Benzimidazole derivatives with primary N-alkyl substituents are easily synthesized by first deprotonating a benzimidazole nitrogen and reacting this anion with a primary haloalkane. However, this synthesis yields undesirable elimination products when secondary or tertiary haloalkanes are employed. Benzimidazole derivatives bearing secondary and tertiary alkane substituents have been synthesized in transition metal-catalyzed processes from diazoalkanes, but safety hazards presented by the diazo intermediates make the synthesis unsuitable for large-scale reactions. This study presents a novel synthesis for secondary and tertiary N-alkylated benzimidazoles that is safe and easily scalable. Fluoro-2-nitrobenzene is reacted with a secondary or tertiary amine in a microwave to yield an aminonitro compound that is then reduced to a diamine. The diamine is reacted with triethyl orthoformate to give the substituted benzimidazole.

Novel route to <i>N</i>-alkylated benzimidazoles

245th National Meeting (2013)

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Novel route to N-alkylated benzimidazoles