Table 3.
Optimization of the reaction conditions of 2-naphtol (15) with N-tosylimine 13 catalyzed by thiourea 1.
| Entry | 2-Naphthol (eq.) | N-tosylimine (eq.) | mol% Cat. | Temp. [°C] | Yield [%] 1 | ee [%] 2 (Conf.) 3 |
|---|---|---|---|---|---|---|
| 1 | 5 | 1 | 10 | 0 | 90 | 34 (S) |
| 2 | 3 | 1 | 10 | 0 | 98 | 54 (S) |
| 3 | 3 | 1 | 10 | 20 | 95 | 24 (S) |
| 4 | 1.5 | 1 | 10 | 0 | 85 | 24 (S) |
| 5 | 3 | 1 | 5 | 0 | 90 | 52 (S) |
| 6 | 3 | 1 | 30 | 0 | 87 | 42 (S) |
Reagents and conditions: 2-naphthol (0.15 mmol, 3 eq.), N-tosylimine (0.05 mmol, 1 eq.), toluene (1 mL), molecular sieves 4 Å, 20 h. 1 Isolated product. 2 Determined by HPLC analysis, Chiralpak OD-H, hexane:iPrOH 94:6, 1 mL/min, 235 nm. 3 The configuration was established by comparison with the optical rotation from the literature [11,13].