The one-step synthesis of new bis[1,2,4-triazolo][4,3-a:3′,4′-d][1,5] benzodiazepines by way of completely regio- and diastereoselective 1,3-dipolar cycloaddition of nitrilimines to 2,4-dimethyl-3H-1,5-benzodiazepines is reported and a tentative rationalization for the observed diastereoselectivity, which underline the key effect of the C4-dipolarophile substituent, is proposed.