Revisiting the Synthesis of Functionally Substituted 1,4-Dihydrobenzo[][1,2,4]triazines.

A series of novel 1,4-dihydrobenzo[1,2,4][]triazines bearing an acetyl or ester moiety as a functional group at the C(3) atom of the 1,2,4-triazine ring were synthesized. The synthetic protocol is based on an oxidative cyclization of functionally substituted amidrazones in the presence of DBU and Pd/C. It was found that the developed approach is suitable for the preparation of 1,4-dihydrobenzo[][1,2,4]triazines, but the corresponding Blatter radicals were isolated only in few cases. In addition, a previously unknown dihydrobenzo[][1,2,4]triazolo[3,4-][1,2,4]triazine tricyclic open-shell derivative was prepared. Studies of thermal behavior of the synthesized 1,4-dihydrobenzo[1,2,4][]triazines revealed their high thermal stability (up to 240-250 °C), which enables their application potential as components of functional organic materials.