Pyridazines - 89. On the synthesis of novel 1,2-diazine containing tricyclic systems: Preparation of dipyridazinodiazepinones

A synthetic method for the so far unknown dipyridazino[4,3-b:3',4'-e][1,4]- diazepinone system (7a) was elaborated. Cyclisation of 6-chloro-N-(3,6-dich loropyridazin-4-yl)-3- (4-methoxybenzylamino)-N-propylpyridazine-4-carboxam ide (5) under basic conditions was found to yield in addition to the expect ed compound (7a) an isomeric dipyridazino[3,4-b:3',4'-e][ 1,4]diazepinone ( 7b) resulting from Smiles rearrangement. The 7a/7b ratio was found to be in fluenced by the nature of the base and the solvent.