1,2,4‐Triazolo[4,3‐ c ]pyrimidines from 4‐acylhydrazinopyrimidines

The reaction of N 1 ‐acetylacetamidrazones 1 with N ‐[bis(methylthio)methylene]cyanamide (2) at room temperature in the presence of potassium carbonate in dimethyl sulfoxide affords good yields of ethyl 4‐acylhydrazino‐2‐amino‐6‐methylthio‐5‐pyrimidine carboxylate 3 . By briefly refluxing compounds 3 in dimethyl sulfoxide, 1,2,4‐triazolo[4,3‐ c ]pyrimidine derivatives 4 were obtained. When equimolecular amounts of N 1 ‐acylacetamidrazones and compounds 2 were refluxed in dimethyl sulfoxide/toluene, compounds 4 were obtained directly.