Purines, Pyrimidines, and Condensed Systems Based on them. 18. Reaction of 6,8-Dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)dione N(2)-oxide with Alkylamines

Heating 6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-dione N₍₂₎-oxide (2) with piperidine or morpholine gave a moderate yield of 3-piperidino- and 3-morpholino-6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones (3a,b). Reaction of N-oxide (2) with ammonia and alkylamines in the presence of an oxidant led to formation of the 3-amino derivatives of 2 and the corresponding desoxy products 3. The latter were also obtained by an independent method by heating 3-chloro-6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-dione with alkylamines in butanol.