Science of Synthesis

Irudayanathan, F. M.; Lee, S., Science of Synthesis Knowledge Updates, (2019) 2, 3.

The reaction of benzene-1,2-diamine with benzaldehyde in the presence of palladium (e.g., Pd/C) and montmorillonite K-10 results in a mixture of 2-phenyl-1H-benzimidazole (‌4‌) and 1-benzyl-2-phenyl-1H-benzimidazole (‌5‌) (‌Scheme 2‌).[‌2‌] Optimization of the reaction conditions revealed that the selectivity between ‌4‌ and ‌5‌ is remarkably temperature-dependent. If the reaction is performed above 60 °C, a significant amount of 1-benzyl-2-phenyl-1H-benzimidazole (‌5‌) is formed, but the amount of this byproduct is greatly reduced if the reaction is conducted at lower temperatures. In fact, when the reaction is performed at temperatures from 4 °C to room temperature, formation of only traces of ‌5‌ is observed, even in the presence of two equivalents of benzaldehyde.

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