Table 1.
Catalyst screening and optimization.
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| entrya | HX (mol %) | solvent | temp (°C) | time (h) | conv. (%) | yield (%)b |
| 1 | HCl (500) | EtOAc/toluene | 100 | 16 | 0 | – |
| 2 | HOAc (100) | EtOAc | 85 | 12 | 0 | – |
| 3 | HOAc (500) | toluene | 120 | 16 | 0 | – |
| 4 | (+)-CSAc (100) | toluene | 120 | 12 | 100 | 60 |
| 5 | HO2CCF3 (500) | toluene | 85 | 7 | 79 | 39 |
| 6 | HO2CCF3 (100) | toluene | 85 | 5 | 100 | 50 |
| 7 | HO2CCF3 (100) | EtOAc/toluene | 110 | 4 | 92 | 41 |
| 8 | HO2CCF3 (50) | toluene | 150 | 3 | 100 | 87 |
| 9 | HO2CCF3 (90) | toluene | MWd | 1.5 | 94 | 65 |
aAll reactions run in a sealed tube. Concn = 0.03–0.04 M; 5.0 equiv Na2SO4. bIsolated yields. c(+)-Camphorusulfonic acid. d450-W Microwave.