Table 3. Optimization of Retro-Diels–Alder.
| solvent | time (min) | conc (M) | relative conversiona | yieldb |
|---|---|---|---|---|
| 1,2,4-trichlorobenzene | 90 | 0.05 | 1 | N/D |
| 30 | 0.05 | 1.21 | N/D | |
| 30 | 0.025 | 1.27 | N/D | |
| Dowtherm A | 30 | 0.025 | 1.41 | 74% |
| 30 | 0.1 | N/D | 69% |
a
18 was diluted in the indicated solvent in a vial under a slight positive pressure of nitrogen equipped with a vent needle. The solutions were heated to 160 °C for the indicated reaction time. An internal standard was added, and the amount of product formed, relative to the internal standard, was determined by LC analysis. Relative conversion is defined as the ratio of product to internal standard, divided by that ratio for the first table entry.
b
Reactions were performed on a 1 mmol scale.