6‐(substituted phenyl)‐5‐methyl‐4,5‐dihydro‐pyridazin‐3(2H)‐ones of medicinal interest. The synthesis of SK&F 94836 and SK&F 95654

Two synthetic routes to the dihydropyridazinone‐cyanoguanidine 4 (SK&F 94836) are described, both proceeding via the anilino compound 6. An efficient synthesis of the dihydropyridazinone‐pyridone 5 (SK&F 95654) is reported. This synthesis proceeds via the fluoro‐keto‐acid 24, with subsequent displacement of the fluoro substituent by 4‐pyridone. The surprising effectiveness of water as a solvent in this reaction has been highlighted.