Synthesis of Dimethyl 1-(Hetero)aryl-4-oxo-1,4-dihydropyridazine- 3,5-dicarboxylates from Dimethyl 3-Oxopentane-1,5-dioates

Dimethyl 3-oxopentane-1,5-dioate (dimethyl acetone-1,3-dicarboxylate) (1) was transformed first with (hetero)arenediazonium salts 3a - j into dimethyl 2-[(hetero)arylhydrazono]pentane-1,5-dioates 4a - j followed by reaction with N,N-dimethylformamide dimethylacetal (DMFDMA) to afford, without isolation of intermediates 5a - j, dimethyl 1-(hetero)aryl-4-oxo-1,4-dihydropyridazine-3,5- dicarboxylates 6a - j. An alternative method represents transformation of 1 with DMFDMA into dimethyl 2-[(dimethylamino)methylidene]-3-oxopentane-1,5-dioate (7) followed by treatment with (hetero)arenediazonium salts 3a - c, j to give pyridazine derivatives 6a - c,j.