
| 2 | 6b26 |
 (2) |
CH2Cl2, 25 °C, 15 min | 7b |
|
91% |
| 3 | 6c |
 (10) |
dioxane, 25 °C, 30 min | 7c |
|
85% |
| 4 | 6d |
 (10) |
dioxane, 25 °C, 30 min | 7d |
|
96% |
| 5 | 6e |
 (1.5) |
CH2Cl2, 25 °C, 16 h | 7d | 66% | |
| 6 | 6f |
 (10) |
CH2Cl2, 25 °C, 2 h | 7e |
|
91% |
| 7 | 6g |
 (5) |
CH2Cl2, 25 °C, 1 h | 7f |
|
94% |
| 8 | 6h |
 (5) |
dioxane, 100 °C, 1 h or dioxane, 25 °C, 24 h or dioxane, 25 °C, 48 h | 7f | 90%
54% 72% |
|
| 9 | 6i27 |
 (2) |
CH2Cl2, 25 °C, 2 h | 7g |
|
89% |
| 10 | 6j |
 (5) |
CH2Cl2, 25 °C, 2 h | 7h |
|
70% (5–11% regioisomer) |
| 11 | 6k |
 (5) |
dioxane, 100 °C, 9 h | 7i |
|
89% |