A short synthesis of phenanthro[2,3-d]imidazoles from dehydroabietic acid. Application of the methodology as a convenient route to benzimidazoles

Methyl cis-deisopropyldehydroabietate was selectively nitrated at the 12-position by reaction with ‘claycop’, a montmorillonite clay impregnated with copper(II) nitrate. The 12-nitro compound was reduced to the corresponding amine and this was subjected to a combined acylation and ortho nitration. The compounds so produced were further converted into octahydro-1H-phenanthro[2,3-d]imidazoles by reductive cyclization. The same acylation-ortho nitration methodology was shown to provide a short synthesis of 2-substituted benzimidazoles from aniline.