The reactions of 3-aryl-1,2,4-triazines with -aminovinyl ketones or ethyl -aminocrotonates in acetic anhydride at room temperature afforded cyclic products of the tandem nucleophilic addition, viz., 3a,4,7,7a-tetrahydro-1H-pyrrolo[3,2-e]-1,2,4-triazines, in good yields. Under oxidative conditions, the latter compounds underwent the pyrrole-ring opening under the action of potassium permanganate to form the corresponding triazinones and were transformed into thriazolyl-substituted pyridines under the action of selenious acid