Regioselectivity of N-substitution in bis-alkylation of 1,2,4-triazolo[1,5-a]benzimidazole-2-thione

Cyclization of the corresponding N-substituted 1,2-diaminobenzimidazoles with carbon disulfide in refluxing DMF leads to 3-methyl- and 3-benzyl-1,2,4-triazolo1,5-a]benzimidazole-2-thiones. Based on the results of their S-alkylation, quantum chemical calculations by the density functional theory method, and 1D and 2D NMR spectroscopic studies, it was concluded that the bis-alkylation of N-unsubstituted 1,2,4-triazolo1,5-a]benzimidazole-2-thione in the presence of a base proceeds with the formation of N(4)-derivatives of 2-alkylthio-1,2,4-triazolo1,5-a]benzimidazole, rather than N(3)-derivatives as was believed earlier.