General procedure for the synthesis of 5,6-dichlorobenzimidazole from N-benzylbenzimidazole (CAS:6478-78-0, 208.1 mg, 1.0 mmol): to a 16 mL reaction flask equipped with a PTFE/silicone septum and a nitrogen bubbling device under nitrogen protection were added N-benzylbenzimidazole, a dry Pd/C catalyst (10 wt%. 20 mg) and THF (5 mL). Subsequently, triethylsilane (320 μL, 2.0 mmol) was slowly added to the reaction mixture at room temperature and stirred continuously for 14 h under nitrogen atmosphere. Upon completion of the reaction, the reaction mixture was filtered through a 0.45 μm PTFE syringe filter to remove the catalyst and the filtrate was concentrated under reduced pressure to remove the solvent. The residue was purified by column chromatography (eluent: 0 to 10% MeOH/dichloromethane gradient) to afford the target product 5,6-dichlorobenzimidazole as a colorless solid (117.6 mg, 0.996 mmol, 99% yield). It is worth noting that an induction period of 5 to 30 min usually exists at the beginning of the reaction, which is manifested by the beginning of gas release from the reaction mixture (i.e., the bubbling phenomenon). In addition, the use of a dry Pd/C catalyst is critical to the success of the reaction; wet Pd/C may result in a significant decrease in the reaction yield or no reaction at all.
