Triazolines. Part 32. Synthesis of 1-alkyl-2-aminobenzimidazoles from 5-amino-1-(2-nitroaryl)-1,2,3-triazolines
摘要:
5-Amino-l-(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 8 as intermediates. Reduction of the nitro group to nitrene, addition to the C=N bond and rearrangement of the intermediate 2,2-disubstituted benzimidazoles accounts for the formation of the end products.
The synthesis of substituted benzimidazoles, 2-aminobenzimidazoles, 2-aminobenzothiazoles, and benzoxazoles is described via intramolecularcyclization of o-bromoaryl derivatives using copper(II) oxide nanoparticles in DMSO under air. The procedure is experimentally simple, general, efficient, and free from addition of external chelating ligands. It is a heterogeneous process and the copper(II) oxide