First synthesis of 5,8-dichloro-3-(2-pyridyl)benzo[e][1,2,4]triazines by reaction of 3,3,6,6-tetrachloro-1,2-cyclohexanedione with 2-pyridylamidrazones. Characterization of unexpected bishemiaminal intermediates

A new approach to selected 1,2,4-benzotriazines has been developed. 3,3,6,6-Tetrachloro-1,2-cyclohexanedione reacted with 2-pyridylamidrazones to give unexpected isolable bishemiaminal intermediates instead of the corresponding ketodiazenes. Subsequent dehydration gave 5,5,8,8-tetrachloro-3-(2-pyridyl)-5,6,7,8-tetrahydrobenzo[e][1,2,4]triazines, which were converted into previously unknown 5,8-dichloro-3-(2-pyridyl)benzo[e][1,2,4]triazines by dehydrochlorination under basic conditions. Severe limitations of reactions between o-benzoquinones with amidrazones have been circumvented in this manner. This preparative process has also been adapted to a one-pot protocol.