The first synthesis of novel fused pyridazines has been realized starting from 1,3-diketones involving a Diaza–Wittig reaction as a key step. A convenient strategy was elaborated to access versatile pyridazine derivatives allowing the variation of substituents at position 6 of the heterocyclic ring. In a first part, pyridazines bearing an ester group were synthesized as a model to evaluate the methodology. In a second part, an improved procedure has been used for the synthesis of pyridazines bearing a ketone group and different methods of cyclization were carried out, leading to several hitherto unknown biheterocyclic compounds. This reaction scheme represents an attractive methodology for the synthesis of novel fused pyridazine derivatives.