Synthesis of nitrogen‐containing heterocycles. 7 Reaction of aliphatic diaminomethylenehydrazones with hindered ethoxymethylenecyanoacetate

Aliphatic diaminomethylenehydrazones 1 were reacted with ethyl 2‐cyano‐3‐ethoxy‐2‐pentenoate 2 to give a number of heterocycles in low to moderate yields, according to the substitution pattern and the size of substituent. When 1 carried a single methyl group on the terminal nitrogen, it gave preferentially 6‐oxo‐1,6‐dihydropyrimidines 4 incorporating N (4) into the ring. In contrast, the reaction between 1c or 1d and 2 led to 6‐imino‐ and 6‐oxo‐1, 6‐dihydropyrimidines 7 and 8 along with 3 . When the alkylidene moiety was bulky, 1e and 1f , the similar reaction gave 3 in high yields without any cyclized product. Upon exposure to acid, compound 3 yielded 6‐oxo‐1,6‐dihydropyrimidines 6 , [1,2,4]triazolo[1,5‐ c ]pyrimidine‐8‐carboxylate 5 and N ‐alkenyl‐1,2,4‐triazoles 9 in addition to 7 and 8 in proportions dictated by the nature of the substituents of 1 . The structural assignment and reaction mechanism are discussed.