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

Abstract

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, pyrido[3,4‐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).

Synthetic Pathways to Pyrido[3,4-c]pyridazines and Their Polycyclic Derivatives

“…Unfortunately, only a low yield of 10 (14-17%) was obtained after chromatography. In a later effort [11], the same strategy was applied to obtain the corresponding pyrido [3,4-c]pyridazine-4-one 12b from 4-acetyl-3-aminopyridine 11. This Borsche reaction probably involves the electron rich enol form of the acetyl substituent, to afford (38% yield) a tautomeric equilibrium mixture of 12a,b.…”