Synthesis
GENERAL METHOD: 4-Iodo-2-nitroaniline (1 mmol) was mixed with indium powder (574 mg, 5.0 mmol) and acetic acid (0.572 mL, 10 mmol) in ethyl acetate (2 mL). Subsequently, a solution of ethyl acetate (3 mL for 2-nitroaniline; 8 mL for 1,2-dinitroaromatics) of trimethyl orthoacetate (2.0 mmol) was added. The reaction mixture was heated to reflux and stirred under nitrogen protection. Upon completion of the reaction, the reaction mixture was diluted with ethyl acetate (30 mL), filtered through diatomaceous earth and the filtrate was poured into 10% NaHCO3 solution (30 mL). The aqueous phase was extracted with ethyl acetate (30 mL x 3), the organic phases were combined and dried with anhydrous MgSO4, filtered and concentrated. The residue was purified by silica gel column chromatography using ethyl acetate/hexane (v/v=10/90) as eluent to obtain 2-methylbenzimidazole derivatives or methanol/dichloromethane (v/v=1/99) as eluent to obtain 5-iodo-2-methylbenzimidazole derivatives. The structures of the resulting benzimidazole derivatives were characterized by 1H NMR, 13C NMR, FTIR and GC-MS, with known compounds mainly confirmed by comparison with literature data and unknown compounds additionally provided with HRMS data.
References
[1] Tetrahedron, 2011, vol. 67, # 41, p. 8027 - 8033
