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Acid screen for tandem ring closing reaction.
| Entry | Acid (pKa) | Equiv. | Ratio 25:23 |
|---|---|---|---|
| 1 | - | - | no conv. |
| 2 | TFA (−0 25) | 1 | 1:4 5 |
| 3 | PTSA (−2.8) | 1 | 1:2.2 |
| 4 | AcOH (4 76) | 1 | >1:20 |
| 5 | CSA (12) | 1 | 1:1.3 |
| 6 | CSA (12) | 2 | >20:1 |
*To a solution of tetraene 23 in toluene was added an acid.. After stirring for 10 minutes Grela catalyst (10%) was added and stirring was continued at rt for 7 h..
