Synthesis
To a 16 mL reaction flask equipped with a PTFE/silicone septum and a nitrogen bubbler was added N-benzylbenzimidazole (208.1 mg, 1.0 mmol), dried Pd/C catalyst (10 wt%, 20 mg) and THF (5 mL). Triethylsilane (320 μL, 2.0 mmol) was added dropwise to the mixture under nitrogen protection, followed by continuous stirring at room temperature for 14 hours. After completion of the reaction, the reaction mixture was filtered through a 0.45 μm PTFE syringe filter and the filtrate was concentrated under reduced pressure. The residue was purified by column chromatography (eluent: 0 to 10% methanol/dichloromethane gradient) to afford 5-methoxybenzimidazole as a colorless solid (117.6 mg, 0.996 mmol, 99% yield). It is worth noting that the reaction typically suffers from an induction period of 5 to 30 min, which can be observed by the release of gas from the reaction mixture (i.e., the bubbling phenomenon). The use of a dry Pd/C catalyst is critical to the success of the reaction, and wet Pd/C may result in a significant decrease in yield or inability of the reaction to proceed.
References
[1] Tetrahedron Letters, 2015, vol. 56, # 21, p. 2688 - 2690
