Control experiments on the catalytic role of C6 in the Diels–Alder reaction between 1,3-cyclohexadiene 4 and crotonaldehyde 5a.
| Entrya | TrX | Additiveb (equiv.) | 6a yieldc (%) | endo : exod |
|---|---|---|---|---|
| 1 | –Cl | Et4NBF4 (10) | — | — |
| 2 | –Cl | DMSO (30) | — | — |
| 3 | BF4− | — | 90 | >99 : 1 |
| 4e | BF4− | — | 43 | >99 : 1 |
| 5 | –Br | — | 68 | >99 : 1 |
| 6 | –I | — | — | — |
| 7 | –OH | — | — | — |
a
Reaction conditions: 4 (0.45 M), 5a (0.15 M), C6 and TrX (0.039 M) in 1.1 mL of water-saturated CDCl3, at 50 °C for 16 h.
b
Amount of additive with respect to C6.
c
Isolated yield.
d
Determined by 1H NMR analysis of the crude reaction mixture according to literature data.21
e
The reaction was performed in the absence of C6.