Abstract
AbstractThe reaction between dimethyl acetylene dicarboxylate and 2‐amino‐1‐methylimidazole affords dimethyl 2‐amino‐1‐methyl‐1,3‐diazepine‐5,6‐dicarboxylate in low yield. This 1:1 – adduct was formed by addition of the acetylenic compound to the enamine double bond of the imidazole ring followed by ring enlargement. On the other hand, 2:1 – adducts to the imine bond are isolated in moderate yield when dimethyl acetylene dicarboxylate is treated with either 1‐methyl‐2‐methylmercapto‐imidazole or 1‐methyl‐2‐methylmercapto‐imidazoline. These adducts behave differently on heating with ethylamine: the adduct of the imidazole series cyclizes to the pyridone 15 with concomittant loss of one carboxamide group whereas that of the imidazoline series forms a pyrido[1,2‐a]pyrazine derivative 20, both in high yield. The possible reaction mechanisms are discussed. 13C–NMR.‐spectroscopy and X‐ray analysis were used in the determination of several structures.
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