A Convenient Synthesis of 1,2-Diaminobenzimidazoles and Their Oxidation to 3-Amino-1,2,4-Benzotriazines

Abstract

Recent work by Ho and Day¹ described the preparation of 1,2-diaminobenzimidazoles via the cyclization of N-acethydrazido-anilines with cyanogen bromide. In an attempt to shorten this multistep synthesis, several amination procedures were investigated.² Of these, the reaction of hydroxylamine-O-sulfonic acid with 2-aminobenzimidazoles was found to be the most convenient route to 1,2-diaminobenzimidazoles. Subsequent oxidation of these compounds with lead tetraacetate provided the corresponding 3-amino-1,2,4-benzotriazines in good to excellent yields.