7‐Azacinnolin‐4(1H)‐one preparation and NMR studies of tautomery

As part of our current investigations of nitropyridines, we hereby report the preparation of a new annulated heterocycle by C‐azo coupling. Thus, the azacinnoline, pyrido3,4‐c]pyridazin‐4(1H)‐one (38%), was prepared from 4‐acetyl‐3‐aminopyridine via diazotization. ¹H, ¹³C, and ¹⁵N NMR spectroscopic investigations revealed that the azacinnoline exclusively exists in the NH‐keto tautomeric form in DMSO‐d₆, CD₃OD, and D₂O. J. Heterocyclic Chem., (2011).