A novel crystalline tetrazolo‐azido isomer pair: Pyrido[ 2,3‐e] tetrazolo[5,1‐c]‐as‐triazine and 3‐azidopyrido[2,3‐e]‐as‐triazine; the synthesis of tetrazolo[5,1‐c] benzo‐as‐triazine and pyrido[2,3‐e]‐s‐triazolo[3,4‐c] ‐as‐triazine

The deoxygenated derivative of 3‐azidobenzo‐ as ‐triazine 1‐oxide (II) exists in solution predominantly as 3‐azidobenzo‐ as ‐triazine form (IVa) but in the crystalline state as tetrazolo[5,]‐ c ]‐benzo‐ as ‐triazine (IVb), a new fused heteroaromatie ring system. With the pyrido[2,3‐ e ]‐ as ‐triazine derivatives, however, both 3‐azidopyrido[2,3‐ e ]‐ as ‐triazine (X) and pyrido[2,3‐ e ] tetra‐zolo[5,1‐ e ]‐ as ‐triazine (XI) can be isolated in crystalline form, and these are interconvertible. Another new ring system, the pyrido[2,3‐ e ] triazolo [3,4‐ c ]‐ as ‐triazine (XVII) and its derivatives has also been synthesized.