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Optimization of selectivity of benzimidazole 5 over 6.
| Entry | Conditions | Ratio of 5 : 6 [a] |
|---|---|---|
| 1 | 120 °C, 1 h | 4 : 1 |
| 2 | 60 °C, 16 h | 4 : 1 |
| 3 | 45 °C, 16 h | 20 : 1 |
| 4 | 22 °C, 16 h | >100 : 1 |
| 5 | 4 °C - rt, 16 h | >100 : 1 |
| 6 | 4 °C - rt, 16 h, 2 equiv. of PhCHO | 100 : 1 |
Determined by 1H NMR spectroscopy of crude reaction mixture.
