[1,2,4]Triazines. 4. Regiospecific ring closure reactions involving 6-amino-5-hydrazino[1,2,4]triazin-3(2H)-ones and orthoesters

6-Amino-5-hydrazino1,2,4]triazin-3(2H)-one, 3 , was treated with a variety of orthoesters and concentrated acid forming mixtures of ring-closed and open-chain derivatives. These mixtures were converted in warm aqueous acid to the Mriazolo5,1-d]1,2,4]triazin-3(2H)-ones, 11b, 14b , and 15b by a regiospecific ring closure at N-4 of the 1,2,4]triazine ring and subsequent Dimroth-like rearrangement of the initially formed s-triazolo4,3-d]1,2,4]triazin-3(2H)-ones ( 11a, 14a, 15a ).