Unexpected hydrazinolysis behaviour of 1-chloro-4-methyl-5H-pyridazino[4,5-b]indole and a convenient synthesis of new [1,2,4]-triazolo[4',3':1,6]pyridazino[4,5-b]indoles.

Reaction of the title compound with hydrazine in the presence of air gives the 1-unsubstituted parent system via oxidative dehydrazination of the 1-hydrazino intermediate. The latter can be obtained in high yield by carrying out the hydrazinolysis step under inert gas, and it is smoothly converted into [1,2,4]-triazolo[4',3':1,6]pyridazino[4,5- b]indoles.