The possibility of spontaneous reduction of benzofuroxans to benzofurazans in course of time due to reactions with diamines was shown for the first time. A possible mechanism of the reaction of 4,6-dichloro-5-nitrobenzofuroxan with diamines and related amines was analyzed by the quantum-chemical method. The results of research fully confirm the obtained experimental data and explain the impossibility of the subsequent reduction of amino-containing benzofuroxans due to a high activation barrier.