Reaction of Ethoxymethylenemalonate with Cyanothioacetamide in the Presence of Triethylamine: Formation of 1,5-Diamino-2,4-dicyano-5-thioxopenta-1,3-diene-1-thiolate and Unexpected Aminomethylation Result

Abstract The reaction of cyanothioacetamide with ethoxymethylenemalonate and triethylamine in ethanol upon heating is non-selective and leads to the formation of a mixture of triethylammonium 1,5-diamino-2,4-dicyano-5-thioxopenta-1,3-diene-1-thiolate and triethylammonium 6-oxo-3-cyano-5-ethoxycarbonyl-1 H -pyridin-2-thiolate with a predominance of the latter. When treating with primary amines and 37% formalin in boiling aqueous alcohol, the reaction product gives only 4-(1,3,5-thiadiazinan-2-ylidene)-2-(3,4-dihydro-2 H -1,3,5-thiadiazin-6-yl)pent-2-enedinitrile instead of the expected pyrido[2,1- b ][1,3,5]thiadiazine derivatives. Triethylammonium 6-oxo-3-cyano-5-ethoxycarbonyl-1 H -pyridin-2-thiolate does not react under these conditions.