A novel tetracyclic ring system. 10H-tetrazolo[5′,1′:3,4][1,2,4]triazino[5,6-b]indole

The reaction of 3-hydrazino-1,2,4-triazino5,6-b]indole with nitrous acid affords a novel tetracyclic ring system: 10H-tetrazolo5′,1′:3,4]1,2,4]triazino5,6-b]indole. The mode of cyclization has been discussed.