Methyl and Imino

Reaction of activated methyl groups adjacent to arylazo groups with one-carbon synthons such as BBDM or DMFDMA gives fused pyridazines, by cyclization of the intermediate enamines. An example is the synthesis of 

An analogous reaction of the pyrimidinone (156) with triethyl orthoformate in trifluoroacetic acid gave the pyrimido[4,3-d]pyridazine (158) (78JOC2536). 

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