Triazolines. Part 32. Synthesis of 1-alkyl-2-aminobenzimidazoles from 5-amino-1-(2-nitroaryl)-1,2,3-triazolines

Abstract

5-Amino-1-(2-nitroaryl)-1,2,3-triazolines 5 are converted into 1-alkyl-2-aminobenzimidazoles 7 in refluxing triethyl phosphite. The reaction occurs via thermal rearrangement of 5 followed by nitrogen elimination which produces N²-(2-nitroaryl)amidines 6 as intermediates. Reduction of the nitro group to nitrene, addition to the CN bond and rearrangement of the intermediate 2,2-disubstituted benzimidazoles accounts for the formation of the end products.