Optimization of diastereodivergent reaction conditionsa.
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| Entry | Catalyst/acid | Solvent | Additive | Yieldb (%) | drc (3/4) | eec (%) |
| 1 | C1/OPA | — | — | 99 | 76 : 24 | 67/— |
| 2 | C1/OPA | — | 4 Å MS | 95 | >19 : 1 | 44/— |
| 3 | C1/TFA | — | 4 Å MS | 93 | >19 : 1 | 72/— |
| 4 | C1/TfOH | — | 4 Å MS | 95 | 85 : 15 | 80/— |
| 5 | C1-TfOH/TFA | — | 4 Å MS | 99 | >19 : 1 | 83/— |
| 6 | C1-TfOH/TFA | CH2Cl2 | 4 Å MS | 98 | >19 : 1 | 92/— |
| 7 | C1-TfOH/TFA | CH2Cl2 | H2O | 99 | 21 : 79 | —/93 |
| 8 | C1-TfOH/TFA | Et2O | H2O | 98 | 12 : 88 | —/93 |
| 9 | C1-TfOH/TFA | H2O | H2O | 98 | 11 : 89 | —/88 |
| 10d | C1-TfOH/TFA | Et2O | H2O | 98 | 10 : 90 | —/94 |
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a
Unless otherwise noted, all reactions were performed with catalyst/acid (1 : 1, 20 mol%), 1a (0.20 mmol), 2a (0.6 mL) at 35 °C for 20 h. If additive was added, the amount of 4 Å MS was 20 mg and H2O was 0.2 mL. If solvent was added, 2a (0.2 mL) in solvent (0.6 mL) for 12–16 h.
b
Isolated yields of two diastereomers.
c
Determined by SFC analysis on a chiral stationary phase.
d
The reaction was performed at 30 °C for 24 h. BA = benzoic acid; OHBA = o-hydroxybenzoic acid; OPA = o-phthalic acid; PFBA = pentafluorobenzoic acid; TfOH = trifluoromethanesulfonic acid; TFA = trifluoroacetic acid.